Universitatea din Craiova [309791]

HABILITATION THESIS

Title: CONSTANT VOLUME CRYOPRESERVATION

Domain: Mechanical Engineering

Author: Prof. dr. ing. Alenxadru ȘERBAN

University Transilvania of Brașov

BRASOV, 2016

Contents

Contents 1

Acknowledgement 2

List of notations 3

List of abbreviations 4

1. Rezumat (4000-6000 caractere) 5

2. Summary (4000-6000 characters) 7

3. Scientific and professional achievements and the evolution and development plans for career development 9

4. Scientific and professional achievements (min. 150000 characters) 9

4.1. [anonimizat] 9

4.1.1. [anonimizat] 10

4.1.2. [anonimizat] 12

4.1.3. [anonimizat], modified from gas heated generator in warm water heated generator 19

4.1.4. Adsorption cooling 19

4.1.5. Evaporative cooling 22

4.1.6. Use of natural refrigerants 24

4.2. [anonimizat] 28

4.2.1. New technologies in the field of air separation 28

4.2.2. [anonimizat] 36

4.2.3. Properties and applications of helium and neon 43

4.3. The study of heat and mass transfer in buildings and building services 48

4.3.1. Testing laboratory using renewable sources for radiant heating & cooling 48

4.4. [anonimizat] 51

4.4.1. Wind power in Romania 51

4.5. Appliacations of refrigeration and cryogenics in Bioengineering 59

4.5.1. The history and origins of Cryogenics 59

4.5.2. The history and origins of biological material preservation 64

4.5.3. Preservation in the constant pressure system 67

4.5.4. Preservation in a hyperbaric system 68

4.5.5. Isochoric freezing method. Process description and device proposal 69

4.5.6. Sizing the hyperbaric container and strength verification 81

4.5.7. Preliminary results with the ischoric preservation system [115] 101

4.6. Conclusion 108

5. The evolution and development plans for career development (max. 25000 characters) 113

5.1. Previous professional activity results 113

5.2. Professional and academic activity: 113

5.3. Research activity 120

5.3.1. Works in the field of Cryogenics 120

5.3.2. Works in the filed of Refrigeration 120

5.3.3. Works in Heat and Mass transfer in Buildings and Building Services 120

5.4. [anonimizat] 121

5.4.1. Diversification of curricula and methods of transmitting knowledge 121

5.4.2. Refrigeration 121

5.4.3. Technical Cryogenics 121

5.4.4. Teaching career and educational development 122

5.4.5. Research development 123

6. References 125

[anonimizat]. [anonimizat], [anonimizat].

[anonimizat] 2016

List of notations

Di Inner diameter;

Dext Outer diameter;

Vutil Useful volume;

Hutil Useful height;

σt is tangential tension;

σr is the radial tension;

σech is the equivalent stress;

Ri, Re is the inner radius, respectively thick wall outer cylinder;

pi, pe is the pressure on the inner surfaces, outer respectively;

n is the total number of cylinders

0 is the index for the inner surface of the container

kn is the ratio between Rn and Rn-1

ui, Rj is the deformation of the cylinder i calculated for surface of the radius j

v is the Poisson coefficient

E is elasticity module at a temperature of calculation

List of abbreviations

ISI International Scientific Indexing;

CEO Chief Executive Officer;

VRV Variable Refigerant Volume;

UTCB Universitatea Tehnică de Cosntrucții București (Technical University of Civil Engineering Bucharest);

UNITBV Universitatea Transilvania din Brașov (Transilvania University of Brasov);

HVAC Heating, Ventialtion and Air Conditioning;

AHU Air Handeling Unit;

UNEP United Nations Environment Programme;

IIR International Institute of Refrigeration;

CFC Chlorofluorocarbon;

HCFC Hydrochlorofluorocarbon;

GWP Global Warming Potential;

ODP Ozone Depletion Potential;

HP High Pressure;

LP Low Pressure;

LOX Liquid Oxigen;

GOX Gaseous Oxigen;

LIN Liquid Nitrogen;

ASU Air Separation Unit;

FEP Front-end Purification;

TSA Thermal Swing Adsorption;

PLC Programmable logic controller;

EU European Union;

RES Renewable Energy Sources;

DMSO Dimethyl Sulfoxide;

NGM Nematode Growth Medium;

MRI Magnetic Resonance Imaging;

MAGLEV Magnetic Levitation;

ANRE Romanian Regulatory Authority for Energy;

Rezumat (4000-6000 caractere)

Teza de abilitare intitulată „Crioconservare la volum constant” prezintă principalele preocupări științifice, profesionale și de cercetare pe care le-am desfășurat de la finalizarea tezei de doctorat, în domeniul Inginerie Mecanică, din anul 2004 (diploma seria D, nr. Minister 0003843, în baza Ordinului Ministrului Educației și Cercetării nr. 5237 din 05.11.2004), până în prezent, evidențiind, totodată și activitatea desfășurată de la obținerea titului de profesor universitar (2014) și până în prezent, dar mai ales preocuparile mele actuale.

În această perioadă am desfășurat activitățile precizate în cadrul Universității Tehnice de Construcții București, la Facultatea de Inginerie a Instalațiilor (2007 – 2009), în cadrul Universității Transilvania din Brasov, la Facultatea de Construcții, Departamentul de Instalații pentru Construcții (2009-prezent) și în cadrul Universității Politehnica București (2014-prezent), în calitate de cardu didactic asociat.

Prezenta lucrare este structurată pe 5 capitole și o bibliografie în care sunt prezentate realizările științifice.

Primul capitol este dedicat rezumatului în limba română, cel de-al doilea capitol fiind rezumatul tezei de abilitare în limba engleză. În capitolul al treilea sunt prezentate succint realizările științifice și profesionale și planurile de dezvoltare a carierei. Următoarele două capitole reprezintă o continuare a capitolului precedent, în capitolul patru fiind detaliate realizările științifice și profesionale, iar în capitolul cinci fiind prezentate planurile de evoluție și dezvoltare a carierei. Ultima parte a acestei lucrări este dedicată referințelor bibliografice.

Activitatea mea didactică și de cercetare s-a centrat de-a lungul timpului, în sfera domeniului în care am susținut și teza de doctorat, cu precădere în domeniul Instalațiilor Frigorifice și al Criogeniei. Mai recent, după obținerea titlului de Profesor, activitatea didactică și de cercetare a fost extinsă. Activitatea didactică a fost îmbogățită cu două cursuri predate la ciclul de Master, Instalații utilizate în construcții bazate pe enegie solară și Optimizarea performanței energetice a anvelopei clădirilor. Activitatea de cercetare a fost extinsă și către domeniul energiilor regenerabile, în care am publicat deja un articol ISI, în jurnalul Renewable and Sustainable Energy Reviews, cu factor de impact 6,798, în care este prezentată situația energiei eoliene din România iar un al doilea este în recenzie la același jurnal și este despre energia hidroelectrică în țara noastră, de la începuturile ei până în prezent. Activitatea de cercetare a fost direcționată și în sfera aplicării instalațiilor frigorifice în climatizarea de confort pentru clădiri, al instalațiilor de răcire folosind sisteme de transmitere a energiei prin radiație, al analizei performanței energetice a elementelor de construcție și al promovării și aplicării unor metode noi de predare. Desigur, și la această activitate am pregătit o serie de articole ISI, care sunt în recenzie iar altele au fost deja publicate în cadrul unor conferințe indexate ISI. Cea mai nouă activitate de cercetare, care mă preocupă este legată de aplicarea cunoștințelor de frig și criogenie în domeniul Bioingineriei. În acest sens sunt implicat în cercetarea și dezvoltarea unui sistem de conservarea a materiei biologice la temperaturi sub zero grade, la volum constant și în cercetarea și dezvoltarea unei imprimante 3D pentru printarea de țesuturi, în mediu de azot lichid. O parte din cercetarile mele referitoare la sistemul de crioconservare la volum constant au fost deja publicate în cadrul unui articol ISI, la jurnalul internațional Biochemical and Biophysical Research Communications, cu factorul de impact 2,371 iar o parte sunt prezentate și în cadrul acestei teze de abilitare.

De-a lungul timpului am publicat în calitate de prim autor, coautor și autor corespendent, mai mult de 60 de articole și 6 cărți, dintre care 4 ca prim autor și 2 în calitate de coautor.

Relevanța activității științifice și recunoașterea activității naționale și internaționale în domeniul Ingineriei Mecanice este subliniată de publicațiile mele, multe dintre ele în colaborare cu cercetători recunoscuți din țară, din Europa sau Statele Unite. Valoarea reală a studiilor efectuate și a proiectelor de cercetare iese în evidență prin faptul că toate problemele au fost investigate atât printr-o abordare teoretică cu simulări numerice, precum și cu parte experimentală, care să confirme rezultatele teoretice.

În anul 1994 am înființat, împreună cu un grup de colegi specialiști în domeniu, firma privată CRIOMEC SA Galați, la care m-am transferat în anul 1999, în funcția de Director General și Președinte al Consiliului de Administrație (calitate ce o dețin și în prezent). Această companie are ca domeniu principal de activitate: proiectarea, execuția, montajul și reparația instalațiilor industriale, criogenice, petrochimice și metalurgice.

Sunt membru în academii, organizații, asociații profesionale de prestigiu, naționale și internaționale, ce au apartenență la organizații din domeniul educației și cercetării.

Creșterea standardelor de excelența academică, vor trebui permanent urmărite și promovate în marea familie din Universitate formată din: studenți, cadre didactice, cercetători și personal auxiliar, implicându-mă activ în toate inițiativele menite să crească importanța și vizibilitatea colectivului Universității.

Brașov, Prof. dr. ing. Alexandru ȘERBAN

iulie 2016

Summary (4000-6000 characters)

Habilitation Thesis on "Cryopreservation at constant volume" presents the main concerns of scientific, professional and research that I conducted after completion of the Doctoral Thesis in the field of Mechanical Engineering, 2004 (diploma Series D, no. Minister 0003843, based on Minister of Education and Research Order no. 5237 of 05.11.2004), up to now, highlighting in the same time, the work done after obtaining the title of Professor (2014) and so far, especially my current concerns.

During this period, I conducted activities in the Technical University of Civil Engineering, Faculty of Building Services (2007-2009), at Transilvania University of Brasov, Faculty of Civil Engineering, Department of Building Services (2009-present) and the Polytechnic University of Bucharest (2014-present), as associate professor.

This paper is structured into five chapters and a reference list, where I presented my scientific achievements.

The first chapter is devoted to a summary in Romanian language; the second chapter is the summary of the habilitation thesis in English. In the third chapter I am summarizing the scientific achievements and professional and career development plans. The next two chapters are a continuation of the previous chapter, in chapter four being detailed the scientific and professional achievements, and in chapter five the development plans and career development. The last part of this paper is devoted to references.

My teaching and research were centered over time, within the field in which I supported my doctoral thesis, especially in the field of Refrigeration and Cryogenics. More recently, after obtaining the title of Professor, teaching and research have been extended. The teaching activity has been enriched with two courses taught Master cycle, Plants used in buildings based on solar energy and Energetic optimization performance of the building envelope. The research was extended to renewable energies, where I have already published an ISI article in the journal of Renewable and Sustainable Energy Reviews, impact factor 6.798, outlining the state of wind energy in Romania and a second is in review at the same journal and is about hydropower in our country, from its beginnings to its present development. The research was directed in the sphere of application of refrigeration systems in air conditioning for comfort in buildings, cooling systems by radiation, analyzing energy performance of building components and the promotion and application of new teaching methods. Of course, in this work we have prepared a series of articles in ISI who are in review, and others have already been published in ISI conferences. The new research, which concerns me is related to refrigeration and cryogenic knowledge application to the field of Bioengineering. In this sense, I am involved in researching and developing a system of conservation of biological material at subzero temperatures, constant volume and in the research and development of 3D printer for printing tissues in liquid nitrogen environment. Part of my research in the system of cryopreservation at constant volume has already been published as an article ISI, in the International Journal of Biochemical and Biophysical Research Communications, with the impact factor of 2,371 and some are presented in this thesis.

Over time I have published as first author, co-author and correspondent author, more than 60 articles and six books, 4 of which as primary author and two as co-author.

The relevance of the scientific work and the work of national and international recognition within the field of Mechanical Engineering is underlined by my publications, many of them in collaboration with distinguished scientists throughout the country, in Europe or the United States. The real value of studies and research projects stands out that all problems were investigated by both a hypothetical approach with numerical simulations and the experimental part, confirming the theoretical results.

In 1994, I founded together with a group of fellow experts, the private company CRIOMEC SA Galati, where I was transferred in 1999 to the position of CEO and chairman (I am holding this position also in the present). This company has as main activity: design, manufacture, installation and repair of industrial plants, cryogenic, petrochemical and metallurgical.

I am a member in academies, organizations, prestigious association, national and international organizations that have membership in education and research.

Raising standards of academic excellence will be constantly pursued and promoted in the great family of our university: students, teachers, researchers and support staff, actively involved me all initiatives to increase the importance and visibility of the University staff.

Brașov, Prof. eng. Alexandru ȘERBAN PhD

July 2016

Scientific and professional achievements and the evolution and development plans for career development

The current habilitation thesis makes a synthesis of the research activity done by the candidate and the obtained results. Habilitation Thesis on "Cryopreservation at constant volume" presents the main concerns of scientific, professional and research that I conducted after completion of the Doctoral Thesis in the field of Mechanical Engineering, 2004 (diploma Series D, no. Minister 0003843, based on Minister of Education and Research Order no. 5237 of 05.11.2004), up to now, highlighting in the same time, the work done after obtaining the title of Professor (2014) and so far, especially my current concerns.

Refrigeration systems have an prominent role in our everyday life. Most of the systems are used in food preservation, air conditioning for comfort, medical applications, special construction works, ice rinks etc. In recent years, environmental aspects have been an important issue in designing and development of refrigeration systems. Another important aspect is related to reducing the size of the devices, to lower the power consumption for a specific cooling capacity.

Cryogenics, the science of temperatures lower than -50șC, play a major role in medical purposes, especially in cryosurgery and cryobiology, space technology and in cooling electronics, that are mainly part of supercomputers.

Scientific and professional achievements (min. 150000 characters)

My research is focused on the following five areas:

The study of processes and systems used in air conditioning, comfort and technological refrigeration;

The study of processes, systems and materials used in Cryogenics;

The study of heat and mass transfer in buildings and building services;

Analysis and evaluation of renewable-energy sources potential in our country;

Applications of refrigeration and cryogenics in Bioengineering;

The study of processes and systems used in air conditioning, comfort and technological refrigeration

In Romania, it’s topical the comfort cooling of small volumes, like offices, holiday homes, individual residential suites or luxury apartments, that require small values of air conditioning power ranging from 5 kW up to 50-60 kW. Cooling power is about 15-20 W/m3, in areas corresponding to a microclimate for human comfort. Cooling systems for air conditioning are direct cooling and indirect cooling. In direct cooling systems, the air is coming into contact the evaporator surface, this solution being accepted when we have a single consumer, with a unique microclimate, cooling power controls being difficult. Indirect cooling systems are those where air is conditioned using cold water produced by cooling machines. These last systems are more flexible, providing air conditioning for consumers with distinct microclimate conditions. There are currently direct cooling systems, VRV types, high tech, working in heat pump mode, which do multi-room air conditioning with different microclimates, for example, up to 6-8 spaces, cooling power being around 30 kW. Where imposed, chiller type systems can produce chilled water for air conditioning purposes. Refrigeration machines used to this purpose are mechanical vapor compression machines and sorption machines, absorption and adsorption ones.

On the Romanian market are distributed more mechanical vapor compression machines but were imposed also absorption machines, considering the possibility of using the latest renewable and recoverable energy.

Absorption refrigerating systems are used with ammonia-water solution, small power lithiumbromide-water solution systems, as Japanese manufacturing systems or Chinese's manufacturing.

Research in Romania was focused for a long period of time on the improvement of the absorption systems using renewable and recoverable energy. The research groups from the Department of Heat Engineering and Thermal Devices from UTCB and more recently Building Services Department from Transylvania University from Brasov have been involved in such researches. It must be pointed out the recent Solar Cooling System of 17,5 kW, with a LithiumBromide-water machine, bivalent driven, by solar hot water and/or with hot water prepared with a conventional boiler and compaction research related to ammonia-water machines using heat exchangers with microchannels, driven by renewable energy and recoverable developed by UTCB, UNITBV and CRIOMEC SA. The latest research on ammonia-water absorption machines, small power, with compact heat exchangers, powered by renewable energy are listed below.

Small power refrigeration cooling systems with ammonia-water solution

Complex HVAC system, using two ammonia absorption systems from UNITBV

The Transylvania University Building Services Department has completed and operates a complex HVAC system for cooling and heating of indoor spaces through the interconnection of two ammonia-water absorption systems manufactured by an Italian company.

Both equipments have been placed upon a platform outside the building. This way, the chiller fan noise (57 dB) and accidental ammonia contamination are avoided. The chiller is operated as refrigeration machine, and the heat pump can be operated in a reversible mode as a chiller or as a heater using heat energy to provide cooling or heating. Both equipments are interconnected supplying with chilled or warm water the fan coils located within the faculty rooms depending on the seasonal requirements. The absorption heat pump is preparing warm water up to 60 șC recovering heat from the outside air. The ammonia is the refrigerant being absorbed by the water – the absorption fluid. For the balancing of the water circuits, a hydraulic separator is used. The nominal temperature of the chilled water is 7.2°C returning back to the unit with 12.7°C for an outside air temperature of 35șC. The rest of the equipment, circulation pumps, accumulators, filters, and the electrical wiring, direct measuring devices, and the loggers for the acquisition of data provided by the sensor are located in the adjacent room.

Two absorption machines single-effect gas fired, one operating only as a chiller and the other, reversible, working as a chiller or as a heat pump are connected as shown in Fig. 1.

Fig. 1. Small capacity ammonia-water absorption systems at Civil Engineering Faculty Brașov

The chiller is an AYF 60-119/4 standard version having a cooling capacity of 17.49 kW at a nominal chilled water flow of 2735 l/h and a gas consumption of 2.51 m3/h. The maximal sound pressure level is 57 dB(A). The complementary heating module supplying 2000 l/h of domestic hot water can be operated in both heating and cooling seasons. It has a capacity of 32.5 kW and is provided with a storage tank installed in the inside vicinity. To avoid the danger of possible freezing during the heating season the circuit between the heating module and the storage tank is filled with antifreeze solution.

The chilled water at 7șC provided by the chiller and by the heat pump operated as a chiller too is pumped into the fan coils placed inside the rooms. As a result, the inside air is cooled and dried and the water returns warmer at approx. 12șC to the refrigeration units.

The GAHP-AR type heat pump has a heating capacity of 35.2 kW for a thermal input of 25.2 kW. Its cooling capacity (in the reversible operation mode) is 16.9 kW. The unit recuperates 54 kW from the ambient air for every 100 kW resulting from the natural gas burned inside the equipment. The 144 kW heating capacity resulted is accompanied with a flue loss of 10 kW.

During the heating season the heat pump supplies the above mentioned fan-coils with warm water having a maximum temperature of 60 șC even at negative ambient-air temperatures, i.e. -20șC. However, the heating performance is affected by the outside dry bulb temperature and also by the hot-water temperature leaving the unit. This installation (Fig. 2) was realized to be used in different research studies at doctoral and Msc level, but it is also useful for testing activities (AHU, cooling rooms, hydronic coils for heating/cooling, radiators).

Fig. 2. Hydraulic setup and component denomination

LEGEND: R1 – Robur AFY-60-119 – Air cooled ammonia-water absorption chiller-heater, gas fired, cooling capacity =17,7 kW, heating capacity =32,5 kW.

R2 – Robur GAPH-AR – Reversible gas fired, air cooled ammonia-water, absorption heat pump, cooling capacity =16,9 kW, heating capacity =35,3 kW

Absorption chiller with ammonia-water solution and compact heat exchangers

Fig. 3 illustrates schematically the major components of the ammonia-water refrigeration system prototype connected to solar collectors, designed to produce cold water 7/12 șC for air conditioning. At first seen we might say that the diagram is typical for such a system, which is not wrong, but some key components are different. The two economizers, the generator and the evaporator are plate heat exchangers and the condenser, together with the absorber are finned minichannels heat exchangers, air cooled.

Working principle

Water cooling system is a solar device with ammonia-water solution, operating on the principle of absorption and is calculated for approximately 5 kW. Hot water, 85-90șC prepared by solar collectors SC, is used by the generator for boiling ammonia-water solution.

Fig. 3. Solar cooling installation using an ammonia-water solution prototype cooling machine. Scheme.

G – generator; LS – liquid separator; C – condenser; E2 – subcooler (economizer 2); CV1, CV2 – control valves 1,2; V – evaporator; A – absorber; E1 – economizer 1; SC – solar collectors; R – hot water tank; P – circulating pumps; Ps – solution pump; Co – consumer.

The generator G is a plate heat exchanger. After boiling, is resulting in a biphasic solution, constituted by poor solution and ammonia vapors, which are separated in the liquid separator SL, from where they go to the condenser C, consisting in 1,5 mm minichanels, fined heat exchanger, air cooled. Ammonia condenses in the condenser C and the resulting liquid fall in the subcooler E2 where is subcooled, then laminated by the control valve CV2, after which the liquid enters the evaporator E. Here, the liquid ammonia vaporizes, by taking from the cooled water, which comes with 12șC. Vapors enter the subcooler E2 being preheated and then being absorbed in the absorber A, by weak ammonia solution.

The result is a strong ammonia solution, which is heated in the economizer E1 then being pumped into the generator G by the solution pump PS. The weak solution, poor in ammonia resulting in the generator G, is separated into liquid separator LS is cooled in the economizer E1, then laminated by the control valve CV1 and finally absorbed in absorber A, where a strong ammonia-water solution is formed.

A first machine was developed (see Fig. 4) using plate heat exchangers resistant to 21 bars and a multistage high pressure centrifugal pump. In the summer of 2011, when the operational test ware made, one of the heat exchangers yielded since the pressure throughout the system increased more than the maximum allowed. During these tests, we managed to get a cooling effect on evaporator, but inlet/outlet inlet/outlet temperature difference in the water circuit did not change.

After the failure incident, modern heat exchangers have been ordered to withstand the pressure of 30 bar and also new fans have been ordered for the condenser and absorber in order to obtain a higher thermal efficiency.

Fig. 4. First cooling machine prototype

In 2012, we have realized a new machine (see Fig. 5) with the new 30 bar resistant plate heat exchangers, new fans and also on each circuit were installed temperature sensors that send signals to a data acquisition and measurement system. Equipment sizes calculated for this new machine are presented in Table 1:

Table 1. New machine heat exchanger sufaces

As can be seen from Fig. 5 improvements and additions have been made to be sure this time we will be able to make it work.

Fig. 5. Second ammonia-water absorption cooling machine prototype

Water cooling system is a solar installation with ammonia-water solution, operating under the principle of absorption and is calculated for approximately 5 kW, as can be seen in Table 2. Hot water prepared by solar collectors, with temperature between 85-90oC is used in the generator for boiling the ammonia-water solution.

The vapor Generator consists of mini channels, with dimensions of 2×1 mm2, construction material is aluminum. The absorber is an original construction, consisting of mini/micro channels, arranged in two vertical rows and have efficient finned outer surface, with a superior distributor for the poor solution and lower collector for the strong solution; ammonia vapor injection, to be absorbed is done through the median distributor, connected to the mini/micro channels by individual connections. Evaporator has the equivalent construction as the vapor generator and is from the same material. The economizers are the same type of construction as the generator and evaporator. The condenser is constructed of micro / mini channels, with efficient finned outer surface. The condenser is air cooled.

The geometries for main plant equipment are given below, in Fig. 6, Fig. 7 and Fig. 8.

Fig. 6. The Absorber

Table 2. Parameters values for equipment sizing

Fig. 7. Heat exchanger used as Evaporator and Vapor Generator

Fig. 8. The Condenser

The use of heat exchangers with micro/mini channels in absorption refrigeration systems offers the possibility of low refrigerant charges as well as high-heat transfer and compact design. Parts that are difficult for small refrigeration systems with powers of 2-10 kW are absorber and the ammonia-water solution pump. The presented system was tested using an original construction absorber with micro/mini channels of 1.5 mm equivalent diameter, which had good results, and the system produced cold. In this stage were obtained in the evaporator vaporization temperatures, positive, producing chilled water for comfort air conditioning. At these low cooling power can be made mobile refrigeration systems, that can use conventional energy, renewable (solar, geothermal) and recoverable, such as the hot gas fluids. Coefficient of performance calculated, COP of the system is around 0.6.

An important addition and improvement in the system, last year, was the automation which helped us see all temperatures in every part of the system with very high accuracy. Data acquisition and measurement system, ISU-MMC-24C, consist of a multichannel recorder with up to 24 inputs galvanically separated, with relay, serial and Ethernet communication (Modbus TCP/IP and Modbus), thermocouple inputs, resistor thermal detector RTD, unified signal, local display to show measured values and offline recording [1], [2].

Fig. 9. Data acquisition and measurement system

Solar driven ammonia-water absorption chiller, modified from gas heated generator in warm water heated generator

A gas fired absorption system having a 17.5 kW refrigeration capacity was modified by replacing the vapor generator with a plate heat exchanger that boils the ammonia-water solution by means of solar heated water. The rest of the system is kept in its original form. Fig. 10 shows the modified system.

Fig. 10. Image of heat exchanger mounted as steam generator

The Generator consisting of a plate heat exchanger of 30 kW corresponds to the nominal cooling power of 17,5 kW (that requires about 29 kW).

The modified adsorption chiller is not controlled by any automation system, it has a continuous function and from this fact result the small-time variations of the afferent parameters.

Presentation of these systems represents a call to the specialists also to promote cooling and air-conditioning systems. Concerned about the introduction of new natural refrigerants and new refrigeration systems government, international institutions such as UNEP, IIR, and the Council of Europe adopt measures to amend the standards and norms of design, construction and operation of refrigeration, heat pumps and air-conditioning systems. In developed countries, companies have switched to using natural refrigerants and cooling systems that use renewable and recoverable energy sources, instead of transition refrigerants and classical cooling systems.

In our country, professional and scientific societies should contribute to change internal rules designed to protect the environment and conserve the energy [1], [2].

Adsorption cooling

Adsorption (also called “solid sorption”) refrigeration systems use solid sorption material such as silica gel and zeolite to produce cooling effect. These systems are attracting increasing attention because they can be activated by low-grade thermal energy and use refrigerants having zero ozone depletion potential and low global warming potential. The adsorption refrigeration system has several advantages compared with the absorption refrigeration system [3] (white range of operating temperatures, no crystallization issue, suitability for applications where no vibrations are needed).

The commonly used physical adsorbents for adsorption refrigeration systems are activated carbon, silica gel and zeolite (Fig. 11) [4].

(a) (b) (c)

Fig. 11. Commonly adsorpents: Silica-gel (a), Zeolite (b) and Activated Carbon

Fig. 12. Schematic Adsorption chilling water system

A1/G2; G1/A2 – adsorber/generator; C – condenser; E – economizer; V – evaporator; VR – control valve

Adsorption refrigerating machine belongs to the family of sorption machines, which unlike absorption machines, use a solid absorbent instead of one in liquid form. Desiccant refrigeration systems began to be used more intensively starting with the energy crisis and environmental concerns by removing refrigerants CFC and HCFC family. Need for energy conservation has generated the use of renewable energy sources (solar, geothermal, wind energy, etc.) as well as the energy sources of low temperature. Adsorption refrigerating machines represent a viable solution for the use of these resources. At the same time, adsorption systems use natural refrigerants, which protects the environment. Fig. 12 shows a schematic diagram of this machine and Fig. 13 shows a functional scheme that incorporates an adsorption refrigeration system.

Fig. 13. Functional scheme of adsorption refrigerating machines

LEGEND

A1/G2 – adsorber/generator; RAC – hot water tank; G1/A2 – generator/adsorber;

K – boiler; C – condenser; TR – cooling tower; V – vaporizer; P –circulation pumps;

E – economizors; AHU – fancoils; CS – solar collectors; AC – conditioned air;

Working Principle

PERIOD 1: The generator G1 has a rich surface in vapor refrigerant, ammonia and heating with a heating medium, hot water from solar collectors / boiler, having a temperature of 80-90 °C, the ammonia vapor is released and moves to condenser C. In condenser the vapor condenses, resulting a subcooled liquid into economizer E and then laminated in VR adjustment valve. After lamination, the fluid enters the evaporator, where it evaporates and the cooling water prepared is used for air conditioning in the AHU. The resulting vapor is adsorbed to the absorber surface A1, the heat of adsorption being taken over by a cooling water circuit, coming from the cooling tower TR. The condenser is cooled with recirculated water at the cooling tower TR.

PERIOD 2: Adsorber A1 becomes generator G1, and the generator G2 becomes A2. Operation is identical to that in PERIOD 1.

Compared with liquid absorbent refrigerated car, car desiccant has wide range, from 50 șC to 500 șC. They do not use circulators and grinding systems vapor corrosion processes does not occur and are not sensitive to shocks and different fixtures. Because last qualities can be applied to cooling in locomotives, buses, boats, spacecraft. Disadvantages in COP cold reduced and low specific power.

These disadvantages can be overcome by enhancing heat and mass transfer in the adsorbent and the choice of adsorbent-adsorbed couples with favorable adsorption properties.

Desiccant refrigeration systems operated by solar energy or renewable energy sources can be used to obtain small and medium refrigeration power. Compared with liquid absorption refrigeration machines, the machine has a wide range desiccant, from 50șC to 500șC. They do not use circulators and grinding systems vapor corrosion processes do not occur and are not sensitive to shocks and different fixtures. Because of the last qualities, this technology can be applied to cooling in locomotives, buses, boats, spacecraft [4].

Evaporative cooling

The principle underlying evaporative cooling is the fact that water must have heat applied to it to change from a liquid to a vapor. When evaporation occurs, this heat is taken from the water that remains in the liquid state, resulting in a cooled liquid.

Evaporative cooling systems use the same principle as perspiration to provide cooling for machinery and buildings. A cooling tower is a heat-rejection device, which discharges warm air from the cooling tower to the atmosphere through the cooling of water. In the HVAC industry, the term “cooling tower” is used to describe both open- and closed-circuit heat-rejection equipment [5].

When considering water evaporating into air, the wet-bulb temperature, as compared to the air's dry-bulb temperature, is a measure of the potential for evaporative cooling. The dry and wet bulb temperature can be used to calculate the relative humidity.

Evaporation will take place when the humidity is below 100%, and the air begins to absorb water. Any given volume of air can hold a certain amount of water vapor and the degree of absorption will depend on the amount it is already holding.

The term humidity describes how much water is already in the air; relative to the amount it is capable of holding. Air is saturated when it cannot hold any more water. Imagine it as a sponge, if the sponge held half as much water as it was capable of holding, it would be 50% saturated. In the case of air, we would describe the Relative Humidity as being 50%.

Energy is required to change water from liquid to vapor. This energy is obtained in an adiabatic process from the air itself. Air entering an evaporative air cooler gives up heat energy to evaporate water. During this process, the dry bulb temperature as the air passing through the cooler is lowered [6].

(a) (b)

Fig. 14. Open coling tower (a) and evaporative cooling unit (b)

SOLUTIONS COMPARISON

Table 3. A brief description and a technology comparison of the cooling/air conditioning systems in the paper with prior to cost/complexity and technical maturity.

Use of natural refrigerants

Legislation on fluorinated gases and alternatives

Climate change is an alarming global problem. The melting of polar ice and glaciers, is rising sea levels and ribs whole under threat are some of the major issues that were triggered during this time, and we will try to fight a long period. Other important consequences include extreme temperature values, species extinction, droughts, floods or gaps in food production. The atmosphere immediately responds to global warming induced by humans, and the consequences are affecting the economy and society. The Kyoto Protocol is the first binding international agreement, that imposed several industrialized countries to reduce greenhouse-gas emissions. The main objective is to reduce emissions of CO2 from burning fossil fuels such as coal, oil and natural gas. However, we need more ambitious commitments in order to avoid the disasters which threaten people and the environment. Catastrophic economic and ecological consequences are predictable in case of exceeding 2 șC warming. Immediate action to halve greenhouse gas emissions of greenhouse must be taken globally by 2050 if we are to limit global warming to 2 șC. To do this, it is not enough to focus on preventing carbon dioxide emissions, but also to follow the Kyoto Protocol to reduce the use of fluorinated gases.

If the Montreal Protocol, lasted 13 years from the discovery made by scientists to be translated into political action. In September 2007, they were celebrating the 20th anniversary of the signing of the Montreal Protocol, regarding substances that contribute to ozone depletion. The Montreal Protocol has sparked innovative unequaled progress through intermediate stages, including alternative substances and processes that may have a negative impact on the ozone layer.

The next stage will focus on reducing the climate impact of these alternatives imposed by the Montreal Protocol.

The challenges of the Montreal Protocol, we will face to include:

Managing existing stocks of substances that contribute to ozone depletion;

Dealing with the use of substances currently exempted and the need for critical moments;

Decreased use of HCFC substances and expedite the removal process;

Maintaining expertise and momentum, combating illegal trade and ensuring the successful implementation and compliance;

Evaluation costs, efficiency and funding issue unresolved;

Interaction with other agreements and environmental issues.

A key element in the international effort to protect the environment is the successful cooperation to achieve the common goal.

Ammonia

Ammonia has been used for industrial applications since 1930 and is generally recognized as the most effective refrigerant. It has a low boiling point and is favored because it is a refrigerant efficient energy, which is also environmentally friendly, with zero ODP (Ozone Depletion Potential – the potential damage to the ozone layer) and zero GWP (Global Warming Potential).

Ammonia is a chemical that consists of a nitrogen atom and three hydrogen atoms. Chemical notation is ammonia NH3, and the name used in cooling devices is R717. Ammonia is highly soluble in water and is commonly used in refrigeration systems with ammonia-water absorption, where it forms an ammonia-water solution, where ammonia is the refrigerant and water is the absorbent. The ammonia is combined with water to form ammonium hydroxide.

Ammonia as a refrigerant has four big advantages over synthetic refrigerants:

An ammonia refrigeration system can cost less because of the small mass flow which causes using smaller pipe diameters;

Ammonia is 3-10% more efficient than some synthetic refrigerants, so that an ammonia refrigeration system consumes less power, resulting in lower operating costs;

Ammonia is a natural refrigerant that does not contribute to the deterioration of the ozone layer and global warming;

It is substantially less expensive than synthetic refrigerants.

Of course, there are two major disadvantages:

Ammonia is not compatible with copper;

Ammonia is toxic in high concentrations, but has a specific smell and can be quickly and easily identified and being lighter than air, rises and dissipates into the atmosphere.

Carbon dioxide

Carbon dioxide is not a newly introduced refrigerant, which is used since the nineteenth century, reaching a peak in 1920. Its use has decreased due to the emergence of synthetic refrigerants, which has the advantage that can be used at lower pressures. Basically, this disadvantage is the biggest challenge in using carbon dioxide as the refrigerant: relatively high pressures of work.

Carbon dioxide CO2 is the chemical formula and consists of a carbon atom and two oxygen, and the name into the field of refrigeration is R744.

Carbon dioxide has the following advantages in use as a refrigerant:

It is very abundant in the environment;

Present as waste is in many cases resulting from technological processes;

Available everywhere, and its recovery installations foregone is not required;

Being a natural refrigerant not adversely affects the earth's atmosphere, but it is certainly a greenhouse gas;

It is an inert gas, compatible with all materials (plastic, metal or elastomers) used in refrigeration;

Safety in working with natural refrigerants

Safety is one of the major concerns when using a specific refrigerant, due to risks related to toxicity, mechanical damage, overpressure, asphyxiation, etc. The use of synthetic refrigerants involves risk resulting from flammability. In general terms, this risk is handled in compliance with safety standards and regulations. However, improvements in safety can be achieved by examining and analyzing the causes of an ignition event and the potential consequences. Findings from performing an exercise of this type can be used to improve the design, execution and maintenance services and related equipment considered. The principles to be followed to minimize the risk of flammability are:

Reduce the risk of leakage;

Reduce the possibility of accumulation of leaked refrigerant;

Reducing the occurrence of installations from a fire perimeter.

Appropriate safety rules should be implemented:

Training of plant personnel;

Quality control systems used (ISO 9001);

Monitoring and feedback equipment placed into service;

Monitor the reliability of suppliers / components;

Approval procedures for contractors and manufacturers;

Develop test stands for components and assemblies at various operating modes;

Periodic inspections;

The adoption of such safety rules can provide improvements in design, construction and safe operation of refrigeration systems.

Use of natural refrigerants in different applications

There are three main factors that affect the implementation of any refrigerant: they are cost, safety and technological status. In principle, almost any refrigerant can be used in any application. The decision to apply a particular refrigerant validation involves significant risks and eliminates the budget allocated to people.

Usually when it comes to the use of ammonia as a refrigerant is related to a human safety problem due to the high toxicity and if carbon dioxide is connected to the high pressure.

Of course, natural refrigerants can be included in all kinds of applications, such as heat pumps, absorption chillers, Air-conditioning units for low power and high refrigeration, for ice rinks, shopping centers or facilities for cooling server rooms, etc.

A research is widely in progress worldwide, for the application of natural refrigerants in as many areas with promising results, including air-conditioning mobile and residential heat pumps, chillers, commercial and industry marine.

Using ammonia will continue, especially for large industrial systems and larger systems of air conditioning. However, the acute toxicity of ammonia loading limitations suggests that ammonia will be implemented.

After an absence of 50 years, carbon dioxide returned to refrigeration, and its use is growing rapidly. The carbon dioxide will be used as a refrigerant for low-temperature systems in cascade, the refrigerant volatile second in order to avoid high power pumping associated in the movement of the glycol or water cooled and, optionally, a refrigerant directly, but depends on production of adequate refrigeration compressors.

Greenpeace believes that governments should promote the use of natural refrigerants and claim data to eliminate synthetic agents in air conditioning refrigeration systems. These gases must be removed [7].

The study of processes, systems and materials used in Cryogenics

New technologies in the field of air separation

Cryogenics aims at developing and improving techniques for obtaining very low temperatures, processes and equipment. In contrast to the low-temperature physics, cryogenics using technical dealing with phenomena that occur at low temperatures, even with basic scientific research, especially that the two goals, there is no exact dividing line. An engineer should be familiar with the physical phenomena to be able to use them effectively; a physician should be familiar with the principles of engineering to be able to design specific experiments and equipment.

Cryogenic word comes from Greek and means "cold production" in the temperature range -150 to absolute zero.

Air is a mixture of various gases, among which the most important are: nitrogen (N2) 78% by volume, oxygen (O2) and 21% by volume and argon (Ar) 1% by volume.

Most air separation unit produce these three gases in liquid form. Some units produce more oxygen and/or nitrogen gas to be delivered by pipeline to consumers.

Fig. 15. Scheme of an older air separation plant, Russian construction-type Kaar-15

Below is a schematic diagram of a "separation plant air at a low pressure without producing argon" (Fig. 16), followed then by a general description of the technological process, after being detailed technology updates added to air separation units.

Clean compressed air enters the cold tank from the frontal purification system and is cooled to temperatures near its liquefaction about -170șC (-274șF) by blowing cold currents produced in the main heat exchanger. The air then enters the high pressure column (called here "column HP") where it is separated by distillation in nitrogen streams from the top and a stream of liquid containing about 37% enriched oxygen from the bottom.

HP column nitrogen gas from flowing into the main evaporator, where it comes in contact with liquid oxygen and low pressure in the catchment area of ​​low pressure column (called here "column LP"). Boiling liquid oxygen (approximately -179șC or -290șF) against condensing high pressure nitrogen from the HP column provides reflux. The final separation occurs at the LP column, which operates at approx. 1.4 bar (20 psi).

Reflux and supply currents are provided by liquid nitrogen and liquid enriched from HP column. These liquids are in the liquid nitrogen gas against undercooling subcooled prior to being expanded to the LP column.

Fig. 16. Diagram of a modern air separation units (ASU) low pressure, German type [8]

Boiling oxygen, LP column provides the energy needed to extract nitrogen and argon in the liquid stream enriched.

Product gaseous oxygen is taken from the bottom of the LP column and the product pure nitrogen in the top. A residual stream of nitrogen intermediate used for reactivation of the absorber layer is extracted from the top of the LP column. It is usually composed of more than 2% oxygen and argon, which contains virtually all there in the cold tank.

Hydrocarbons were not removed from the frontal air purification facility (EFF) accumulates in the bath liquid oxygen near the main evaporator. To reduce this risk, it can provide a filter filled with liquid oxygen adsorbent (hereinafter, "LOX filter"). (It depends upon the requirement of the process: for example, installation GOX concentration ratio is very low so LOX filter is not needed). Two filters are installed in parallel, with one in the adsorption phase and the other in regeneration.

To maintain proper operating temperature in process and compensate for heat loss from the tank cool, it needs a plant producing cold. Normally, a low-pressure gas system is provided as an expansion turbine plant producing cold. This machine has partially heated nitrogen from the HP column, equal to about 10% of the airflow to cool the tank, and the expansion cools to reach the starting materials. For certain advantages, a small flow of high pressure nitrogen may be heated prior to the other products in the main heat exchanger. In the most-recent installation designed, turbine operates at a low flow of fresh air, which was built in his own pressure compressor (expander-auxiliary).

In the case of high yields of LOX (LIN), there may be a separate liquefaction, a permanent liquid from the liquefaction (or storage when liquefier is turned off).

Air purification

Removing moisture and CO2 is necessary for efficiency and safety operation of air separation units (ASU). If not, humidity and CO2 gas content in the air will be transformed respectively in solid ice or snow CO2, cooled in the air ducts of the exchanger and CO2 may be lodged in the channels of oxygen evaporator mainly leading to some ASU risks in operation.

The goal of Front-end Purification (FEP) is to remove impurities by adsorption by air compression and pre-cooling, because the moisture contained in the air is less at higher pressure and lower temperature according to the Robitzsch tables (relationship between temperature and the maximum amount of water (vapor saturation) in the volume of air).

Adsorption consists of fixing on a solid surface (called adsorbent) molecules in the form of gaseous or liquid. These molecules penetrate the pores having a diameter of several angstroms. Adsorption is a surface phenomenon, reversible, which means penetrated molecules can be removed by heating the adsorbent and then depressurized (resting phase).

Adsorption phenomenon is favored by observing the following factors:

High pressure;

Low temperature;

Small adsorbent particles.

They are considered two different layers of adsorption: the first (according to the direction of air flow) layer of alumina which adsorbs water, the second-layer molecular sieve that adsorbs carbon dioxide, otherwise a small fraction of carbon dioxide is adsorbed by alumina.

Scheme with two layers reduce energy regeneration as if used only molecular sieve, require a greater amount of energy to remove water from the molecular sieve.

The most used technology today is by Thermal Swing Adsorption (TSA), adsorption-desorption cycle: one vessel is in adsorption phase while the other is in a regeneration (Fig. 17.a).

There are two types of containers:

1. Recipients with horizontal adsorbent beds (Fig. 17.b);

2. Recipients of radial adsorbent beds (Fig. 17.c).

(b) (c)

Fig. 17. The sequence of one cycle of purification of the air (a), the container, the adsorbent beds is horizontal (b) and container, with the adsorbent beds vertical (c) sequence of a cycle of purification of the air (a), the container, the adsorbent beds horizontal (b) and container with the vertical adsorbent layers (c)

The adsorbents used to remove water and carbon dioxide from the air based on the temperature swing adsorption are classified according to some code. This code enables products to be identified without damages to the provider.

Recovery heat exchangers

Heat exchangers are one of the main elements that ensure low temperatures and are a necessary part of any installation of deep cold.

Contemporary methods for obtaining low temperatures rely to a considerable extent on the principal regenerator, allowing the accumulation of cold in the system, which is possible only by using heat exchangers. This principle was first realized in 1895 by Linde and Hampson, that liquefied air using countercurrent heat exchanger for accumulation cycle with cold lamination.

The characteristic features of the heat exchangers used in installations for cold deep, is the tendency to ensure a minimum temperature difference at the warm end of the heat exchanger. This difference in temperature is cold, and the loss of a considerable extent determines the size of a facility's energy costs. Another source of energy, linked with the presence of the heat exchanger pressure drop Ap is inevitable the movement flows into the heat exchanger.

Thus, the design of any heat exchanger typically faced with some conflicting requirements, namely the need to ensure minimal differences in temperature to the extreme hot exchanger DT and a minimum pressure drop Dp on the one hand, and the need to achieve a light and compact unit, on the other hand. Ap tend to decrease relates to lowering speeds flows through the machine, which reduces heat transfer coefficients and that increases the heat-transfer surface. Lead to the same result and decrease Dt.

The need to reduce the size and weight that binds heat exchangers large modern cooling installations are quite bulky forwarded weigh tens of tons, are made of copper and its alloys. The optimal ratio between the various parameters of the heat exchanger can be found by choosing the most appropriate form of building concrete conditions and rational design of the device. The whole diversity of forms of construction and types of heat exchangers installations deep cold can be divided into three main groups: a) appliances tubular sheath; b) Spiral heat exchangers; c) effective exchange or compact.

Intensive development of cryogenic technology has greatly increased requirements imposed to heat exchangers. As a result of the considerable increase in the efficiency of the various units and in some cases the need to achieve a small size of construction of the shell and tube exchangers usualy spiral proved to be unsuitable for a number of installations of low temperatures.

In this context, now are developed many forms of construction for efficient heat transfer, some of which are of great perspective.

Heat exchangers are devices for efficient power transfer considerable thermal mass, relatively small overall dimensions and low hydraulic resistance to fluid movement.

There are two main areas that allow heat exchangers increase productivity:

intensifying and upgrading existing types (tubular and sheall-and-coiled);

developing various of new heat transfer surfaces.

The most used type of heat exchangers used in Cryogenics are plate heat exchangers made of a special aluminium. The heat exchange and the main components of such heat exchanger are presented in Fig. 18.

Fig. 18. The structure of plate heat exchanger made of aluminum [8]

Within each layer are ribs which increase the heat transfer surface. They not only increase the heat exchange surface, but also have a structural purpose.

There are several types of ribs for the type of process and fluid characteristics (Fig. 19).

Fig. 19. Types of ribbed aluminum plate exchanger [8]

Mounting plate heat exchangers aluminum means:

Lower surface;

Eliminating switching valves;

The ability to transfer heat between several fluids;

It may use high-pressure equipment. In case of regenerators the pressure can not be greater of 7-8 bar, because it generates default thicknesses and weights too large for the tanks.

Separation

Typically, the components of an air separation unit are lower column, the upper column and the condenser.

This installation lead to:

Weaknesses in start-up facility;

Hydraulic losses between the condenser and in high-pressure column<;

Large areas covered by three enormous reservoirs;

High consumption of expensive materials (austenitic steel, copper, brass, aluminum, etc.).

Fig. 20. The scheme of an old air separation unit with lower column, upper column and condenser

An air separation unit uses distillation for separating the air in its natural components: nitrogen, argon and oxygen. The distillation process realizes this separation by the use of thermodynamic properties that are specific to each component. Enough to debate distillation is necessary to analyze thermodynamic processes and vapor-liquid equilibrium.

A distillation column using sequential steps achieve the desired separation. Fig. 21.a shows the general scheme of a simple distillation column. The levels facilitate the vapor-liquid contact, which causes the elements to condense heavy and light elements to vaporize. Theoretically, vapor and liquid on each level must be in perfect balance.

However, actual distillation levels do not realize the whole mixture in perfect homogeneity. Therefore, a real distillation tower needs multistory than theoretical calculated levels.

The product purity is a direct function of the number of levels in column (several levels, higher purity).

There are two types of levels of the distillation trays and filling. They both show the same interest because they are still used.

The new air separation technologies involve a double column with multiple levels and plate heat exchanger as the condenser (Fig. 21.a).

Fig. 21. Double Column built multi-storey with incorporated condenser (a) and column with packeges (b) [8]

Many air separation plants use the above model as an effective way to produce large amounts of oxygen and pure nitrogen limited quantities [9].

The transition from old technologies to new means:

Reducing the amount of metal (stainless steel) used for the manufacture of equipment;

Reducing the area occupied by the installation;

Increased reliability separation units;

Reduce energy consumption by eliminating the regenerator exhaust into the atmosphere quantities of waste nitrogen, compressed to 7 bars, which cannot be recovered;

Reducing the commissioning period of 6-7 days to one;

impurities removal ratio improved by canceling nitrogen discharge in the atmosphere;

The use of the packed column increases the heat-transfer surface and decreases the total volume of the column.

Obtaining rare gases, neon and helium by fractional distillation

Inert gas discovery was one of the most important moments within the history of science. For the first time in 1868, astronomers used the technique of spectroscopy to investigate the sun's atmosphere. On October 24, 1868, French Academy of Sciences received two communications from Jansen from India and from Lochier London on the discovery in the spectrum of the corona during a solar eclipse, a new line of bright yellow that for starters it was symbolized by D3. In August 1871 Kelvin, said the line D3, hitherto unidentified, is due to a new element, so it is a new substance for which its discoverer proposed name of helium (from the Greek word helios = sun) [10].

Neon was discovered in 1868 by British chemist Sir William Ramsay and Morris M. Traves after they discovered the element krypton.

As krypton, neon was discovered after studying the liquefied air. By passing an electric current through a tube with dilute gas, containing the first fraction fused obtained separation plant and liquefaction of air, there is a beautiful light, orange, due to a new chemical element, gaseous, who was appointed highlight (of the Greek word neos = new) (1898) [10].

World consumption of neon in the coming years will exceed 2·105 m3/year. The main consumers of this gas are industry of electric lamps, laser technology and cosmic technique, as can be seen in Fig. 22 [10].

Fig. 22. The main areas of use for neon [10]

Helium is used to develop superconductivity, a state in which the electrical resistance of the cable is almost zero [10].

Other applications of helium are:

use as propellant gas into the fuel tanks of missiles;

use as working fluid in nuclear reactors;

use in the chromatographic analysis.

Separation of inert gases in the atmosphere is done in several stages.

Consumptions of helium and main areas of application are shown in Fig. 23 [10].

Fig. 23. Helium consumption and the main areas of use [11]

Helium rectification and liquefaction

Helium is also extracted from natural gas by similar processes worldwide. In all cases, cryogenic processes are used. In most cases, natural gas contains certain amounts of nitrogen, and the primary objective of the installation is removing nitrogen from hydrocarbons so that the gas is suitable to be fed into the national grid. Helium is extracted from the plant in the denitrogenating section, as the purge of non-condensable. This gas can be further purified to produce liquid helium. Fig. 24 shows a block diagram of the installation for the purification of natural gas, with a built-in helium recovery unit.

Fig. 24. The block diagram for helium extraction plant

Since the main process is cryogenic, any freezing compound must be removed early in the process. Natural gas from the wellhead will typically contain water and acid gases frequently. When crossing a gas pipeline heavier hydrocarbons can condense and, therefore, the first device that you typically see in a process is condensate separator. Natural gas, which is generally at pressures of 2500 to 5500 kPa is then treated by washing with amine or other sweetening process to reduce the levels of carbon dioxide and hydrogen sulphate. Fractions leading the desulfurization unit are then dried using molecular sieves. They are often required to remove acid gases and waste. The gas clean, dry, is then fed to the cryogenic unit for removal of nitrogen, if necessary, and consequently, to give a non-condensable purge, rich in helium, which can be further treated for the recovery of pure helium.

Natural gas purified with appropriate caloric value is extracted from crude helium separation block and compressed back for the gas grid. Depending on the raw gas composition and conditions, it may be necessary additional refrigeration. This ensures nitrogen cycle through a closed circuit or other compression-expansion cycle.

The crude helium stream is then compressed to a relatively high pressure and fed to a helium purification unit. Liquid helium can then be purified or simply compressed in gas cylinders for distribution to beneficiaries. Crude helium leaves natural gas 'block separation' at a purity of 50-80 mol %, the balance being mainly nitrogen, although some mixtures may be present and methane. A flow diagram of the technological process that occurs in a typical unit of crude helium extraction is shown in Fig. 25.

Fig. 25. The typical crude helium extraction of natural gas with low nitrogen content

Dry natural gas is supplied under a pressure of 2500-5500 kPa and is first cooled in countercurrent with return streams produced in the heat exchanger, E1, to condense the heavier hydrocarbons. The heavier hydrocarbons are separated in V1 and V1 vapors continue to be cooled in the exchanger E2, and expanded to approx. 1400 kPa through the valve JT2. The two resulting phases are separated in V2, is sent to the vapor rectifier K1. Liquids rich in methane K1 and V2 are expanded through the valve JT3 and JT4, respectively, and reheated in E2, in order to ensure a necessary part of the cold process. Heavy hydrocarbon liquids from V1 are expanded in valve JT1, mixed with the treated low pressure gas, E2, E1, and further reheated to ambient temperature, forming the reheated gas product.

The rectification column K1 has a condenser that provides liquid nitrogen reflux washing of V2 vapor, thereby reducing methane content at very low levels. Natural gas often contains low levels of nitrogen and therefore, does not require denitrogenating. Thus, the mixture emanating from the top of the K1 will be mainly 60-70% helium and 30-40% nitrogen, with traces of methane. This crude helium, available at a pressure less than 800 kPa, can then be sent to a helium purification unit.

In unusual cases, where the nitrogen is not present in the carrier gas, helium can be used directly with the waste liquid nitrogen in K1, in order to achieve very low levels of methane. High levels of methane in crude helium can cause issues with freezing in the final stages of purification of helium.

Natural gas containing substantial amounts of nitrogen requires upgrading to make it compatible with the natural-gas network. Crude helium recovery and denitrogenating can be effectively combined into a single process relatively simple when supply conditions are appropriate. Polish natural gas contains 42.75% nitrogen and 0.4% helium. Being available to 5500 kPa, it is the ideal choice in this type of process.

Fig. 26 shows a flow diagram for the production of crude helium, used for this case. After removal of water and heavy hydrocarbons by adsorption, gas is admitted exchanger blades E1 is expanded to about 2700 kPa in JT1, and charged at the base of K1. Methane-rich liquid taken from the bottom of K1, is instantly evaporated to approx. 170 kPa in JT3, and charged to K3. Column K2 is mounted over the column K1 so that the condenser E2, for K1, is actually the reheated for K2, thereby forming the classic double column. The liquid nitrogen is extracted as a secondary stream (side) of K1, evaporated instantly in JT2, and charged as reflux in K2. Liquid methane taken from the K2, is pumped in P1 and reheated in E1, before being passed to the natural-gas network.

A small amount of liquid nitrogen, which is extracted from the side of K1 is evaporated quickly in JT4, and can be used as a refrigerant in final denitrogenating and the process of helium recovery is provided by the expansion of Joule-Thompson valves JT1, JT2 and JT3. Crude helium is extracted from the non-condensable purge product in the condenser E2, passes through a reflux heat exchanger, E3, and returns at the top of the column K1. Then proceed to final purification steps. At this point, the helium is at a purity of over 85%, the remainder being nitrogen. The flow pressure is usually available at approx. 2000 to 2500 kPa and about -190șC. He can be directed towards the helium purification and liquefaction section.

Fig. 26. The typical crude helium extraction of natural gas with a high nitrogen content

Nitrogen regeneration and liquefaction

Neon is recovered mainly using air separation plants, and to make this operation profitable from economic point of view, only large units are taken into account, because neon is present in air only in 18.2 ppm. Since its normal boiling point is much lower than nitrogen or oxygen, neon is not condensed with any of the normal products from the air separation plant. For this reason, it is removed as a purge of inert gas from the upper part of the condenser of the lower column, K2 of a dual column system, as shown in Fig. 27. Without the purging performance of the condenser E1 would be worse because in a certain period of time, Ne and He accumulates in the upper parts of the condenser. In small systems, this inert gas purge is withdrawn periodically, re-heated in the process and discharged through the vent to the atmosphere. The recovery becomes economic in larger installations. Neon commercial scale production began in 1960.

The purge of inert gases may contain about 2.1% neon, 0.8% He and the balance nitrogen, with traces of hydrogen and oxygen. Purge flow is controlled and directed by JT1 in V3, where it is cooled in E2 (inside V3) with liquid nitrogen at a low pressure.

Nitrogen is condensed primarily in E2, returns to V3, and by gravity returns to K2. While maintaining the pressure of the inert gas as much as possible higher, a significant amount of nitrogen is condensed and leaves the crude mixture by Ne + He with the following composition (v/v): 46% of Ne, 19% He, 33% N2, 2% H2 and traces of oxygen. Refrigerant liquid nitrogen is supplied to E2 by JT2 a partial extraction of primary reflux K1 before the sub-cooler E3.

Fig. 27. A system of purification of the nitrogen flow containing neon and helium

The crude mixture is then reheated Ne+He and passed in the final purification and upgrading process, as shown in Fig. 27. In this process, hydrogen is first removed by catalytic combustion with oxygen in W1 and after cooling and drying in E1 and W2, the gas is cooled by liquid nitrogen in V1. A low-temperature adsorber from V1 removes excess nitrogen and oxygen, by bringing the impurities to approx. 1%. A second layer (not shown) reduces more impurities, leaving approx. 71% Ne and 29% He. This stream is then cooled in a hydrogen liquefaction cycle closed-circuit W3. Initial cooling is done in E2, and E3 then condenses a substantial part of neon, leaving vapor containing only 20% neon and 80% helium. They can be heated in the E2 and processed elsewhere, or simply vented. Normally, it is not economical to recover helium from this flow of ventilation because there are many natural-gas streams that are preferred for helium recovery.

Neon product leaves the unit at a purity of approx. 99.99% by volume, as a liquid, which may be bottled or stored at high pressure in the Dewar vessels. Recovery of neon in the process shown in Fig. 28 is more than 95% [12], [13].

Fig. 28. Purification and liquefaction neon unit

Noble gases having the lower normal boiling temperature, neon and helium, may be obtained either as a mixture or in a pure form only from the atmospheric air. These rare gases have a special importance in many technologies and therefore, are expected a significant increase in demand for neon and helium. The most important field of use for these gases is and will be the aeronautic industry because there are no alternatives to their use [10].

Properties and applications of helium and neon

Most regeneration processes are related to other rare gases cryogenic processes, either because major manufacturing a product or because it requires a special cryogenic procedure to reach the point where it can recover the rare gas. By 'rare' can be understood as 'hard to find' or very low concentration. All gases under consideration are usually present in the air and recovered from it. It should be noted that, concentrations are actually lower: 0.934% argon; 18 v.p.m neon; Krypton 1.1 v.p.m; Xenon 0.08 v.p.m. and helium 5.3. v.p.m. Only helium is generally recovered from natural gas, since it is present at higher concentrations (typically from 0.04 to 2%, depending upon the source) [12].

Helium is produced in large amounts by extraction from natural gas, but can get along with neon and fractional distillation of air. In both cases, the two rare gases must be separated from nitrogen by specific cryogenic processes. These gases can be purified after separation in order to bring them in the liquid state.

Characteristics and properties of helium and neon

Helium

Inert gas helium is very, very light and penetrating and for this reason, it is used in a variety of applications in which these properties are exploited. For example, helium as a gas used in welding, diving, balloon flight, medicine, leak detection, and gas chromatography. Helium technical data are presented in Table 4.

Table 4. Properties of Helium

The armed forces were users of helium from the first quarter of the twentieth century, and that was the cause of his production on a commercial scale. Helium was primarily used for filling balloons and airships for surveillance. Smaller amounts were used in diving equipment, and helium began only in 1930 to be used in welding. In USA, helium has been used almost exclusively (99%) of federal establishments, until 1946. Subsequently, as quality producers improved from 98.5 to 99% and then 99.5% more users became interested in helium. In the 50s ballistic missiles and space flight programs in the US have increased dramatically demand for helium. This time approaching 100% purity, further enhancing the number of users. Vapor discharge tubes in vacuum containing He, has an orange color light as shown in Fig. 29.

Fig. 29. Tubes with Helium shaped as chemical element symbol [14].

The limited resources of natural gas and helium rapid growth in demand has given rise to a helium conservation program initiated by the US federal government. This program was initiated in September 1960 and has led many companies to store helium underground, where production exceeded demand. The reason for this was that in many cases the primary objective of a cryogenic separation unit was producing methane rich gas with an energy value corresponding to the amount given. If crude gas was rich in helium gas, the plant would produce lower gas rich in helium, which can be further processed to purify helium. If the entire quantity of gas below (escape) was treated to produce helium exceeded local demand. Therefore, only the required amount was processed, and the remaining gas rich in helium on bottom was either back compressed into the pit, or stored elsewhere underground. Europe has been an importer of helium from the US for several years and its own resources does not appear to exceed demand in the near future. Diving equipment industry uses mixtures of oxygen and helium cylinders for breathing equipment. If using compressed air instead of this mixture, the blood absorbs significant amounts of nitrogen, when the sinking is done at moderate depths. When the diver rises to the surface, desorption of nitrogen bubbles in the blood causes excessively painful and sometimes fatal diver. Helium is much less soluble in blood, so divers can descend to greater depths using mixtures of oxygen and helium. Breathing these mixtures lead to a hazardous phenomenon – the voice changes diver acquiring a much higher tone. This happens because of low molecular weight and frequency of the vocal chords acquired in an environment rich in helium.

Welding industry uses helium as a shielding gas for welding applications specific to aluminum and stainless steel. Helium is used in similar situations with argon as a shielding gas in welding with non-consumable electrode.

Also, many elements and alloys become superconductive at low temperatures well defined. The disappearance of electrical resistance and the emergence perfect diamagnetism is very attractive for superconductive electronic technology in engine design and frictionless bearings. Diamagnetism or perfect magnetic insulation, known as the Meissner effect occurs if the magnetic field inside the material is expelled, when it becomes superconductive. Helium is commonly used as a cooling medium for engines superconducting magnets. They are often used in atomic physics research establishments. It also envisages the use of superconducting magnets in the electric power industry. This is clearly a very specialized helium, which uses the liquid.

A major growth sector for the use of helium in the 80s, is Magnetic resonance imaging (MRI) scanners in diagnostics for the human body. Here, liquid helium is used to cool the superconducting magnets. Recent advances within the field of ceramic superconductive material that does not require liquid helium temperature, might moderate its use.

Helium is also used in medicine to diagnose deficiencies and lung disorders. Helium-oxygen mixtures are used to check blockages in the airways and lungs to check air distribution in the lungs. Although related in terms of quality mixture with diving equipment industry, the amount used in medicine is much smaller.

Because helium gas is very penetrating, that diffuses through very small spaces or cracks, it is often used for equipment leaks in chemical plants. Halogenated hydrocarbons are also used to this purpose, but helium is considered to be the best for this application. Helium is also used in laboratories as a reference gas in chromatography. For this application, is required very pure helium.

Manned balloons, hot air and hydrogen were raised to the air for the first time in 1783, and transatlantic passenger flights have become regular in 1910 and 1920. In 1930 the British airship R101 exploded and in 1937 another bigger Zeppelin Hindenburg caught fire during an electrical storm in New Jersey, and exploded. Heavy loss of life marked the end of regular flights with airships. Hindenburg was filled with hydrogen cheaper, which maintains its buoyancy with very low molecular weight, 2, and the explosion marked the end of balloons filled with hydrogen for manned flights. Since then, many enthusiasts have come up with safer balloons, hot air and many reduced commercial loads. Specialists from weather forecasting institutions continued to use balloons filled with helium to launch electronic equipment at high altitudes, but only between 1970 and 1980 increased interest in the much larger airships.

Helium contained in all modern airships are mainly used for surveillance by military institutions and in advertising. The advertising has grown in popularity because balloons are very large and very cheap. Advertising slogans are painted on the hull greater buoyancy, filled with helium. The balloons are filled with helium relatively easily and after several weeks of use, air balloons penetrate the skin reducing its buoyancy. Helium can then be replaced, or a more economical way it can be re-purified through a process with a semi-permeable membrane, thus restoring buoyancy helium balloon without buying. This operation was started by Airship Industries in England in 1948 and continues to be an economical method of regenerating helium [12].

2.2. Neon

This gas, Neon was named after the Greek word neos, which means "new". It is a colorless and odorless gas that does not react with any substance. The first use was as a medium of neon gas in fluorescent lighting, with the arrival range of 'light band' in 1920. In a vapor discharge tube, in vacuum, neon gives an orange-red light, as shown in Fig. 30. Only this color lamp contains pure neon. Neon liquid is used as a refrigerant in cryogenic plants. The capacity of the cooling system is 40 times higher than that of liquid helium and three times higher than that of liquid hydrogen. More recently, neon began to be used in high-energy physics. In search of subatomic particles, physicists use bubble chambers filled with liquid hydrogen, the core of which is a target. Big accelerators are used for designing atomic particles in the target area, hoping appearance of interesting reactions in the collision target [12]. The technical data of neon are shown in Table 5.

Table 5. Properties of Neon

Fig. 30. Tubes with Neon shaped as chemical element symbol [15].

Noble gases having the lower normal boiling temperatures, neon and helium, may be obtained either as a mixture or in the pure form only in the atmospheric air. These rare gases have a special importance in many technologies, and therefore, it is expected a significant increase in demand for neon and helium. The most important field of use of these gases is and will be the airline industry because their alternatives to their use. In the coming, decade is expected steady growth in the consumption of neon gas and liquid form. Due to the unique properties (low boiling point, low density, low solubility, high thermal conductivity) areas of applicability of helium try to exploit these properties. Helium gas was first used to fill weather balloons and airships. One embodiment uses a helium is the inert atmosphere in the case of electrical welding. However, the wider use of helium in very low temperatures. World consumption of neon in the coming years will exceed 2·105 m3/year. The main consumers of this gas are industry electric lamps, laser technology and cosmic technique [10].

The study of heat and mass transfer in buildings and building services

Testing laboratory using renewable sources for radiant heating & cooling

There are a lot of different ways we can heat/cool a house. Though there are huge differences in individual approach and ultimate efficiency, pretty much all systems fall under two categories: Radiant Heating/Cooling and Convective Heating/Cooling. Radiant heat transfer is the transfer of heat from a heated surface and Convective heat transfer is the movement of heat due to fluid movement. Radiant heat transfer is the transfer of heat from a heated surface involving the electromagnetic waves as the carrier of energy. In case of the convective heat transfer, the energy carrier is a moving fluid in contact with a solid surface.

While in case of convection heating/cooling a larger temperature difference is needed, and the airflow gives different “sensations” at different locations, the radiant surfaces have been recognized as energy-efficient and comfortable systems for sensible heating but for sensible cooling too.

Applying radiant systems for heating/cooling, the heat transfer is done not only through radiation but through convection too as a result that heated air is rising thus providing relatively even temperature distribution in the vertical plane. This is true for ceiling panels, used for cooling.

The structure of the radiant surfaces laboratory, from the Faculty of Civil Engineering

To improve, the undergraduate and master students' knowledge enrolled in Building Serivces Department, a "Radiant Surfaces Laboratory" was designed and built in an unused space in a room placed in the basement of our Faculty (see Fig. 31).

Fig. 31. The absorption GAHP together with the AYF (left). General Assembly System (center). The mechanical compression heat pump (right). Radiant Surfaces Laboratory (in the lower part)

First system installed consisting of a heat pump, a vertical on the floor-mounted fan-coil, water tanks, pumps, a plate heat exchanger, all of them being installed to study the capability of recovering the excess heat from different rooms in order to heat another one and also for preparing domestic hot water used in our Faculty. Of course, it was used for the educational purpose too.

The absorption heat pump and the chiller AFY were the next installed being used for cooling of some computer labs, offices to maintain the interior comfort to establish the operating range for thermal comfort in different conditions. As we said before, all this equipment represents operational teaching materials.

The Radiant Surfaces Laboratory is the latest lab, being composed from four different floor surfaces. A ceiling radiant surfaces are prepared for the next future. For research, we have installed a vertical floor standing fan-coil so that a thermal balance inside the room could be maintained: the mechanical compression heat pump is used for heating through the fan coil and the gas driven absorption chiller/reversible heat pump supplying the necessary cooling by means of the radiant surfaces.

Different hydronic circuits have been installed under-the-floor, on the walls and on the ceiling, the work on the two-last-ones being still in progress.

Because the absorption systems are working at low temperatures, sometimes below zero Celsius degrees, the system is operated with a mixture of 40% glycol. So we had to put another plate heat exchanger before supplying cold agent to the radiant floor and for the fan-coil.

Measurements and evaluation

All facilities are equipped with circuit specific sensors positioned in the control points of the system.

To determine more precisely the heat flow delivered by the heat pump, we have added past year heat meters on the existing installation, on the primary and secondary circuits.

The energy efficiency and thermal performance of different radiant surfaces, different equipment, either we speak about the source (heat pumps with mechanical compression or absorption, chiller, heat exchangers) either about final consumers (fan coil, floor/wall/ceiling radiant panels), are investigated in order to view the electric power consumption, the Coefficient of Performance COP, the indoor comfort parameters and the financial data too.

The measurements include:

surface temperature of floors, walls and ceiling (the coldest point, the hot, medium, DT water / surface);

primary energy supplied in the system, be it electricity or gas;

energy produced by source, compared to the energy absorbed by the source;

aspects of comfort: air speed, air temperature, humidity;

temperature at different heights, surface;

floor temperature correlated with different temperatures of thermal agent.

The data-acquisition system is intended to monitor, display, process and export acquisitioned data, namely temperatures (air temperature indoor &outdoor, surface temperature, etc.) and humidity.

Taking into account the fact that acquisitioned signals are analogical in nature and give significant errors, we have conducted the processing of the signals by numerical – analogical convertors, by conditioning system internal circuits and also by using a state-of-the-art programmable logic controller (PLC) and late generation processing software.

The equipment is able, through the peripherals that it is fitted with to memorize locally the acquisitioned info’s, to display them in real time on the fitted display, but also to transmit them remotely by several connections (Ethernet, profibus, TP-IP) to one or several e-mail addresses via data-transfer protocol FTP and also by web hosting server.

Analysis and evaluation of renewable-energy sources potential in our country

Wind power in Romania

The European Union plays an important role on the international energy market, being the greatest importer and the second largest consumer. Romania’s accession to the European Union on 1 January 2007 has determined significant changes in the energy sector. The changes involved reviewing energy policy, alignment with the EU energy legislation and promotion of renewable and sustainable energy.

There is a widespread interest in reducing energy consumption. Nevertheless, we are undoubtedly witnessing demographic growth (more people have access to energy) and economic development, leading to an increase in energy demand. In 2008, about 81% of the electricity generated on Earth was produced from burning fuels as follows: fossil oil (33.5%), coal (26.8%) and gas (20.9%) [16]. Burning these fuels contributes significantly to emissions of greenhouse gas, the main contributor to the current global warming. Besides the negative environmental effect of excessive use, energy from fossil fuels can put at risk the future global energy security due to the significant drop in remaining resources on Terra. Burning fossil fuels for energy requirements contributes to the increase in greenhouse-gas concentrations in the atmosphere [17]–[32], thus enhancing the security of power supply chain and diminishing the greenhouse-gas emissions, which require heedful care and serious consideration now more than ever [33], [34]. This is the main reason why both local and global measures need to be taken.

Increasingly countries have taken steps to favor the use of renewable energies aimed at alleviating environmental problems and reduce dependence on fossil fuels. Following these measures, wind power has had a rapid growth after 2000 [35]–[39]. Romania’s energy potential derived from renewable-energy sources consists of: solar energy, wind energy, biomass, hydro and geothermal energy. The largest contributor in this case is represented by hydro energy, followed by wind energy. Hydroelectric power can be stored, and electricity can be produced at a constant rate. These two are the greatest advantages of it hydro energy, but they present many disadvantages too. Among hydroelectric power drawbacks we could mention:

Dams and all hydroelectric power plants are very expensive to build;

Payback period is significantly long;

Natural environment may be destroyed[40]–[44];

Effects on agriculture;

Dependence on annual rainfall levels;

Hydropower is a sustainable and long-lasting source of energy but building a hydroelectric power plant raises many environmental concerns.

Among the ways in which electricity can be generated from renewable-energy sources (RES), the one based on wind turbines is believed to be the least harmful to the environment [45]–[47]. It has also been the most cost effective of the RES, until now [48]. Due to the combination of these two factors, wind energy is the most extensively utilized of all renewable-energy sources for electricity generation if large hydropower is excluded from consideration (as it usually is) [49], [50]. Wind energy is sustainable and long-lasting too, pollution free and eco-friendly [50]–[76]. Wind energy is a clean renewable-energy source [51], [52], [77]–[80] and is strategically important to national and socioeconomic development [81], [82].

This section main objective is to emphasize wind power energy potential in Romania and to analyze and present this sector at its current state. As a European Union member, the first step of our research was to evaluate this type of energy at European level. Having assessed this, based on energy dependency across EU countries – energy from renewable sources across EU countries, we subsequently put emphasis on the wind energy sector. For each criterion we identified and highlighted our country’s position inside the European Community.

We chose to present Romania’s wind energy sector in detail, because it is the second largest segment of renewable energy, in Romania, after hydropower energy. The greatest hydropower plants in Romania were built long before the country’s accession to the European Union. In the last 27 years only maintenance of existing facilities and resumption of older projects have been made in this sector. In contrast, in short periods of time substantial amounts of money have been invested, in wind power plants. This strategy seems to result from climatic changes (global warming) and longer periods of recorded drought, which hinders investments in large hydropower plants but supports other types of renewable-energy sources.

Electricity is important for socio-economic development, and the power consumption is essential to all sectors. In Romania, the electric power industry has seven components: hydro, coal, nuclear, hydrocarbons, wind, photovoltaics and biomass. The most important power plants in Romania are presented in Figure 11, and their share on the 22nd of February 2016 is presented in the bar of the pie chart included in the right upper corner and detailed in Fig. 32.

Fig. 32. The map of electric power industry in Romania, by type and location [83]

Romania’s wind energy sector is currently undergoing dynamic changes, although our first professional wind farm projects were developed only a few years ago. At the end of 2009 Romania had an installed wind capacity of just 14 MW but at the end of 2010 its wind power station capacity amounted to 462 MW. Now this type of energy is beginning to play an increasingly important role in our country and for Southeastern Europe. Romania's potential in wind energy is very high, being considered the highest in South-Eastern Europe and the second in Europe [77].

The foundation for the development of electricity production from renewable sources and especially wind is represented by two prerequisites:

the high potential within the country related to renewable energy and especially the wind;

the significant support received by investors in this sector, through Green Certificates obtained for each MWh supplied.

Although Romania’s wind potential is high, the first investment in wind power was performed in late 2004. This was done in the Ploiesti Industrial Parc by installing a single group with the power of 0.66 MW.

Due to 220 Law coming into effect, the year 2008 is considered to be a milestone for the development of electricity production from renewable sources. Until this year, the main sources of electricity production were the fossil fuels, nuclear power and hydropower, as can be seen in Fig. 33. Hydroelectric energy is the sole source of electricity production from renewable sources and accounts for 33 % of the total electricity produced. The total electricity produced in 2010 in Romania was of 60.7 TWh, out of which 20.33 TWh were produced from renewable sources mainly hydroelectric energy (20.05 TWh) and wind energy (0.27TWh).

Fig. 33. The mix of electric energy in Romania, in 2010 [84]

By 2010, the electricity production from renewable sources developed and increased rapidly so that in 2015 the total energy produced from renewable sources in Romania reached 38.6 %, which means that the electricity produced by the renewable systems was of approximately 24.35 TWh.

The two main sources of the renewable energy which contributed to this value were hydro (16.13 TWh) and wind (6.50 TWh). Although, lately, the sector for photovoltaic and biomass has been significantly increased, it could only deliver 1.72 TWh.

Fig. 34. The mix of electric energy in Romania, on February 22, 2016 [84]

Worldwide, the leading sources of renewable energy used for electricity production are hydro, wind, photovoltaic and biomass.

The RES sector has suffered significant changes because of the associated legislation. The system dynamics concerning the production of electricity between 2000 and 2015 changed mainly due to new producers entering the wind, photovoltaics and biomass sector. They become important players on the Romanian energy production market, being capable of generating significant amounts of electricity, as shown in Fig. 35.

Fig. 35. The growth of RES sector in Romania, between January 2010 and December 2015 [85]

Electricity production from wind sources experienced the most rapid development, due to the high wind potential and supporting policies for renewable-energy production. Wind energy in Romania has developed in a short period of time. In less than five years 75 wind farms with a power range from 0.008 to 600 MW and an average of 40 MW were built. In this period 1,200 wind turbines have been installed on the entire surface of Romania. This development of wind farms was achieved primarily in two regions: the core in Dobrogea Plateau, with near 78% of the total power installed, and a secondary one in Bârlad Plateau. The largest onshore wind farm in Europe is located in Dobrogea, in Fântânele and Cogealac, having an installed power of 600 MW. The wind farms locations throughout Romania are displayed in Fig. 36.

Fig. 36. Wind farms locations throughout Romania at the end of 2015

At the end of 2015 wind farms with an installed power of 2,838 MW were already connected to the national electricity network, with another 100 MW approved for connection [84]. While in 2009 the set up capacity was only 14 MW, in 2010 investments in wind energy intensified, reaching at the end of 2014 an installed power of 2,594 MW. This rapid development of the sector was blocked in 2013 by the change in the Green Certificates granting scheme. After this year, investments in new wind farms have gradually decreased, as shown in Fig. 37.

Fig. 37. Installed wind power and total wind power between 2009 and 2015, in Romania [84]

The wind power sector began to play an important role in national energy policy after 2013. The peak in terms of the electricity provided by the wind system was in December 2014, when 0.82 TWh were produced, accounting for 14.2% of all the energy produced in Romania during that month. The wind-power electricity produced has increased gradually from 2013, reaching a record level for Romania in 2015, as can be seen in Fig. 38.

Fig. 38. Monthly energy provided by the wind system in Romania, between 2010 and 2015 [84]

Today, the only way to develop the electricity sector from wind, or other renewable sources is by subsidizing the electricity produced from these sources or by providing financial support to the developers of such energy sources. The use of renewables, in particular, wind power, so as to produce electricity is a clean and environmentally friendly way, and by all means the producers should be encouraged towards sustainable development in the next period. The progress in the wind power system development helps EU countries to meet the targets set by the Directive 2009/28/EC on the promotion of electricity produced from renewable-energy sources in the internal electricity market.

The present study has addressed several aspects related to present and future development of on-shore wind power in Romania, as a member of the European Union.

Romania was in 2014 on the third place in top EU countries with the lowest energy dependency, after Estonia and Denmark. The share of electricity from renewable sources in gross electricity consumption, for Romania in 2014, was 41.7%, placing it on the 7th place in the European Union.

The wind energy in Romania witnessed considerable development over the five-year period of time, 75 wind farms with a power range from 0.008 to 600 MW and an average of 40 MW were built.

Fig. 39. The core of wind energy in Romania

Over 1,200 wind turbines are spread on the entire surface of Romania. This development of wind farms was achieved primarily in two regions: the core in Dobrogea Plateau with near 78% (see Fig. 39) of the total power installed, and a secondary one in Bârlad Plateau. The largest onshore wind farm in Europe is located in Dobrogea, in Fântânele and Cogealac, having an installed power of 600 MW.

Appliacations of refrigeration and cryogenics in Bioengineering

The history and origins of Cryogenics

The word Cryogenics is a product of the twentieth century and comes from the Greek word κρϋς – frost or γίυομαί – to produce, to endanger. From etymological point of view, the cryogenic word means the science and art to produce cold. This definition may be appropriate today, but definitely was not used in the usual way with this simple to understand, the first recorded use in the late XIX century.

At the beginning of the century XIX, in 1826, the term cryophorus or carrier frost (in French cryophore) it was used by Wollaston to describe a device to illustrate the freezing water by evaporation: the device consists of two glass flasks connected through a tube, one containing water and the other a hygroscopic material.

Later, in 1875, the noun cryogen from English (and cryogène in French) has begun to be used to describe a mixture refrigerant, or ice mixed with a substance that produces a mixture refrigerant (English dictionary Oxford, edition 1989).

The adjective cryogenic (cryogènique), has gained limited use early next century, meaning ‘which or refer to the production and use of low temperatures’. For example, the first recorded use of the word is found in the term Dutch ‘kryogeen laboratorium’, in an article readed by Kamerlingh Onnes to the Dutch Royal Academy of Science, on December 29, 1894.

Normal boiling points of these gases in the liquid form are all under temperature 120 K and this temperature border had become general of very low temperatures, associated machinery, apparatus cryogenic (under 120 K), and low temperatures of engineering (technology) refrigerated (over 120 K).

Technically speaking, border of 120 K is real because very low temperatures -under 120 K-, in general, can be achieved with a refrigerating machine which incorporates expansion of the gas with a regenerative or recuperative, where heat is exchanged between the admission and exhaust streams of working fluid. To obtain temperatures below 120 K, you can choose a working fluid with a critical temperature below ambient, so you no longer need for heat exchangers, although they may be incorporated to improve machine efficiency.

Origins of using the noun ‘cryogenics’ from English language (or cryogènie from French) are more obscure. While the French noun may have been mentioned since 1900, the English version appeared only to 1940, when it was associated with enlarged production and use of liquid helium and liquid hydrogen, following the appearance in USA in 1946, f the liquidator / cryostat of helium / hydrogen from Collins'.

For some, the word eventually became synonymous with cryogenic technology – the art of producing liquid helium, liquid hydrogen and to a certain extent, air components in the liquid form. For others, the word includes both art and science of very low temperatures, and from there, was used to describe the physics of low temperatures. For example, the edition from 1989 of Oxford English Dictionary introduce cryogenics as ‘that branch of physics that deals with the production of very low temperatures and their effects on matter’.

At 120 K, upper temperature boundary begins to disappear, when the prefix ‘cryo’ begins to be used in years ’60, with words such as cryopumping, cryochillers and cryomedicine. Biological and medical uses of the prefix had interference with cryobiology, cryoconservation, cryosurgery, cryosensor, cryogenic freezing (cryofreeze) and so on, but the temperatures were not working now determined by the use of permanent liquefied gas. Instead, the prefix ’cryo’ was correlated to status change of biological material or tissue in which water turns to ice.

1. Domains of temperature. (a) Temperatures below 120 K (approx.) They will be called cryogenic temperatures, or preferably, cryo temperatures. Terms such as low temperatures or ultra deep low will be avoided.

(b) Temperature zones must be indicated by numbers on the scale of temperature, and if you use phrases like LNG or liquid helium temperatures, they will also give numerical indications.

(c) Use of terms milikelvin (mK = 10-3 K) or microkelvin (μK = 10-6 K) is preferred, but not exclusively.

2. Cryogenics, cryogenic, cryo – . (a) From etymological point of view, cryogenic means science and art of cold, and everything has direct connection with it. However, in the last 20 years, it has assimilated a wide variety of meanings, as ‘science of low temperatures or ‘technology of low temperatures’, until a simple qualifier, synonymous with ‘extremely low’ like in ‘cryogenic temperature’. The working group has received requests from various independent associations introducing a comprehensive new term ‘cryology’, wich, in accordance with generally accepted use of language, would cover everything treats or deals with ‘cold’, namely low temperatures, especially those under 120 K. The working group was strongly in favor of introducing the term ‘cryology’ even realize that the general acceptance would take a long time. Derived words such as crylog or cryologyc should also be encouraged.

(b) In the use of words ‘cryogenics’, ‘cryogenic’ and ‘cryo-‘ , all three forms must have the same general meaning, respectively covering all phenomena, processes, techniques or apparatus used or occurring at temperatures under 120 K, and not only establishing and maintaining temperatures under 120 K. Most of the working group expressed hope that the prefix 'cryo' would have preferred the adjective 'cryogenic'.

(c) Although efforts must be made to keep root 'cryo', for the temperature range under 120 K, some inadvertence is inevitable. Is there scientific terms accepted by a long time (e.g. cryohydrate, cryoscope, cryodrying), where ‘cryo’ denotes just a temperature under 0oC. A term recently added is 'cryochemistry'. The working group recognized the fast-growing field of cryosurgery, cryomedicine and cryobiology; the use of 'cryo' is justified by the fact that appropriate tools, techniques and disciplines derived from cryogenic techniques and mostly used cryogenic fluids.

3. Superconductivity. (a) The term temperature Onnes of the transition temperature of a superconducting domain zero should be abandoned.

(b) In scientific terminology, conductivity the term is usually understood as specific conductance value. It would therefore be preferable to use the term superconductor when referring to a phenomenon, and not the superconductivity.

4. Liquid helium. The working group was in favor of retention terms: helium 3, helium 4, He I, he II, helium pellicle, flux of the pellicle (film flow). The term λ-leak [spillage λ] (or lambda) should be used to denote a drain under the unexpected λ, while the superinfiltration / leakage / dispersion (superleak) means an ensemble with a special destination (e.g. fine pores, capillary, canals), superfluid helium permeable.

Three ingredients for a successful technology: interaction triangle

The origins are found in cryogenics research and development work primary from low temperature physics and chemistry, but this is far from the whole story.

Fig. 40. Interaction triangle for the successful development

The recipe for success in cryogenics was born from the collaboration of universities, on the one hand, and innovation for industrial and commercial common sense, on the other hand, along with communication and proper training, to obtain the fruits of the collaboration. The three ingredients, research, industry and training, brought together through the interaction triangle (Fig. 40), appearing wherever there is a thriving technology. On the other hand, there are failures in cryogenics, even after spending large sums of money, success does not occur if one of the three ingredients is missing.

It is difficult to assess today the development of techniques and equipment problems at low temperatures. There is an abundance of data about physical and mechanical properties of solids and insulation materials, and thermodynamic data about fluids are easily accessible. In 1880, there were no data about the solid state, while data were inaccurate and sparse fluids under –78oC, temperature CO2 solid. Critical conditions associated with the phenomena were not understood, thus constituting a barrier to progress towards lower temperatures.

Now we know much more, and the equilibrium diagram P-T from Fig. 41 summarizes how all gases (except helium) behave like the liquefaction and solidification. The critical point corresponds with the pressure and temperature above which there is no difference between the vapor and liquid. Most critical for proper gas pressures are quite low – under 50 atm – and early attempts gas liquefactions by applying very high pressures were superfluous and unnecessarily risky.

After a gas liquefaction (let say SO2) by cooling below the critical temperature under a pressure below the critical pressure, fluid temperature can be further lowered by reducing the vapor pressure above the liquid. This cold liquid can now be used to liquefy a second gas (CO2 or ethylene say) to a high pressure lower than its critical pressure. The temperature of the second liquefied gas can now be lowered by pumping vapor at a lower pressure. In this manner, temperatures increasingly lower, touching in steps, or cascade; however, there is a limit below which we can use alternative cooling technique. It is necessary to expansion of the gas, either through a throttle (expansion the Joule-Thompson) to produce internal cooling, or a reciprocating engine or turbine, to produce cooling by the processing of external work.

Technical cascade with a floor expansion of gas was first used by Pictet in 1877 to liquefy oxygen. It was later used by Dewar in 1898 for liquefying hydrogen, using a cascade of ethylene, hydrogen and air. Variant of the cascading technique is still widely used today for liquefying natural gas, hydrogen and helium.

Although the technique expansion of Joule-Thompson widely used given its simplicity, with no moving parts at low temperatures, to understand very little about the physical details on the process (except that what they published Joule and Thompson in 1852), late in the twentieth century.

Fig. 41. Diagram pressure – temperature of all gases (except helium), illustrating the triple point, the critical point and pressure-temperature curve vapor saturation of the liquid phase

Of course, physical process that involves liquefying air raised controverses major at that time. At least two researchers had the impression that the Joule-Thompson was supplemented by additional cooling effect.

For example, Pictet's ideas have been advanced by a few years, between the 1903 and 1907 ideas that included a formula for the cooling effect on the expansion valve 'by processing the external surface for overcoming the prevailing pressure in front of valve'. Also in 1904 Cottrell, whose liquefaction (built Brins Oxygen Company) has just been installed in Berkeley, California, discussed yield low (7-8%) of this type of air liquefaction and noted that:

While the Joule-Thompson is arguably responsible for the whole process of cooling down the critical temperature of the gas, it is, probably supplemented, if not actually replaced under this point of condensation direct gas in the pressure pipe behind the exhaust valve, the latent heat from this process being taken over by current return of the atmospheric air.

In 1906, Cottrell at Berkeley and Bradley at Wesleyan University, Middleton, Connecticut, have communicated their findings simultaneously. Both authors had amended air flow lichefiators so that high pressure can be cooled in a spiral immersed in the liquid air, before expansion already collected by Joule-Thompson valve. There was no difference observed in the rate of production has liquid air whether or not spiral was covered with liquid air. Bradley continued with a thorough study has flow path length distribution of temperature, high pressure valves until expansion and proves essentially in 1906 as Joule-Thompson effect was alone responsible for liquefying air.

Over the next two decades, there have been measurements of temperature and thermal PVT on a variety of gases, by many groups in Europe and North America. Thermodynamic diagrams could be developed and therefore, there could eventually describe precise understanding of the process Joule-Thompson – for example, see a summary of this work conducted by Lenz in 1929.

After low temperatures were conducted in an enclosure, it is necessary to provide insulation to prevent or reduce heat penetration from the medium of ambient temperature. Table 6 gives indications about heat flow per 1m2 of various insulations with a standard thickness of 2,5 cm. The table shows how the introduction of Dewar (1892), the silversmiths' apparent inner surfaces of a double-walled glass vessel, provided a significant improvement in performance insulation. If he increased the number of reflective layers around the three layers that you used, Dewar would have achieved a significant reduction in heat flux and had discovered the principle of multi-layered insulation. The flasks or double-walled vessels' Dewars for keeping liquefied gas would be used layers of foil (metal) instead of silverware; Dewar vessel and subsequent adaptation for keeping liquids hot items would have led to be quite different from Thermos vessel known today. In fact, multilayer insulation technique was not developed until 1950, when they appeared demands for lighter-weight insulation at cryogenic fuel's tanks for space shuttles [86].

Table 6. Insulation performance

The history and origins of biological material preservation

Conservation of biological materials over long periods of time is a very important issue in the food industry, medical and biotechnology in general. Principle of conservation of biological material is rooted in the observation that life processes are temperature-dependent chemical reactions, the amount of, which is metabolism. Curing time of any biological tissue is directly related to the temperature at which it is kept.

Reducing the temperature reduces the metabolic processes of the biological tissue, as well as in chemical reactions, and thus, its storage time increases. For example, the metabolic activity of an enzyme in a normothermic animals (animals maintain their body temperature constant) can be reduced to 1,5 to 2 times, by lowering the temperature every 10 °C [87].

It is desirable to keep the body in the lowest possible temperature. Theoretically, this should be zero absolute temperature, in which case all the chemical reactions cease, thus prolonging conservation indefinitely. However, there are some restrictions. Since the preservation is carried out in an aqueous solution, freezing the solution temperature should be minimum temperature at which the organ can be stored. Once freezing occurs in the tissue, can produce irreversible damage to the body.

Most works in the field of cryopreservation have been made under atmospheric conditions, simply because life on Earth takes place in an environment of pressure relatively constant (isobaric) about one atmosphere (1 atm = 1.01325 bar). If a substance is cooled at a constant pressure, freezing is expected if the system goes below freezing temperature, corresponding to the process pressure. In the case of pure water at atmospheric pressure, ice formation is expected at a temperature below 0 °C and under -0.57șC in the case of physiological saline. However, these temperatures may vary for different reasons. For example, for ice to form (bundle very small water molecules with structure similar to ice) should comprise a nucleus. These nuclei occur randomly and are temperature dependent. Ice can also increase using impurity, with a critical size of the nucleus, the nucleus artificially [88]. This nucleation is called nucleation heterogeneous.

The pure water can be cooled down to – 40 ° C, in the absence of impurities [89]. This type of freezing called homogeneous freezing. Ideally, the biological material can be stored at very low temperatures, in a state subcooling significantly reducing cell metabolism and preventing freezing while. Unfortunately, the subcooling and the ice nucleation event is a probabilistic, but in reality, the cells' fluids typically freeze at temperatures higher than -5 ° C in an unpredictable way.

As mentioned before, freezing is a probabilistic phenomenon that depends on the temperature and the volume of solution. It has been found that when the cells are frozen at a cell suspension ice formation begins in the extracellular space, where the volume is greater than the volume inside the cells and in the vascular space and the interstitial wherein when the tissue is frozen [90]. The probability that intracellular freezing cells is much lower because the volume is lower. Even if you could produce occasionally intracellular freezing cells will not cause additional ice formation in other cells. Biological materials during freezing mixture of ice and solution into the extracellular space are not in thermodynamic equilibrium with the supercooled water due to differences in the intracellular concentration of the solute inside and outside the cell. Extracellular concentration will be higher than the cells that cause a higher Gibbs free energy and a potential difference intracellular Helmholtz. In order to balance the chemical potential in the extracellular solution, and therefore, reduce the free energy of intracellular water will leave the cell through the cellular membrane permeable to water. Accordingly, intracellular solution will become hypertonic. It was originally proposed by Lovelock [91]. Mazur [92] later incorporated in the comprehensive theory that with the increase of the solution hipertonicității creates intracellular cell damage, although it is not clear what is the mechanism that causes the damage. Some possibilities might be related to chemical denaturation of proteins, enzymes and other molecules, changes in cellular structure, or both. However, it seems that cell damage increases with increased extracellular levels and exposure time, which validates the concept of chemical damage [90], [91], [92], [93].

The current methods of preserving organs preserved from 2 to 6 ° C [9]. Experiments have shown that the temperature of preservation is not the only parameter affecting the survival of cryopreserved cells [92], [93], [94], [95]. In fact, the rate at which cells are brought to cryogenic temperatures, and the cooling rate is probably the most important parameter cryopreservation heat. Parameter rate of cooling is usually given in units of ° C / min. The effect of cooling rates is related to the mass transfer (mainly water transport) across the cell membrane. Due to kinetic limitations, the composition becomes instantly intracellular equal to the composition of the extracellular. The rates of mass transfer across the cell membrane and cell shrinkage are based on the permeability of the cell membrane and extracellular osmolarity of the solution. Since the chemical destruction is a function of the concentration gradient, which is a function of the presence of ice in the extracellular solution, and as mass transfer who causes cellular dehydration is a function of time, it should be anticipated that, if the cells are rapidly cooled to temperatures cryogenic, chemical mechanism of damage during freezing could be eliminated or greatly reduced. It has been found that the increase of the cooling rate during freezing improves cell survival really [92], [93], [94], [95]; however, the experiments showed that the increase in viability (survival of cells) was reversed sharply once the cooling rates above a certain value optimal cell survival decreases rapidly with a further increase cooling rates. When viability is plotted as a function of the cooling rate, the survival curve similar to a reverse U-shaped, with survival increasing progressively with the increase of the cooling rate until it reaches an optimum rate of cooling, and then decreasing with an increase further rate [92], [93], [94], [95].

This behavior is consistent survival in various cell types. However, the values of each so-called "survival curve in the inverted U-shaped" is cell-type specific and the cooling rate optimum may vary even several orders of magnitude from one cell type to another cell type. Reverse cell survival with the sudden cooling rate higher than optimal may be a consequence of intracellular freezing. Experiments were correlated with the formation of sharp decrease in cell survival intracellular ice [89], [90], [92], [93], [95]. Rapid formation has intracellular ice is related to the dynamics of the mass transfer across the cell membrane during freezing.

When cells are cooled too quickly there is enough time to equilibrate intracellular solution in concentrations of extracellular solution. Following intracellular solution is thermodynamically cooled. The probability of intracellular ice nucleation achieves increases with the degree of supercooling thermodynamically. It is not yet clear whether nucleation site is intracellular, extracellular or membrane [96]. However, regardless of the cause, intracellular ice formation is almost always lethal to cells. Therefore, it must be avoided in the design cryopreservation protocols [97].

Preservation in the constant pressure system

The main objective of cryopreservation is to avoid chemical damage due to the freezing of the intracellular product to extracellular levels of high subzero temperature. As discussed above, the techniques of cryopreservation used at present are mostly made during the process of the isobaric (constant pressure), which is held at one atmosphere.

The most obvious method, when working at constant atmospheric pressure to reduce chemical damage at temperatures below zero, is the addition of compounds which depresses the freezing temperature of the solution. It is also necessary that compounds where can penetrate the cell membrane to the cell and not affect its constituents. In addition, it is relevant to this study recognize that most cryoprotectorants agencies need to be able to easily penetrate the cell membrane to be effective; otherwise, the cells may become hypertonic, as explained above.

Early modern criobiologiei can be traced to 1948 in the work of Smith and Parkes Polge, who could preserve sperm cattle on dry ice temperature of -79 ° C by adding glycerol [98]. It was found later that the other polyol compounds such as dimethyl sulfoxide (DMSO), which penetrates cell membrane, frozen to facilitate cell survival. Crioprotectanții such as glycerol, ethylene glycol and DMSO enters the cell and lower the freezing temperature of the solution, presumably by their colligative effect.

They are diluted in intracellular tonicity and decrease during freezing temperatures far below zero. These cryoprotectants are now used routinely in cryopreservation of cells and form the basis for all successful methods of cryopreservation [97].

Preservation in a hyperbaric system

The concept of pressure-freezing was first introduced in 1968 by the European Conference Moor electron microscopy of Rome [99]. This effect wears concept known as Le Chatelier's principle's. The volume of water increases upon freezing, high pressure prevents the water volume expansion when ice is, and thus prevent the crystallization of the water. Conservation of high pressure was applied mainly foodstuffs [100], [101] but the possible applications are promising to preserve bodies.

As explained above, the immediate effect of high pressure on cryopreservation is to suppress the freezing by lowering the temperature, the phase change of the aqueous solution, allowing for the preservation of living matter at low temperature, without freezing.

Pressure effect is equivalent to that of a chemical cryoprotector advantage that instantly affects the intracellular region and reduce the toxicity of chemical cryoprotectants. For example, at 2100 bars pressure cryoprotectant effect is equivalent to about 20% of the glycerol [102]. Cryopreservation hyperbaric also reduce the concentration of the chemical in temperatures below zero degrees Celsius [103]. The goal of cryopreservation is to preserve hyperbaric solution in the liquid phase. Consequently, the absence of extracellular and intracellular ice solution determines the biological material to remain at the initial osmolality of avoiding damage to the chemical. Hyperbaric procedures are often used in food preservation techniques and tissue structure is maintained for criomicroscopie unlike cryopreservation. The goal of cryopreservation hyperbaric in such applications is to maintain the high pressures and lower temperatures well below 0 ° C, followed by a sudden release of pressure causing freezing very quickly leading to a better conservation of the structure of the biological material [100], [101].

Several attempts have been reported on the use of hyperbaric pressures for organ preservation at low temperatures without freezing appear harmful aspects of, for example, liver [104] and the preservation of cells [105]. In general, higher pressures were obtained in studies using mechanical devices. The pressures used in the experiments liver climbed to values of about 70 MPa. It was found that the liver can survive exposure to about 35 MPa, but succumb to pressures higher. Survival was found to be a function of the compression rate and the magnitude of the applied pressure. It has been found in cells, where the pressure independent of temperature has been examined, which were able to survive up to 200 MPa pressure for short periods of time and that ATP (adenosine triphosphate) is exhausted [105]. There are certain mechanisms that can lead to cell damage from hyperbaric cryopreservation protocols described in these studies. The most obvious is the negative effect of very high pressure on cells. However, the traditional cryopreservation hyperbaric there is no attempt to minimize the pressure of cryopreservation for a given temperature. In a cryopreservation system isochoric (constant volume), the system is set at the minimum pressure natural for the particular cryopreservation temperature and pressure thereby reduce toxicity. Another convincing argument in favor of hyperbaric cryopreservation cryopreservation isochoric is based on the fact that in the latter the necessary technology device is cumbersome and expensive, and the technology in the first device is extremely simple and cheap.

In the present paper, the cryopreservation process isochoric is proposed as a new possible method for preserving organic material. The basic idea of this method is to take advantage of the expansion pressure developed in a room isochoric ice to lower the temperature to freeze remaining liquid if it could be preserved organic material. This method has a disadvantage inherent and possible damage that high pressure could cause material preserved [97].

Isochoric freezing method. Process description and device proposal

Isochoric pulsed freezing method is a method of biological materials thermodynamic cooling at or below the temperature of -10 ° C, ensuring that the intracellular and extracellular space to their fine structure of ice crystals. The biological material is introduced at atmospheric pressure and temperature in a room isochoric (1). Isochoric interior volume of the chamber is filled with an aqueous solution of biologically compatible material so as to ensure total removal of gas between the cover (2) and the surface of the aqueous solution. The lid (2) is provided with a valve (3) communicating with the external environment. A part of the isochoric chamber (1) is provided with ice crystallization promoters. Isochoric heat extracted from the room by means of the cooling system (4). After the appropriate pressure to achieve the temperature of initial freezing, air, as the room temperature falls isochoric and ice crystals appear in the promoters of the crystallisation of the chamber isochoric pressure in the volume isochoric increase, the relationship between temperature and pressure in the chamber isochoric seeking equilibrium curve of liquid and solid phases of. When the temperature appropriate negative pressure balance of the prescribed phases of the water in the biological material will be subjected to isochoric cooling liquid and the product to be frozen. By opening the valve (3) communicating with the exterior, virtually instantaneous drop in pressure in the cylinder isochoric creates a thermodynamic state of imbalance. Reaching the state of thermodynamic equilibrium is achieved by high speed crystallization, all biological material volume. In the process described, the biological material is presented in a frozen state with an intracellular structure consisting of fine ice crystals. This process can be repeated until all biological material is frozen.

This device relates to a thermodynamic isochoric freezing method and to an apparatus in order to achieve pulsed isochoric freezing process.

Progress in technologies for food storage enable the feeding of the world population.

Cooling has been used for centuries to preserve food and avoiding its degradation. Reducing the temperature has the effect of slowing down the chemical reactions of the process tipmetabolism components. This is why keeping food at low temperatures lead to reduced greenhouse destructive dynamics of chemical reactions and also an inhibitory role in the development of pathogenic micro-organisms and other elements.

Viewed from this perspective, at least in theory, lowering the temperature would have a beneficial effect on food storage. However, biological materials are composed mostly of water and the temperature drops below the freezing point of water produce important changes in physical constitution of food. The crystals of the ice formed in the extracellular space both affect the texture of food as well as extracellular decongelatcu negative repercussions on the process of preservation.

Cooling the food product is a process in which heat is transferred from the outer surface of the product to a cooling medium.

In conventional freezing processes, the initiation process begins at the outer surface of the product, which is in contact with the cooling medium, and propagates inwards ice crystallization.

Fig. 42 is a schematic view of the propagation of the front of the freezing in a plate to cool on the outside with an environment at a temperature below the freezing point.

Fig. 42. Scheme of the propagation process from freezing outside of the front plate in an object. The temperature of the cooling medium is T0. The temperature of phase change is Tph and s(t) the surface of the phase change is propagated in time, from the outer surface of the product inside. Frost is performed when To(K) < Tph(K)

The freezing of biological substances happens after a complex process of heat and mass exchange. To preserve biological structure of matter, the process of freezing, that goes also extracellular must occur at a certain cooling rate [106]. Microscopically, in the case of solutions, the freezing process is going on in the form of microcrystals, as illustrated in Fig. 43. The mechanism is well described in the theory of nucleation of ice and constitutional instability [107].

Fig. 43. Crystals in the form of fingers which are formed during solidification dimensional saline.

In general, the rapid freezing at high speed we obtain ice crystals of reduced size. The smaller ice crystals are, much better kept from morphology and biological materials to better the quality of food preserved by cold [108]. The importance of rapid freezing for food preservation was first noted by Clarence Birdseye American inventor who asked, in 1929, the foundations for a quick freeze food storage [109].

Quick freezing procedure is known commercially as the cryogenic freezing or by dipping. It is a process by which food is frozen quickly at cryogenic temperatures. Frost speed directly affects the nucleation process and the size of the ice crystals. In cryogenic freezing of food is quickly immersed in a cryogenic agent, such as nitrogen at -196oC or a mixture of dry ice (solid CO2) and ethanol [110]. Industrial-scale process is performed in large freezers at temperatures well below freezing. Ideally, food should be frozen as soon as they were processed and pending trial is only a few hours. After the cryogenic freezing, foods can be moved in a conventional freezer, where the biological product to be keep solid in an environment whose temperatures are close to freezing point. If cryogenic freezing food quality is high, the process is expensive because it requires equipment operating at extremely low temperatures.

In freezing systems, category falls much cheaper facilities of 'mechanical freezing". Mechanical freezers were, in fact, the first systems used in the food industry and are used in most freezers and cooling chains. They operate on the basis of a conventional cycle with mechanical vapor compression. The refrigerant, at a temperature below the freezing temperature of the product, extracts heat from the product subject to freezing, directly or through a carrier of cold in a heat exchanger acting as evaporator. This heat is transferred to a higher temperature level of the ambient temperature and transferred to the environment. The cycle is resumed by bringing the temperature of the refrigerant which is close to that of the environment, to the temperature of evaporation. Conventional freezers, mechanical vapor compression operates at lower temperatures but close to freezing. Although are cheaper than cryogenic systems, they have the disadvantage that cannot achieve mass biological product subject to conservation by cold, a structure characterized by small ice crystals.

Although the cryogenic freezing, rapid cooling achieved and crystals of small dimensions, there is naturally a weakness in terms of the final result of the freezing process. As shown in Fig. 44, the freezing of the food is performed from the outside to the inside. Regardless of the used cooling medium, liquid nitrogen or very low temperature gas, the freezing process is propagated to the outer surface, in contact with the cooling medium to the inside (Fig. 44). Because of this freezing process is dependent upon the heat capacity of the product under freezing. Due to this fact cannot be formed in the whole bulk of the product uniformly small crystals of ice.

In the case of cryogenic cooling, ice crystals will be small close to the outer surface area, increasing in size towards the inside.

The device covered by this section discloses a method and a device for freezing biological materials that can perform small crystals of ice in the treatment cohort, across the table, regardless of the area of contact with the coolant. Consider the principle used an innovative combination of concepts from freezing and freezing droplets isochoric.

A common method of cryopreservation (frozen storage) cells, is rapid cooling to temperatures below the freezing microdrip containing these cells [106].

The likelihood of ice nucleation particles is a function of temperature and volume. In small volumes of water and the solutions can occur subcooling, that are liquid at temperatures lower than the phase-change temperature [111]. As soon as the ice began forming crystals in a subcooled fluid, thermal energy extraction speed is very fast, and the ice crystals are extremely small. This rapid freezing technique is used to achieve cryopreservation of cells in microscopic volumes. This method can only be used for very fine droplets of clear solution in which the probability of random nucleation is small, and the solution may become subcooled from the thermodynamic point of view. However, it should be kept in mind that in the particular case of food, large volumes of aqueous solutions cannot be subcooling due to numerous heterogeneous nucleation points.

By the present application is proposed a method which can achieve a state of thermodynamic subcooling in a large amount of biological substance with process control in real time, using a new concept namely freezing pulsating isochoric.

An isochoric is a thermodynamic system at constant volume. The concept of freezing isochoric has been described throughout the literature [112], [113], [114]. The principle is based on the thermodynamic equilibrium phase diagram for water (Fig. 44).

Fig. 44. The thermodynamic equilibrium phase diagram for water. The area of interest is the equilibrium line between the ice type I and liquid water.

Figure 3 shows that water, and ice is in thermodynamic equilibrium along the saturation line I which extends at a pressure of 0.1 MPa to about 200 MPa. The triple point of ice I, III ice and liquid water is from about -22șC and 200 MPa. This diagram sugests that in an isochoric system that involves rigidity on its borders, as ice crystals whose volume is higher (lower density) than the water were formed, increases the pressure throughout the system and achieved thermodynamic phase equilibrium between water and ice along the saturation line shown in Figure 3.

Fig. 45 shows the percentage distribution of ice and water in such a system based on the temperature [112].

a)

b)

Fig. 45. Isochoric system. The percentage of the ice depending on the temperature:

a) physiological saline solution;

b) physiological saline solution with 1 and 2 molar of glycerol

The results of the analysis presented in Fig. 45 suggests a model for keeping biological products not frozen state at temperatures below the freezing temperature that correspond to the atmospheric pressure. The isochoric preservation system is shown in Fig. 46.

Fig. 46. Isochoric preservation without freezing. The biological material is placed in isochoric system. Nucleation system is initiated. As the temperature is reduced, increasing the amount of ice in the chamber results in increasing the isochoric pressure. Volume of the tank is calculated such that biological matter to remain ice-free zone, in unfrozen condition, in thermodynamic equilibrium with the ice up to the triple point temperature of ice I, ice III and liquid

Figure 5 illustrates the operation of the concept of isochoric preservation. In the first phase, the biological material is placed inside the isochoric system. Further nucleation system is initiated. As the container is cooled, with decreasing temperature, ice occurrence increases the pressure in the isochoric chamber. The percentage of ice formed at a temperature of about -22oC (Fig. 45) requires that the biological material to be cooled only to fill half of the volume of the isochoric chamber. In these circumstances, biological material remains unfrozen, being in thermodynamic equilibrium with ice at temperatures as low as -22oC. This temperature is sufficiently low to prevent the growth of microorganisms during long-term storage action.

The added benefit of this procedure is that the biological material is subjected to preserve in a not frozen state. On the other hand, isochoric preservation presents a disadvantage from terms of transport; the weight of the device used to achieve proper preservation technique in isochoric systems is very high. If it is possible, it’s easyer to construct such a device where the food is processed. It is not a solution, and it is not economical to transport processed food to the isochoric.

To overcome this obstacle, I describe the concept and technology of pulsating isochoric freezing. Figure 6 shows the thermodynamic cycle of the pulse isochoric freezing.

Fig. 47. Thermodynamic cycle of freezing pulsating isochoric. Point 1, the start of the cycle, is typically at ambient pressure and temperature. The cycle starts with a 1-2 isochoric along the line of phase equilibrium between liquid and ice (and other routes are possible but isochoric process is most effective from terms of energy). The cycle continues with an isothermal process between states 2 and 3 and closes with an isobaric transformation 3-1.

Fig. 47 shows the thermodynamic pulse isochoric process. The cycle begins in state 1 usually characterized by atmospheric temperature and pressure. The first cycle process is conducted between states 1 and 2. The process is characterized by isochoric heat extraction system. The process is the balance line of the ice-liquid phases. No interaction through exchange of work between the system and its surroundings; Energy exchange is characterized only by transfer of heat to the outside. In state 2 system is put into contact with the external environment virtually instantaneous low pressure. Technically, this can be achieved by opening a valve which connects the isochoric chamber to the environment. 2-3 is the lamination process, virtually instantaneous, is keeping practically unchanged the liquid temperature in the isochoric system. Leakage of liquid from the chamber isochoric can be considered insignificant.

In stage 3, the system is in a state of thermodynamic disequilibrium; subcooled liquid is below freezing temperature of -22șC and at the pressure of 0,1 MPa (this steady state at this temperature and pressure corresponds to that of subcooled ice). For this reason, the nucleation begins, the droplets of water in the subcooled state is converted into small ice crystals. The process of forming small ice crystals evenly by the entire volume and is carried out at the atmospheric pressure finally reaching the thermodynamic equilibrium state. In state 3 nucleation process occurs rapidly. The 3-1 transformation is a process of closing the cycle achieved by increasing the temperature at a constant pressure by heat input from internal nucleation points for subcooled environment. Subcooled solution absorbs latent heat released by the freezing process initiated at the point of nucleation, heterogeneous distributed in volume and at different temperatures. As the frost releases latent heat of subcooling temperature of the solution increases, and the crystallization process proceeds to higher temperatures, uniformly throughout the volume of the subcooled. It occurs formation of small crystals of ice volume evenly spread subcooling process observed for rapid freezing microdrip undercooling [107], [106]. The process is independent on the size of the volume of preservation. The transformation described is the cornerstone of the pulsed isochoric freezing cycle.

Cyclical freezing process can be resumed pending complete freezing. Another option is to achieve fine crystallization of intracellular and extracellular space of biological material based on a single pulse isochoric and continuing the freezing process in a conventional system by removing heat from the surface of the product.

Analyzing the cycle as a whole, it is noted that the system does not change mechanical work with the exterior. Exchange of work with the exterior will feature expanded system consisting of system isochoric pulsating freezing and isochoric cooling system cylinder. Isochoric pulsating freezing process is characterized mainly by transferring heat to the outside between states 1 and 2. From state 2 by opening the system to the environment, the terms of preservation at low temperatures for intracellular nucleation of the product are achieved. Fig. 48 shows schematically the device.

Fig. 48. Device for freezing pulsating isobaric

Fig. 48 shows the scheme of the device for pulsing isochoric freezing. The device is a constant volume tank (Fig. 49) designed to withstand the stresses of isochoric process. Isochoric volume capacity (Fig. 49) can be separated into two parts, the lower part is formed by nucleation of ice and the upper support substance containing biological material subjected to preservation. The separation between the two spaces allows potential equalization Helmholtz achieving thermodynamic equilibrium in the solution from two rooms, inhibiting ice nucleation but in the upper chamber. This can be achieved if the septum is used as a porous medium. The chamber is provided with a valve which allows instant pressure equalization with the ambient room. It may be a simple solenoid operated open/closed valve.

Control elements for the variation in temperature can be positioned on the wall of the room or on the outer surface of the wall.

The temperature control system for the ischoric chamber can be uniformly distributed or may be placed several individual systems to follow the progress of temperature on different isochoric areas. The system can be provided with safety valve or pressure valve to monitor the pressure.

In a routine process, the biological material is introduced at the top of the isochoric chamber (filled with carrier solution) at atmospheric pressure and at a temperature above the freezing temperature. The chamber is closed, and the system is cooled under isochoric. At the desired temperature/pressure, the chamber is opened to a lower pressure, preferably atmospheric pressure. Biological material ice nucleation occurs. The cyclic process could continue or biological content could be cooled at an atmospheric pressure to other temperatures, cryogenic even with the advantage that the biological material is currently evenly ice cores distributed in whole volume. For storage, the biological material is removed from the isochoric chamber and stored at the desired temperature, for example -10oC. Likewise, is the case of rapid freezing by immersion in a cryogenic liquid; In the latter case cooled by dipping the biological material is stored at a conventional temperature of about -10°C. In relation to freezing by immersion, where freezing temperatures isochoric pulsating required are submitted but the cold and cryogenic nucleation of ice crystals are evenly distributed throughout the volume of biological material under freezing (Fig. 49).

Fig. 49. Isochoric cylinder provided with valve connection with environment for conducting the thermodynamic cycle of freezing pulsating isochoric

Isochoric cooling system can be designed in various configurations depending on the purpose. In Fig. 50 is presented a prototype version for industrial or in Fig. 51 a version for laboratory experiments.

Fig. 50. Device for freezing pulsating isobaric cooling system for industrial prototype version

Isochoric tank (a) is introduced into an outer tank (b) filled with a solution of cold accumulation (c), which may be a water-glycol solution. Outer vessel is well insulated from the environment. The space between the two tanks (a) and (b) in the cold accumulation solution the evaporator (d) of a refrigeration system is mounted. The space between the two tanks is provided with an agitator (e). Isochoric cooling cylinder speed will be controlled by varying the stirrer speed and by varying the temperature of the refrigerant vapor with an adjustable electronic expansion valve (f).

Variant 2 (Fig. 51).

Fig. 51. Proposed pulsed isochoric freezing cooling system for laboratory

The outer vessel (D) in which the isochoric chamber (A) is palced, is filled with a solution of cold accumulation (K) with a minimum freezing temperature less than the temperature of cooling of the biological product, below -22șC. In the cold accumulation, solution is immersed the shaker (E). The agitator is provided with blades (F) having a removable inner space filled with the solution freezing point (thaw) equal to the minimum cooling temperature of the biological product (G). Finally, the solution where is immersed in the isochoric chamber has a temperature lower than the minimum cooling temperature of the biological product (under -22șC) and the agitator blades have inside the solution in ice state. The balance will be considered when the system reach minimal cooling temperature for the biological product (below -22șC) and the solution (ice) from agitator blades is on the minimal temperature of the biological product and begins to thaw. During the time when complete solution thawing occurs for cold accumulator solution located in the agitator blades vessel surface temperatures remain constant and equal to the minimum temperature of cooling the biological product. Isochoric cooling rate of the vessel can be adjusted from the speed of rotation of the impeller and the solution cold accumulator chamber which is immersed in the isochoric. Cold accumulation solution can be kept in a Dewar vessel at the minimum cooling temperature of biological product (-22șC), for completion.

Sizing the hyperbaric container and strength verification

To freeze matter in an isochoric system the main component needed is a container with a constant volume. As presented before the problem in isochoric systems is related to high pressures that occur inside these containers, which can be 100 MPa or even higher than 200 MPa. These parameters represent imputs in designing a proper container for the isochoric system. To go ahead with the theoretical study of the isochoric system in this section of my thesis, I describe the designing steps of two containers proposed for further tests. The containers are thought to be made of steel, to have a cylindrical shape and differ by the inner diameter. The two chosen diameters are 32 mm and 65 mm.

Sizing the isochoric container with the inner diameter of 32 mm

Design data

Recipient (container) has the following dimensions:

The inner diameter Di = 32 mm;

Useful volume Vutil = 110,6.103 mm3;

It follows a useful height H=137,6 mm; It will be considered a useful height Hutil = 140 mm. Depending on the design of the sealing system, the total height will be approximately 220 – 240 mm.

Working conditions imposed:

Maximum internal pressure: 275 MPa;

Minimum temperature: -24 oC

The choice of which are made of steel container

The relationship which choose steel from where the cylinders are made of container:

(1)

Where:

σa,c,20o – stress allowable compressive test at a temperature of 20oC;

σa,i,-24o – stress allowable tension test at a temperature of -24oC;

Ri – the inner radius of the vessel;

Re – the outer radius of the vessel;

r – current range;

pi, c – internal pressure of calculation;

σc – flow stress;

With the conditions: r=Ri, pe =0, σa,c,20o ≈ σa,i,-24o ≈ σa, pi,c = 1,1 . pi, min,

it requires calculating an internal pressure greater than that required by the design data fields tolerance because the game will run the cylinders will lead to a range of allowable internal pressure.

The relationship becomes:

pi,c ≈ σa

With these conditions it chooses steel S460NL (W1.8903), SR EN 10025-3:2004, wich at a temperature of -24 ° C has an appropriate resilience.

The specific values that will be used in the sizing calculations are:

pi,c max = 302,5 MPa;

σa = 307,0 MPa.

These values will be used in the calculation of the tensions that arise due to requests thermo-baric.

ReH = 460 MPa;

Rm = 570 ÷ 720 MPa.

The yield strength of the steel at a temperature of -24oC is higher than the temperature of 20°C, but in the absence of specific data for negative temperatures they will use the values described above. Using negative values lower temperatures, ie the application of internal pressure, will increase the safety factor at maximum load.

Pre sizing with minimum external dimensions

Sizing with minimum external dimensions is aimed at determining the number of dimensions of the cylinders and leading to its support an internal pressure of 302,5 MPa calculation. The condition imposed limit is reached, requested material allowable pressure and temperature conditions imposed by design.

Container supports external dimensions’ minimum internal pressure at service for nominal dimensions of cylinders, as derived from the relationships used to sizing. In fact, the manufacture of the cylinder leads to considerable dimensions of the cylinders, in particular the inner diameter, outer, respectively, within a tolerance field, a size field that is imposed by mechanical processing technology used.

The use of cylinder sizes included in the field of tolerance, can have two effects: damage to the inner pressure container or damage to the cylindrical container in the operation tensioners.

Pre sizing with minimum external dimensions

The state of stress in the thick wall

Equivalent stress, according to criterion Tresca:

(2)

Maximum stress is found on the inner surface and is obtained by processing:

Relation (2)

(3)

where:

σt is tangential tension;

σr is the radial tension;

σech is the equivalent stress;

Ri, Re is the inner radius, respectively thick wall outer cylinder;

pi, pe is the pressure on the inner surfaces, outer respectively;

If the number n of rings from where the container is made, the relationship (3) we can write for each cylinder individually, so:

(4)

(5)

……………..

(6)

where:

n is the total number of cylinders

0 is the index for the inner surface of the container

By adding relations (4,5…6) is obtained

(7)

where kn is the ratio between Rn and Rn-1;

because there is no pressure on the inside of the container, equation (4) becomes:

(8)

Identify the minimum number of cylinders

The minimum number of cylinders assembled by tightening, able to sustain the desired pressure, of 302,5 MPa, at temperature of -24oC, is determined by the following conditions:

The thickness of the first cylinder will be at least 15 mm, because the contents of the container sealing gaskets are made via preloaded by threading assembly;

is required k1=2;

Calculating verification will determine whether concentrator tension bolted joint product does not lead to additional tensions; if an overload due to the concentrator will resize properly the first cylinder; request condition consists in reaching the limit of the flow on the inner surface of each cylinder when the pressure reaches the maximum value at the appropriate temperature;

Equation (8) is solved under the conditions given and acquire the data in the table below.

Table 7. Container pressures incurred depending the K report for all cylinders except cylinder 1 and the number of cylinders

where:

Dext is the outer diameter of the container (the outer diameter of the last roller assembly). The values of the ratio of the diameters of the container depending ki for all cylinders, except the cylinder 1 for k = 2,0, as required, are shown in Table 7.

.

Determining the size of cylinders

From the expressions (8) which were determined dimensions of the container, the dimensions shown in Table 1, that the first cylinder has a ratio of outer diameter to the inner of 2,0 and cylinders no.2 and no.3 have a ratio of outer to inner diameter of 1.55. With these conditions, the cylinders have dimensions shown in Table 8.

Table 8. The dimensions of cylinders

Note: dimensions (a are not the final dimensions. They will be corrected by the amount of interference (seraj) of the rings, such that by assembling the pretension to produce desired state of pretension.

Determination of the pressure between cylinders

Using equations (3), all data obtained in 3.b) results in the following interface pressure, pressures shown in Table 9.

Table 9. The interface pressures between the cylinders

Observations

the container made of two cylinders can not bear the conditions imposed termobarice;

has not been taken into account axial tension caused by closures of the container since it has been used the resistance Tresca, which use only maximum stress and minimum,

Intermediate stress (axial) having an intermediate value; A complete analysis of the state of tension is presented in the chapter on the state of stress analysis by finite element method.

the container can be made of a number of three cylinders; in this composition the container will have a minimal outer diameter of 164 mm;

the container will be provided with an additional cylinder, with protection role, where will have the task to mitigate the effects of damage to the outer cylinder; This cylinder protection will be made of the same material, will be weak requested pretension (max. 0,5 from crech) and shall have a maximum thickness. 5-7% of the minimum diameter of the exterior of the container; depending final design of the facility this size to be specified; in this case the container will have an outer diameter of 172-182 mm.

final dimensions of the container will be obtained after the calculation for determining the interference (serajelor)

relations (4 – 6) leading to dimensioning the container to support the working pressure, the pre-tensioning of cylinders from the molded container. But these relationships do not provide equivalent stress and producing less than the limits imposed by the tensioning cylinder assembly. It is necessary to check this situation and if they exceeded the equivalent stress is needed to resize interference (serajelor) between cylinders.

Determining diameter of cylinders wich it is made of the container with minimum dimensions

The overlap effects

The state of stresses that exist in the container is composed of a series of prompts that have overlapping effects.

In Table 10 the pressures acting on each cylinder surface it is made of the container, at each stage of the technological process for the production of container and service.

Table 10. Pressure of the cylinders in various stages of assembly/use

Note: not taken into account in predimensioning nor will take either the verification request produced by cylinder protection because it has a negligible effect on the state of stress in the container, its role is solely to stop the effects after a deterioration (breaking / accidental breakage) cylinders it is made of container.

The total pressure that occurs at the interface between each of the cylinders of the container

From relations (4,5,6) follows:

– for the cylinder no.3:

(9)

because p3=0, then:

p2 = 94,09 MPa

for the cylinder no.2

(10)

because p2 = 94,06 MPa, then p1= 187,15 MPa.

Separate action of internal pressure over cylinders 1+2+3

(11)

at the interface between the cylinder 1 and cylinder 2:

(12)

Pretension cylinders no. 1+2 with cylinder no.3

The pressure of friction between cylinders no. 1+2 with cylinder no. 3 was calculated, as can be seen in Table 11.

The assembly of cylinders 1+2 is subjected to internal pressure, pf12,3.

p12,3 is calculated by the relationship:

(13)

so:

p12,3 = – σr, R1 = 62,51 MPa

Table 11. Values determined for the pressures of the cylinders in various stages of assembly/use

Note: All pressure values are calculated in MPa.

Determination of the equivalent tension at the inside of the cylinder 1 after completing assembly of the container

After completion of the pretensioner at the inside of cylinder 1 is produced the equivalent tension wich is calculated with:

(14)

Between cylinders no. 1 and no. 2 was calculated that there is a pressure pf1,2= p1- po, R1- p12,3=53 MPa, produced assembled by the two cylinders.

elasticity module: 2.105 MPa;

Poisson coefficient: 0,30

These values are the same for all cylinders and temperature values are 24 ° C, the temperature at which the container is assembled.

radial deformation of the cylinder no. 1 is calculated at the the outer surface:

(15)

Cylinder no. 1 is not required on the internal surface.

radial deformation of the cylinder no. 2, is calculated at the the inner surface:

(16)

radial interference is:

(17)

diametral interference is::

radial deformation of the cylinder no. 2 the external surface is calculated:

(18)

where:

ui, Rj – is the deformation of the cylinder i calculated for surface of the radius j

v – is the Poisson coefficient

E – is elasticity module at a temperature of calculation

Determination of interference (serajului) between cylinders 1+2 and 3

– radial deformation of cylinders no. 1+2, calculated at the the outer surface:

(19)

The composed cylinder consisting of cylinders no. 1+2 It is not required on the internal surface.

radial deformation of the cylinder no. 3, at the inner surface is calculated:

(20)

radial interference is:

(21)

diametral interference is:

(22)

where:

ui, Rj – is the deformation of the cylinder i calculated for surface of the radius j

v – is the Poisson coefficient

E – is elasticity module at a temperature of calculation

Determining size of cylinders

4.1. Cylinder 1

D1, int = 32,0 mm

D1, ext = 64,0 + δd,1,2 = 64,07 mm

4.2. Cylinder 2

D2,int = 64 mm

D2,ext = 102,4 mm – 2.u2, R2 + δd,12,3 = 102,4964 mm

4.3. Cylinder 3

D3, int = 102,4 mm

D3, ext = 153,8 mm

where u2,R2, δd,1,2 and δd,12,3 have the values calculated above.

Checking sizing recipient

Checking the equivalent tensions

Checking the equivalent tensions that occur during assembly operations and at the request the internal pressure calculation, calculate relations of Lame and Tresca criterion.

Values are shown in Fig. 52.

Fig. 52. Tensions equivalent produced during assembly operations and at the request of the internal pressure calculation

Checking tension by finite element method

The theoretical component geometry differs from the geometry of the cylinder thick wall of Lame used in relations. There is also an axial load and stress concentrations produced by sealing the container. Checking relationships and sizing was performed by finite element method.

Checking tensions produced in the prestressed components of the container

In Fig. 53 and Fig. 54 are shown tensioned component of the container mesh and the equivalent stress calculated using Tresca criterion.

Fig. 53. Prestressed components mesh

Fig. 54. Equivalent stress calculated using Tresca criterion

Checking tension tensioned container products into components subjected to internal pressure

In Fig. 55, Fig. 56 and Fig. 57 are presented mesh container components and state of tension equivalent calculated using Tresca criterion.

Fig. 55. Prestressed components with internal pressure mesh

Fig. 56. Stress intensity

Fig. 57. Stress intensity in the contact area between container and cap

Sizing the isochoric container with the inner diameter of 65 mm

Design data

Recipient (the container) has the following dimensions:

Inner diameter Di = 65 mm;

Useful volume Vutil = 464,55.103 mm3;

Results a useful height H=140 mm; It will be considered a useful height Hutil = 140 mm. Depending on the design of the sealing system, the total height will be approximately 300 – 340 mm.

Working conditions imposed:

Maximum internal pressure: 275 MPa;

Minimum temperature: -24 oC

The choice of which steel will be used to produce the cylinders for recipient

For this container the material used in calculations is the same as in case of 32 mm container.

Pre sizing the cylinders for recipient

Using the procedures detailed for the 32 mm container is obtained:

The cylinder dimensions it is made of the container are presented in Table 6.

Table 12. The dimensions of the cylinders

Note: dimensions (a are not the final dimensions. They will be corrected by the amount of interference (serajului) between rings such that by assembling the pretensioner to produce desired state of pretensioner.

Through the procedure outlined in case of 32 mm container of the container pressures are obtained in various stages of assembly / use.

Table 13. Values determined for the pressures of the cylinders in various stages of assembly / use

Note: All pressure values are calculated in MPa.

Determining size of cylinders

Cylinder 1

D1, int = 65,0 mm

D1, ext = 130,0 + δd,1,2 = 130,142 mm

Cylinder 2

D2,int = 130 mm

D2,ext = 208 mm – 2.u2, R2 + δd,12,3 = 208,196 mm

Cylinder 3

D3, int = 208,0 mm

D3, ext = 333,0 mm

where u2,R2, δd,1,2 și δd,12,3 have the values calculated above.

Checking sizing recipient

Checking the stress equivalent after the assembly operation

Checking dimensioning container elements was done according to the procedures listed in case of the 32 mm container. Finite element meshing and equivalent stress values are shown in Fig. 58 and Fig. 59.

Fig. 58. Finite element meshing in case of 65 mm container

Fig. 59. Equivalent stress intensity in case of 65 mm container

Checking the equivalent stress, with the container fully assembled and at the design pressure.

Finite element meshing and equivalent stress values are shown in Fig. 60, Fig. 61 and Fig. 62.

Fig. 60. Finite element meshing with internal pressure for the 65 mm container

Fig. 61. Stress intensity in case of 65 mm container closed

Fig. 62. Stress intensity in case of 65 mm container without the cap

Preliminary results with the ischoric preservation system [115]

This section of this thesis is the first experimental evidence showing that a living multicellular organism, the nematode Caenorhabditis elegans, can survive subfreezing temperatures in an isochoric (constant volume) thermodynamic system, while immersed in a simple isotonic solution, without the addition of cryoprotectants. Some of the test conditions were more extreme than those found at the ice/water interface of the Antarctic subglacial Vostok lake. On earth, life takes place in an isobaric (constant pressure) environment. In isobaric systems, subfreezing temperature survival of organisms in nature and subfreezing temperature preservation of living material for biotechnology and medicine, is made possible by use of cryoprotective chemicals additives. Our theoretical thermodynamic studies suggested that in an isochoric system, living biological material could survive subfreezing temperatures, without any cryoprotective chemicals. By confirming the theoretical predictions, this paper suggests a new technology for subfreezing preservation of cells, organs and organisms of possible value for biotechnology and medicine as well as new possible mechanisms of living organism survival in nature [95]. The theoretical results are shown in Figure 1, the left hand side panel. We have also found that only a small fraction of the aqueous solution freezes to the triple point. The right hand side panel of Figure 1, was derived from principles of thermodynamic equilibrium in an isochoric system with pure water [95]. It shows the percentage volume of ice in an isochoric system of pure water as a function of temperature. It is evident that at the triple point 43% of the volume is still unfrozen. In contrast, ice would occupy the entire volume at – 0.001 in an isobaric system at one atmosphere. Fig. 63, suggest that if biological materials are subjected to isochoric freezing temperature they will experience very low hyperosmotic concentrations, without the need for addition of colligative cryoprotectants. Furthermore, if kept in the unfrozen volume, they will not experience any ice. The results in Fig. 63 is the basis for our hypothesis that biological materials could survive subfreezing temperatures in isochoric systems. Obviously, if this hypothesis is verified it may have important implications to cell, organs and organisms’ preservation.

Fig. 63. Left panel. The increase in NaCl molality from an initial isotonic concentration, as a function of temperature, comparison between an isochoric and an isobaric system (Modified from [95]). Right panel. Relation between percentage volume of ice (IP%) and the phase transition temperature in an isochoric system of pure water, as a function of subfreezing temperature (Modified from [95]). (Insert – Temperature versus Pressure thermodynamic equilibrium phase diagram.)

Materials and methods

Caenorhabditis elegans.

C. elegans worms were of the N2 wildtype strain and were obtained from the Caenorhabditis Genetic Center. Worms of mixed developmental stage were grown on standard nematode growth medium (NGM) plates with lawns of E. coli bacteria (strain OP50) serving as food.

Experimental System.

The experimental system is comprised of the instrumented isochoric chamber, a cooling bath, and the cryogenic vial with the nematodes. The isochoric chamber is described in greater detail in [98]. Photographs of the chamber components are shown in Figure 2 (left panel). Briefly, it is based on a pressure vessel, (O-ring 316 SS, inner volume 100 ml, maximal pressure 241.3 MPa) custom designed by Parker Autoclave Engineers (Erie, PA, USA). The pressure inside the isochoric chamber is measured with an Ashcroft 4-20 mA Loop-Powered 20,000 psi Pressure gauge, connected through a NI myDAQ Connector (National Instruments) to a laptop and the data recorded and displayed with LabVIEW. A schematic of the isochoric system and experiment is shown in the top right hand side panel of Fig. 64.

Fig. 64. Experimental system. Left panel, isochoric apparatus. Top right panel – schematic of the isochoric preservation system. Bottom right panel – the cryogenic vial with the pin making a hole.

The isochoric chamber is cooled in a cooling bath. We used two methods. Rapid cooling was achieved with a Nestlab RT-140 cooling system. Slow cooling was achieved by placing the isochoric cylinder in a slush of ice, water and salt in a composition. designed to generate the desired temperature. We used a standard 12 mm inner diameter, 1.8 ml, Fisher Scientific cryogenic vial, capped and self-standing, as shown in Fig. 64 (bottom right hand side panel).

Experimental procedure

The samples were introduced in a cryogenic vial filled with an isotonic solution in such a way as to ensure that there was no air in the vial. The isochoric chamber was also filled with an isotonic solution. An ice nucleating surface was dropped to the bottom of the isochoric chamber to ensure that ice formation starts at the bottom of the chamber at a distance from the vials, which were on the top of the chamber. A small, 0.5 mm, hole was made in the wall of the chamber with the tip of a needle, (Fig. 64) to ensure thermodynamic equilibrium between the interior of the vial and the interior of the isochoric chamber. Three vials were used in each experiment. The chamber was sealed, with care to avoid the entrapment of air bubbles. The schematic in Figure 2 (top right panel) illustrates the configuration in the isochoric chamber. The chamber was immersed in the cooling bath. The pressure was recorded and displayed in real time, using LabVIEW. We had no control over the cooling rate, except through the setting of the temperatures on the Nestlab device or in the slush solution. The experiment was terminated when the desired pressure was reached. The isochoric chamber was taken out of the bath and left to warm at room temperature. When the pressure reached atmospheric, the chamber was opened and the vials taken for viability evaluation.

Viability was determined by observing movement within an hour from cryopreservation and, when initial motility was marginal, a subsequent examination was taken 24 hours later [104].

Results and Discussion

Fig. 65 illustrates the criterion employed to evaluate post-isochoric cryopreservation survival. It consists in random selection of observation sites and counting worms that moved during the time of observation. Fig. 65 shows excerpts from a 10 second video recording of the worms under one microscope ocular site. The frames show adult worms and L2/L3 larvae. During the 10 seconds of observation all the C. Elegans in the frame moved except the one marked with an arrow. In the different experiments some worms moved vigorously and others sluggish. In this study we evaluated only motion as a measure of viability. We observed that this measure of viability produced similar results immediately after the cryopreservation as well as 24 hours after preservation. Of importance is the observation that sluggish motion did not correlate with death after 24 hours. However, much more research is needed to evaluate the possibility of partial damage. Our criteria for viability here, was solely motion.

Fig. 65. Images from a 10 second microscope video illustrating the way we evaluated viability. In this frame and time sequence only one L2 larvae (marked with an arrow) did not move. All the other adults and L2/L3 larvae moved, which we took as a measure for viability.

Fig. 66. Display of pressure versus time during different experiments. Insert: Temperature and pressure at thermodynamic equilibrium in a constant volume system containing ice and a solution, whose initial concentration is 0.9 mg/l NaCl.

Fig. 66 shows the pressure- time history that the organisms experienced during the isochoric cryopreservation. The insert facilitates correlation between the pressure and the temperature in the two phase constant volume system. The insert also shows experimental results on the pressure-temperature correlations, that have verified our theoretical analysis [95]. Curve A, is for an experiment in which the pressure was elevated to 20 MPa (-2 ), in ten minutes. The viability evaluation taken from five different sites showed the following live/dead ratio: adults (75/0), L2/L3 larvae (354/0). Obviously, all the nematodes survival brief isochoric exposure to – 2 C. While, a depression of temperature of – 2 may appear small, any decrease in temperature is of importance in organ preservation. The normal temperature at which organs are preserved for transplantation is 4 . (This is the temperature at which the organ will eventually find itself in an ice water mixture, because the lowest density of water occurs at 4 ). Many experiments have shown the value for preservation, of even a small temperature reduction. For example, Amir et al, have shown that using antifreeze proteins to reduce the preservation temperature from 4 to – 1.3 can extend the period of preservation of a heart for transplantation from less than six hours to 21 hours [105], [97], [106]. Okamoto et al show that preservation of a lung in a supercooled state at – 2 , has substantial benefits over the preservation at 4 [107] Lungs stored using a method of lung preservation in which electric fields are facilitate supercooling, show better organ function after preservation at – 2 than conventional storage at 4°C. A recent paper has shown that liver can be transplanted after four days of preservation at – 6 with perfusion supercooling [109]. Conventional methods of liver preservation employ a temperature of 4 , and livers can be preserved at that temperature for less than eight hours. Obviously lowering the storage temperature from 4 to – 6 can substantially extend the period of preservation of organs for transplantation.

Curve B, is for an experiment in which the pressure was elevated to 45 MPa (- 4 ), in about twenty minutes. The viability evaluation taken from three different test tubes showed that the overall live/dead ratio was 138/4 and the percentage live/dead in each of the tubes was (94.4%, 100%, 98.04%). The conditions of this experiment are particularly interesting in regards to life on earth under extremes of temperature and pressure. Thorough studies were performed on the thermodynamics at the bottom of the subglacial Antarctic lake Vostok [110]. The lake is under about 3.2 km to 4.2 km of ice. The temperatures at different locations on the ice water interface in the lake range from – 2.4 to – 3.15 and the pressures of between 33.5 MPa and 43.9 MPa. Obviously the conditions that the nematode worm experienced in the experiment identified as curve B are more severe than those on the ice/water interface in lake Vostok. By wide extrapolation, this suggests that multicellular life could exist in the subglacial Antarctic lakes.

Curve C, is for an experiment in which the pressure was elevated to 65 MPa (- 6 ), and the total excursion to and from that pressure took about one hour (Figure 4). Three test tubes with samples were used in this experiment. There were few adults in this series of experiments and the live/dead ratio was 15/6 (71% survival). The ratio of live/dead in L2/L3 larvae was less 65/108; (37%survival). The worms, while moving appeared to be more lethargic than in the previous experiments. However, the ratio live/dead was similar an hour after the experiment and 24 hours after the experiment.

When comparing curves, A and C, it is obvious that the conditions in C were higher pressure and longer exposure to isochoric freezing. Therefore, in experiment D, we repeated pressure the pressure and temperature conditions from experiment A and exposed the nematodes to a length of exposure comparable to that in experiment C. To achieve these conditions, we immersed the isochoric chamber in a salt ice slush at – 4 , rather than use the Nestlab cooling apparatus. The results show that the survival of the worm was not affected by the longer exposure and it was similar to that in experiment A, 100% survival. This suggests that the organisms in experiment C succumbed to the higher pressure.

The goal of this study was to examine the survival of a multicellular organism during freezing in isochoric conditions. Survival was shown. However, there was no attempt to optimize conditions for preservation. The literature on hyperbaric preservation shows that the rate of pressure increase has an important effect on survival [111]. Lower rates of increase in pressure improve survival. Obviously much research remains to be done if the goal is to use isochoric freezing for biological matter preservation. The effect of the rate of cooling during isochoric freezing is most likely an important parameter that should be examined next.

Conclusion

In this part of the thesis, I present some conclusions over my research activity and some research trens.

Refrigeration. A refrigeration system is cooling articles, liquids, solids or gases down to and maintain them to a temperature lower than ambient. Based on this reasoning refrigeration system can be defined as heat removers. In refrigeration systems, heat is removed or more precisely transferred from the articles to be cooled by using a fluid referred as the refrigerant. Refrigeration industry has expandend in the least years and pays a significant role in societies and their economies. Global warming is changing our way of thinking and as in many fields, in case of refrigeration, the use of natural refrigerants is the right choice now. Energy efficiency is a key component for a sustainable development. Actual research is focused on improving efficiencies and reducing energy in refrigeration systems using ammonia or carbon dioxide as refrigerants. The current European regulations for the use of synthetic refrigerants, which are dangerous and toxic gases, such as R134, R410 or R407 require their total elimination from the market until 2022.

My research into the field of Refrigeration cover:

optimizing heat exchangers and other components used for this systems;

use of renewable and recoverable energy sources to drive refrigeration systems;

promoting the use of natural refrigerants;

using high-efficiency refrigeration for air conditioning;

optimizing absorption and adsorption refrigeration systems;

the study of vapor compression and absorption heat pumps used for different purposes;

optimizing key geometric parameters for refrigeration;

study of materials in cold environments;

free cooling and solar cooling;

design, experimental and performance analisys of different components.

Cryogenics. Cryogenics is the branch of science that covers the production and effects of very low temperatures. Refrigeration cover the temperature interval between positive temperatures down to -50șC. Cryogenics cover the temperature interval between -50șC and – 273,15șC (absolute zero). Cryogenics has many applications. The most spread application of Cryogenics is related to air separation and liquefaction of its components (oxygen, nitrogen, argon, krypton, xenon, helium, neon, etc.). These fluids are named by the industry as Cryogenic fluids and are often used in industrial, research and medical applications.

Another important commercial application of cryogenic gas liquefaction techniques is the storage and transportation of liquefied natural gas (LNG), a mixture largely composed of methane, ethane, and other combustible gases.

Another application is related to food preservation by using liquid nitrogen in most cases. The liquid nitrogen is sprayed over a product and immediately vaporizes, absorbing its heat content.

The electrical resistance of most metal decrease as temperature decrease and some metals lose all electric resistance and become superconductors. Superconductors have many applications. They are used in particle accelerators, in magnetic resonance imaging (MRI), electronics, magnetic levitation trains (MAGLEV), electric motors and generators. A particle accelerator is a complex installation used in high-energy physics to accelerate elementary particles. Generally, only accelerates particles carrying electric charge. Speeding is under the action of electric and magnetic fields. It is used to study elementary particles. The largest accelerator is at European Nuclear Research Center (CERN) and the minimum temperature generated there with cryogenic facilities is 0.8 K lower than the temperature of space, which is 2.7 K (-270.5șC).

Cryogenics has also an important role in medicine and is used in surgery to freeze unhealthy tissue, cell and tissue preservation, use of liquid oxygen to support life in hospitals, etc.

In 1981, Cryogenics has extended to space vehicles, when the first orbiter, Colombia shuttle was launched with a powerful rocket fueled with liquid hydrogen and liquid oxygen as propellent.

My research into the field of Cryogenics cover:

optimizing heat exchangers and other components used in air separation units;

the study of various materials at low temperatures;

optimizing insulation systems for pipe and tanks used in cryogenics;

the study, design, experimental and performance analysis of devices for tissue preservation;

the study, design, experimental and performance analysis of 3D printing for tissues and organs;

transport and preservation of food using cryogenic methods;

Heat and mass transfer in buildings. Buildings have the main function to serve as a shelter for people during periods of work, rest and relaxation or for their goods and technological processes. The buildings' sector has a major contribution to conventional fuel's consumption, used primary as energy supply, thus achieving a significant environment degradation by consuming large quantities of materials (coal, wood, etc.) and producing greenhouse-gas emissions. Buildings account for approximately 40% of energy consumption worldwide. Building design nowadays involve high efficiency and low energy consumption for the building and its building services. Understanding the fundamentals of heat and mass transfer, the behavior of air and water movements is more important than ever before. Heat and mass transfer methods used in building services design provides knowledge for the technology subjects of air conditioning, ventilation, space cooling and heating and water services.

My research into the field of Heat and mass transfer in buildings covers:

optimizing materials and envelope insulation techniques;

study of low temperature radiation systems for space cooling and heating;

study of double-skin facades as an efficient system for glass office buildings;

study of heat pump integration for family house and industrial buildings;

use of renewable and recoverable energy sources in heating and cooling systems;

Renewable-energy sources potential in our country. Population and economic growth in developing countries, is demanding high levels of energy in order to meet increasing modern life conveniences [116]. Electricity production is rising significantly in order to provide higher economic welfare, using hydropower as an advantageous alternative for clean energy at a stable price [117]. Romania is significantly decreasing its dependence on traditional fossil fuels. It is to be mentioned that hydropower is in Romania, the first main source of energy among renewable-energy sources, followed by Wind energy.

Investors in Romania prefer to develop more hydropower and wind facilities, because other alternatives (i.e. photovoltaic facilities) pose risks, climate restrictions and lack of experience.

The main period of development in the sector of hydro electricity production was 1965-1990, coinciding with the rapid development on the economy. After 1989, investments for new hydroelectric power on rivers in Romania were stopped. After this year, investments were made only for the completion of which were under execution in that year and refurbishing some existing. The main investor in the development of the hydro electricity production was the Romanian state, which after 1989 could not support the development of this sector due to the economic crisis in the early 1990. One of the ways of encouraging and developing the hydro energy production sector is by implementing aid schemes for investors and producers in this field.

Romania was in 2014 on the third place in top EU countries with the lowest energy dependency, after Estonia and Denmark. The share of electricity from renewable sources in gross electricity consumption, for Romania in 2014, was 41.7%, placing it on the 7th place in the European Union.

The wind energy in Romania witnessed considerable development over the five-year period of time. 75 wind farms with a power range from 0.008 to 600 MW and an average of 40 MW were built.

Over 1,200 wind turbines are spread on the entire surface of Romania. This development of wind farms was achieved primarily in two regions: the core in Dobrogea Plateau with near 78% (see Figure 18) of the total power installed, and a secondary one in Bârlad Plateau. The largest onshore wind farm in Europe is located in Dobrogea, in Fântânele and Cogealac, having an installed power of 600 MW [118].

My research in the field of Renewable energy sources potential in our country cover:

evaluation (review) of hydropower in Romania, as a renewable and sustainable resource of energy and as a regional focused coverage of renewable energy;

evaluation (review) of wind in Romania, as a renewable and sustainable resource of energy and as a regional focused coverage of renewable energy;

Appliacations of refrigeration and cryogenics in Bioengineering. Biological engineering or bio-engineering (including biological systems engineering) is the application of concepts and methods of biology (and secondarily of physics, chemistry, mathematics, and computer science) to solve real-world problems related to life sciences or the application thereof, using engineering's own analytical and syntheticmethodologies and also its traditional sensitivity to the cost and practicality of the solution(s) arrived at. In this context, while traditional engineering applies physical and mathematical sciences to analyze, design and manufactureinanimate tools, structures and processes, biological engineering uses primarily the rapidly developing body of knowledge known as molecular biology to study and advance applications of organisms and to create biotechnology [119].

Industry of bio-engineering extends from the creation of artificial organs by technical means or finds ways of growing organs and tissues through the methods of regenerative medicine to compensate reduced or lost physiological functions (Biomedical Engineering) and to develop genetically modified organisms, i.e., agricultural plants and animals as well as the molecular designs of compounds with desired properties (protein engineering, engineering enzymology). In the non-medical aspects of bio-engineering, it is closely related to biotechnology [119].

Cell and organ preservation for storage is important in biotechnology and medicine. It is used for diverse applications, including biological procedures that require cell line storage and medical procedures that employ preserved cells and organs for transplantation [120]. Life processes are temperature-dependent, electro-chemical reactions; whose sum is the metabolism. Similar to the kinetics of every chemical reaction, the rate of metabolism is decreased by lowering the temperature. Most enzymes of normothermic animals show a 1.5 to 2 fold decrease in metabolic activity for every 10 șC decrease in temperature [87]. Therefore, lowering the temperature is how living cells and organs are preserved in biotechnology and medicine[120]. The time of preservation increases with a decrease in preservation temperature. Many multicellular living organisms also lower their temperature to survive less than optimal environmental conditions; such as cold-blooded animals and hibernators in winter. However, life on earth takes place under atmospheric, isobaric (constant pressure), thermodynamic conditions. Under these conditions, water, which is the primary component of living matter, freezes at 0 șC when pure, and at – 0.56 șC, in an isotonic concentration. Freezing completely disrupts life processes and living material cannot survive freezing, in their native state [121].

My research into the field of Applications of refrigeration and cryogenics in Bioengineering cover:

tissue and organ preservation methods;

development of more efficient and economical methods for long-term preservation of food in a frozen state;

tissue and organ 3D printing;

development of new medical devices;

explore the possibility of life in hyoerbaric conditions.

The evolution and development plans for career development (max. 25000 characters)

My professional activity takes place in the Department of Building Services, on the Faculty of Civil Engineering, at Transilvania University of Brasov.

The development of my future career in terms of research and academic activities covers the following subjects:

Refrigeration

Cryogenics

In this academic career development proposal, I will present the stages I will go through, based on results so far.

The presentation contains the following parts:

Previous professional activity results;

Development of my academic career in terms of teaching and scientific research.

Previous professional activity results

Studies:

1987 – 1993 Licensed engineer – “Dunărea de Jos“ Galați University – Specialty Thermal Machines, Direction of deepening "Refrigeration";

2000 Specialization in Marketing and Sales Techniques

2001 – 2004 PhD in Mechanical Engineering, specialization Cryogenics, “Dunărea de Jos“ Galați University. PhD Thesis: “Cercetări privind obținerea concentratului de Kripton-Xenon în instalații de separare a aerului”.

2006 Specialization in the filed of “Personal Leadership Coaching System“

2007 Specialization certified by the Ministry of Economy in the fields of: “Technical Expert with Execution” and “Technical Expert with Quality and Extrajudicial”.

2013 Thermal power balances being supported within "Politehnica" University of Timisoara, in order to obtain certification by ANRE, thermo auditor.

Professional and academic activity:

1993 – 1999 Mechanical Engineer – Oxigen Plant, SC SIDEX SA Galați

1999 – now General Manager and CA President of SC CRIOMEC SA, Galați;

2007 – 2009 Associate Techer, Lecturer – Technical University of Civil Engineering, Bucharest, Department of Termotechnics;

2009 – now, Full Professor – ”Transilvania” University of Brașov, Civil Engineering Faculty, Department of Building Services.

After graduating as a mechanical engineer in the factory Oxygen Platform Sidex SA Galati, I participated in the design and execution activities subassemblies and parts for installations with high technological complexity.

In 1994, I founded together with a group of fellow experts, the private firm CRIOMEC SA Galati, where I transferred in 1999 to the position of CEO and chairman (acting as a holding and present).

This company has as main activity: design, manufacture, installation and repair of industrial plants, cryogenic, petrochemical and metallurgical.

Representative works which they have been coordinated within the company, are presented in the table below:

Through active participation in these projects, we have accumulated extensive experience in manufacturing technology, materials, special equipment for working at low temperatures, obtaining and separation technical gas (used in technologies for thermal, cryogenic, petrochemical, metallurgy, turbine equipment and complex equipment), which generated an impressive amount of information that could be shared later students.

During the period: 2007-2009, we conducted educational activities, as associate professor with the position of Lecturer in the Department of Thermodynamics and Thermal Equipment with responsibilities in teaching the subject – cryogenic (course and applications), students of the Faculty of Engineering installations.

As such, we tried to combine theoretical knowledge with practical engineering taught by organizing seminars and visits to various representative industrial cryogenic plants.

However, this time we developed two manuals for students and professionals working in the field of Cryogenics: “Alexandru Șerban, Florea Chiriac – „Criogenie Tehnică”- Editura AGIR, București 2006” și „Alexandru Șerban, Florea Chiriac – „Criogenie Tehnică – Echipamente: Construcție. Funcționare. Mentenanță” – Editura AGIR, București 2007 (see Fig. 67).

Fig. 67. The two manuals for learning Cryogenics

Parallel to teaching activity, I actively participated in setting up and equipping the laboratory of heat engineering and refrigeration, with performant equipment installations such as "thermostatic chamber for testing heat exchangers", "Groups Refrigeration powers of 30KW and 40 KW servicing stand for testing the performance and characteristics of construction materials and equipment", "Oven to test the fire resistance of materials and equipment used in buildings and building services", "stands to research heat exchangers with mini and micro channels", "ammonia-water absorption refrigeration system, low power, with compact heat exchangers", plus redevelopment and reconstruction of the laboratory.

Since 2009, until now, I occupied by competition, the position of Full Professor in the Faculty of Civil Engineering, Department of Building Services, at "Transilvania" University of Brasov, teaching classes and seminars with applications for disciplines: Refrigeration and Cryogenics.

As such, I focused on the modernization of subject content, teaching method and their transposed into practice. Thus, the necessary teaching materials were developed in-depth study for students, such as (see Fig. 68):

Alexandru ȘERBAN, Florea Chiriac – „Instalații frigorifice” – Seria: Cursuri Universitare. Masterat, Editura Agir, București, 2010, ISBN: 978-973-720-356-4, 246 pagini

Alexandru ȘERBAN, Chiriac F., Năstase G. – Instalații Frigorifice – Aplicații și probleme rezolvate, Editura Agir, București, 2011, ISBN: 978-973-720-425-7, 217 pagini

Năstase G., ȘERBAN Alexandru – „Proiectarea 2D cu AutoCAD”, Editura Universității Transilvania din Brașov, 2012, ISBN: 978-606-19-0106-7, 177 pagini

Năstase G., ȘERBAN Alexandru – „Fațade duble de sticlă pentru clădiri de birouri. Studiu de caz Brasov”, Editura Napoca Star Cluj-Napoca, 2014, ISBN: 978-606-690-151-2, 203 pagini

Fig. 68. Teaching books

I also perfected the method of teaching the knowledge, the interactive realizing a platform for the student refrigeration plant material available on the website: www.dralexandruserban.ro (Fig. 69 left).

Due to the success of this project, we have achieved another platform for Cryogenics, which can be accessed www.criomecsa.ro/criogenie (Fig. 69 right).

Fig. 69. Interactive platforms for learning Refrigeration and Cryogenics

Interactive teaching methods create a deeper learning, students developing thinking skills and better understanding by presenting concrete examples.

This procedure, which is part of the development trends of modern didactics methods.

In parallel to teaching briefly presented above, I participated in the design, equipment purchase, installation and commissioning of teaching stands and research facilities for students, master and PhD students. Those contributions have resulted in creation of two laboratories for teaching and research Refrigeration and Cryogenics, representative for the specialized disciplines and emblematic to the Department of Building Services at Transilvania University of Brasov (Fig. 70, Fig. 71 and Fig. 72).

Fig. 70. The laboratory of Refrigeration (left) and Absorption Heat Pump and Chiller for air conditioning purposes, installed at the Faculty of Civil Engineering Brasov (right)

Fig. 71. Heat Pump Laboratory (left) and panoramic view of Radiant Surfaces Lab (right), Building Services Department, Faculty of Civil Engineering, Brașov, Romania

Fig. 72. Box window double-skin façade laboratory

Research activity

Works in the field of Cryogenics

To this end I have developed individually and collectively over 25 works. Among the most representative works can be mentioned: the separation of krypton-xenon from the air (subject developed in the PhD thesis); regenerative cryocoolers – cryogenic cycle analysis; processes of heat and mass transfer in cryogenic equipment; fast reinstallation methods of cryogenic air separation plants.

Works in the filed of Refrigeration

We worked in collaboration with other colleagues, over 60 scientific papers and communications, which can be mentioned: Absorption refrigeration systems operated with renewable energy sources; ammonia absorption refrigeration systems-water, low power, compact heat exchangers, microchannel, plates; Study refrigeration systems with natural fluids for environmental protection.

Works in Heat and Mass transfer in Buildings and Building Services

To assess the quality of materials used in construction, establishing areas yielding high heat (in buildings, map allocators temperature in floors, walls and structural frame), the use of renewable energy in buildings, developing the concept of building a low power consumption.

In order to develop experimental research base Installations Department of the Faculty of Civil Engineering, University of Brașov, I participated actively in the design, equipment purchase, installation and commissioning of experimental stands.

Among these experimental achievements I can mention:

Faculty building air conditioning system using efficient refrigerating machines, absorption-type;

Heat pump installation with mechanical vapor compression, to supply chilled water/heat to the radiating surface laboratory;

Laboratory for testing various radiant surfaces for heating and cooling, such as radiated floors, radiant walls, ceilings and radiant temperate concrete.

These systems can be used to research teachers, and preparing the thesis of bachelor, master, doctorate by students.

My future academic career development, in terms of teaching and scientific research

Diversification of curricula and methods of transmitting knowledge

I propose that disciplines "Refrigeration" and "Cryogenics" include knowledge and numerous applications, topical, related to the profession of building services engineer, such as:

Air conditioning plant provided with efficient refrigeration systems powered by renewable energy sources (solar, geothermal), with environmentally sound refrigerants;

Refrigerators for cooling the massive concrete construction;

Refrigerators for freezing soil for underground construction;

Installation of heat pumps for efficient and environmentally friendly heating systems for greenhouses;

Presentation of small and medium refrigeration systems for residential and commercial consumers, efficient and environmentally friendly;

Refrigeration

This course aims at general knowledge, understanding concepts, theories and basic methods of refrigeration; development of professional projects using established principles and methods in the field of refrigeration. Ensure discipline in order to prepare students to design, build and operation of refrigeration systems used in the built environment. The specific objectives of the course refrigeration are: the understanding of issues related to heat transfer in refrigeration; knowledge of general aspects related to cycles of operation of various types of refrigeration systems (mechanical vapor compression, absorption, etc.); knowledge of the operating principle of refrigeration; understanding the phenomena that occur in various types of refrigerators, as applicable; understanding the phenomena that occur in displacement compressors, rotary.

During refrigeration applications of artificial cold treats and climate in the areas of air, heat pumps, artificial ice rinks, cooling concrete for massive structures and methods of freezing ground. In this way the course is also a starting point for other courses taught in the department, such as "Ventilation and air conditioning", "Heat pumps".

Technical Cryogenics

This course was born from the desire to raise the level of knowledge, to present innovative technologies and materials in the installations. Cryogenics rate shows extensive technical gas production technologies in cryogenic air separation method.

The course of Cryogenics Engineering is to train students and provide them with knowledge of technical, on the theoretical basis for obtaining very low temperatures, up to about 4K, information related to components and the main types of equipment used cooling, liquefying and gas separation. By rich material presented in this course, the numerous descriptions of various equipment allow students to become familiar with the operation, selection, calculation and dimensioning of the various components or auxiliary equipment cryogenic installations.

All these issues make a positive contribution to students' awareness of proper training, research opens new horizons side, placing the current trends in technological developments.

Teaching career and educational development

For this scope I propose:

To diversify the way of presentation and transfer of scientific information based on interactive systems. In this regard, I will continue to expand interactive teaching platform for the discipline "Refrigeration" and "Cryogenics".

Continuous upgrade and completion of specialized laboratories and modernization, while ensuring appropriate softwares; in the laboratory works will be presented actual cases encountered in gas separation technique used in high-vacuum thermal insulation, ways to assess the status of building energy and possibilities of reducing primary energy consumption;

Making internships at prestigious universities abroad, in order to exchange experience for the benefit of staff, students and the entire staff specialists;

Publication of courses, to facilitate access to specialized information to students. In this regard, I propose that the courses provide both the basics of discipline, connection with other specialties and a range of new data from my research and collective, in journals, lecturing and congresses;

To encourage students to participate in scientific research, opening them new opportunities to take part in conferences, agreements and collaborations, to specialize doctoral, all designed to broaden their technical and specialized information;

To participate alongside colleagues from the Department to realization of projects of national and European importance, supporting teamwork and collectively forming a stable and self-assertive;

Students from Bachelor, Master – will be offered follow graduation complex themes, which are contained in refrigeration, heat pumps, cryogenic. Since the Refrigeration and Cryogenics disciplines present a higher degree of difficulty, we follow braiding applications theoretical and practical lessons with visits to the sites.

Research development

Developing research will be oriented in the following directions:

Energy preservation in buildings and buildings services;

Increase of Environment Protection and Safety for People;

Low installation costs and efficient use of space for installation.

To this end will take place the following research:

Further research within the field of absorption and adsorption refrigeration type using Renewable-Energy, Solar Cooling, Refrigeration systems operated bivalent energy systems (solar and conventional energy);

Further research in the field of small and medium cold systems with compact (changing microchannel, minicanale, plates, efficient compressors), driven by non-conventional energy.

Cold Laboratory will develop, allowing research both heat exchangers in the refrigeration and heat pump equipment and systems mentioned above.

For research in the field of cryogenics, we achieve a testing laboratory materials and equipment construction and installation schemes to extremely low temperatures and variable.

Participation in National Research Projects through thorough knowledge of the methodology and their requirements.

Promotional activity and attract a greater number of students in research teams, following both their material stimulation and exploitation of knowledge gained by them in drafting graduation.

The development of scientific research will involve more active in the following areas:

attending University and Department effort to modernize and upgrade the material with systems and equipment allowing high finesse research and experimentation;

forming a united team with a high readiness, able to achieve high-level scientific results;

publishing scientific articles in journals with international recognition in the field;

presentation of research findings at conferences and scientific meetings in the country and abroad to raise awareness of refrigeration and cryogenic school in Romania;

and to enable participation in national and international research networks;

publication of books / chapters specialized in printed works belonging to internationally recognized publishers;

I am certain that these ideas and objectives regarding the development of my academic career will contribute to strengthen the position of Transilvania University of Brasov, in the hierarchy of prestigious national universities, and increasing reputation among students, on providing a solid education.

Raising standards of academic excellence will be constantly pursued and promoted in the great family of our university: students, teachers, researchers and support staff, actively involved me all initiatives to increase the importance and visibility of the University staff.

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