Dissertations / Theses on the topic 'Alternative refrigerant'

This study aimed to facilitate evaluation of alternative refrigerants for the air conditioner market. In order to achieve this target, two objectives were set. The first being the identification of alternative refrigerant with regard to regulations and trends. The second being enabling of thermodynamic evaluation of refrigerants for single components in air conditioners via design and installation of a test rig. A literature review was conducted to investigate the regulations, standards and trends for nine regions with high market shares. Furthermore, refrigerant substitutes for R410A and R22 where identified. The literature showed strong indications that a global HFC phase down is on the horizon, but that the approach and urge for such a phase down varies between regions where three main priorities could be seen; efficiency, GWP values and safety. Comparing these priorities with simulated refrigerant characteristics such as Carnot efficiency, GWP values, volumetric capacity and the liquid density using RefProp, identified alternatives. Further the literature showed that the lower flammability limit (LFL) and the amount of charge allowed were limiting factors for flammable refrigerant. There are many new refrigerants that could have less charge for the same capacity the LFL however restricts the refrigerants like R290, R441A and R443A only to be used in small systems. A test rig was designed and constructed in order to enable testing of single components in air conditioners. To verify the test rig, tests conducted with an evaporator using two refrigerants: R410A and R32. The reliability and validity of the tests was studied by comparing the results from the air side and refrigerant side, via uncertainty calculations using the GUM method and by a thermodynamic evaluation. The results of the repetition tests showed an expanded uncertainty, with a confidence interval of 95%, of 26 W for a cooling capacity of 2190W for R410A (Q̇evap,R410A=2190±26W). For R32 the expanded uncertainty was 27W for a cooling capacity of 2795W (Q̇evap,R32=2795±27W). Also the test rig was verified to be used for analyzing detailed evaluation of evaporators such as looking at heat transfer and the differential pressure drop. Further the study presented six conclusions: When evaluating refrigerants regional priorities between efficiency, safety and GWP values, refrigerant characteristics and type of unit need to be considered. Safety standards need to be more acceptable towards flammable refrigerants in order to meet low GWP targets. The change in market trends leads to new roles for the refrigerant and compressor suppliers and put higher demand on air conditioner manufacturers to consider refrigerant characteristics in product development. The importance of experimental thermodynamic evaluation on refrigerants effect on single components is increasing. Performance of different refrigerant for single components can be evaluated for optimizing cycle performance. Leapfrogging in the developing world can lead to a faster introduction of low GWP refrigerants.

HCFC-22 is the world�s most widely used refrigerant. It serves in both residential and commercial applications, from small window units to large water chillers, and everything in between. Its particular combination of efficiency, capacity and pressure has made it a popular choice for equipment designers. Nevertheless, it does have some ODP, so international law set forth in the Montreal Protocol and its Copenhagen and Vienna amendments have put HCFC-22 on a phase out schedule. In developed countries, production of HCFC-22 will end no later than the year 2030. Zeotropic blend HFC-407C has been established as a drop-in alternative for HCFC-22 in the industry due to their zero Ozone Depletion Potential (ODP) and similarities in thermodynamic properties and performance. However, when a system is charged with a zeotropic mixture, it raises concerns about temperature glide at two-phase state, differential oil solubility and internal composition shift. Not enough research has been done to cover all aspects of alternative refrigerants applications in the systems. This research intended to explore behavior of this alternative refrigerants compare to HCFC-22 and challenges facing the industry in design, operation service and maintenance of these equipments. The purpose of this research is to investigate behavior of R407C refrigerant in chiller systems. This includes performance and efficiency variations when it replaces R22 in an existing system as well as challenges involved maintaining the system charged with R407C. It is a common practice in the industry these days to evacuate and completely recharge when part of the new refrigerant blend was leaked from the system. This has proved to be extremely costly exercise with grave environmental ramifications. This research is intended to address challenges faced in the real world and practical terms. Theoretical and experimental approaches used as a methodology in this work. The system mathematically modeled to predict detailed system performance and effect of the leak at various conditions. To make this feasible and accurate enough, two separate approaches made, first system performance for pure R22 and R407C, and second system subjected to range of leak fractions. The earlier model was relatively straight forward when compared to the latter. Modeling a system charged with R407C ternary mixture and subjected to range of leaks posed enormous challenges. A sophisticated experimental test apparatus was also designed and built. Comprehensive and detailed tests at various conditions were conducted with special attention on instrumental accuracy and correct methodology. The first part has been successfully modeled and predicted all the factors and performance with excellent accuracy when compared to the test results. In these approaches pure refrigerants R22 and R407C were used and simulated the system behavior at range of conditions. However, the second part was the most challenging ever. Comprehensive leak process simulations produced trends of R32/R125/R134a composition change as function of rate of leak. Starting from this point, equations have been created to represent the composition change as function of percentage of the leak. The system thermodynamic cycle was also modeled to calculate capacity, power input and COP at the range of the conditions. Despite many affecting parameters and complexity of the model, the mathematical model successfully predicted the test outcome with a very reasonable accuracy, averaging around 3% with some times reaching to 5 to 6%. On the experimental stage the system charged with the new HFC-407C was deliberately subjected to refrigerant leak at various leak stages. The aim was to objectively determine to what extend the gas leak can be still acceptable without going through the expensive complete gas charge. The effect of leak was tested and verified at 10% steps, from 10% up to 50% mass fraction for the total charge. It has been observed that at the leaks beyond 30%, the adverse effect on the capacity becomes more significant, from 8 to about 15% decrease. While the power input decreased at slower pace, from 3% up to about 8% depending on the test conditions. This translated to COP decrease ranging from 4 to about 7%. This capacity loss and efficiency decrease are significant figures which suggests that the system, here chiller, can not be allowed to degrade the performance to that extend and still continue operating.

This thesis deals with issues of heat pumps for air conditioning purposes. Mainly addresses itself with physical principles of heat pumps and with division of heat pumps according to natural resources, from which they draw heat energy. The next part of this thesis dedicates itself to experimental measurement of air conditioning unit, which in winter time operates on the principle of heat pump. The last part of this thesis is focused on design of two options of employment of heat pumps as sources of heat and coldness for a central air handling unit, which regulates incoming air for a dining room in a retirement home in Brno.

The European Parliament has shown its legislative capabilities by adopting a tough approach on the reduction of fluorinated gases (F-gases). The EU Regulation No 517/2014, will phase out F-gases with high global warming potential (GWP) within a well-defined step down time schedule. This will affect refrigerants which are commonly used in commercial cooling applications. While the time schedule implies existence of replace- ment refrigerants, the market continues to develop alternatives for the refrigerants already in deployment. Though the R404A,which is a commonly used refrigerant in station- ary cooling applications, will be prohibited of use 1 January 2020. In this paper, the two alternatives R448A from Honeywell and R449A from DuPont were compared to the R404A baseline, within a theoretical model with empirical compressor and system input data. The key points of comparison were cooling capacity, compressor discharge temperature, coefficient of performance (COP) and total equivalent warming impact (TEWI). The outcome of the model showed a decrease in cooling capacity for both alternatives, as well as an overall increase in compressor discharge temperature. For low evaporator temperatures, a decrease in COP was present and vice versa for high evaporator temperatures, both for medium and high condenser temperature. However, the TEWI for the both refrigerants, showed a decrease in carbon dioxide (CO2) equivalent emissions during the refrigerant system lifespan, running on both R448A and R449A, regardless of which European country the electricity was produced in.
Det Europeiska Parlamentet har visat sin lagstiftande förmåga i och med antagandet av en tuff förordning om reducering av F-gaser. EU Förordningen Nr 517/2014 kommer att fasa ut flourinerade gaser med högt GWP värde och det med en väl definierad nedtrappningsperiod. Detta kommer bland annat att påverka köldmedier som ofta förekommer i kommersiella kylapplikationer. Medan tidsschemat förutsätter redan existerande ersättare fortsätter marknaden att utveckla alternativ för de köldmedier som idag är i bruk, samtidigt som användandet av det vanligt förekommande kylmediet R404A kommer att förbjudas i och med 1 januari 2020. I den här rapporten jämförs de två alternativa kylmedierna R448A från Honeywell och R449A från DuPont i en teoretiskt modell, med empiriska data för kompressor- och systemvariabler, där kylmediet R404A används som referens. Huvudsakligen jämfördes kyleffekt, kompressorns utströmningstemperatur, COP och TEWI. Resultaten från modellen visade en minskad kyleffekt för båda de båda alternativen, såväl som en ökad utströmningstemperatur för kompressorn. Låga evaporatortemperaturer resulterade i en minskning av COP och vice versa för höga evaporatortemperaturer, både för mellan och hög kondensortemperatur. Dock konstaterades för TEWI, en minskning av de sammanlagda CO2 ekvivalenta utsläpp under kylsystemets livslängd, under drift på både R448A och R449A oavsett i vilket Europeiskt land elektriciteten producerats i.

When running a refrigeration system, the refrigerant will always leak into the atmosphere in various ways. The leakage of currently used refrigerants have a non-negligible impact on the global warming. The European Commission recently approved the Regulation No 517/2014 on fluorinated greenhouse gases (FGR). This regulation implies, among other, that refrigerants with GWP of 2500 or more will be restricted from being used in stationary refrigeration equipment being placed on European refrigeration market. In this study a number of new refrigerants are analysed and evaluated as potential replacements for R404A which is a popular commercially used refrigerant with high global warming potential. A few refrigerants from different manufacturers have been evaluated using a computer model of a basic vapour-compression system, as well as analysed from the position of refrigerant safety. It was found that the best short term replacement for R404A are two refrigerants called R448A and R449A and the best long term replacement is DR7.
I ett kylsystem kommer köldmediet alltid att, på ett eller annat sätt, läcka ut i atmosfären. Läckage av all världens köldmedium har en icke försumbar inverkan på den globala uppvärmningen. Den europeiska kommissionen nyligen godkänt en förordning kallad Regulation No 517/2014 on fluorinated greenhouse gases (FGR). Denna förordning innebär, bland flera saker, att kommersiella köldmedium med en global uppvärmningspotential på 2500 eller mer kommer att förbjudas för användning i stationära kylsystem. I denna studie har ett antal nya köldmedier analyserats och utvärderats i syfte att hitta ersättare till R404A vilket är ett populär kommersiellt köldmedium med en hög global uppvärmningspotential. Jämfört med R404A har nya köldmedier from olika producenter utvärderas i en databaserad modell av ett enkelt kylsystem för att utvärdera deras effektivitet. Studien fokuserar också på säkerhet kring köldmedier och tillsammans med resultaten från modellen framkom det att på kort sikt är det bästa alternativet för att ersätta R404A är två köldmedium kallat R448A R449A och på lång sikt ett köldmedium kallat DR7.

This thesis addresses the general subject of implementation of refrigerants that are alternatives for ozone depleting substances. In particular it covers three topics, which are environmental assessment, system performance and safety aspects related to flammability. The first Part examines the current means of assessing the global wanning impact of systems, and proposes an improved approach. The second Part presents a new balancing technique for designing systems that use refrigerants with a temperature glide, as an advancement over the conventional technique for pure refrigerants. The third Part derives a quantitative risk assessment model to be employed for evaluating the safety of hazard of flammable refrigerants. The concept of'Total Equivalent Warming Impact'' is introduced in Part 1, which is currently used by manufacturers, installers and end-users of refrigerating systems to evaluate the contribution to climate change resulting from energy consumption and refrigerant leakage. It was found that existing methods rely on many assumptions, so a thorough approach was proposed to assess the relevance of the assumptions and providing ways of avoiding them. An alternative measure for interpretation of consequences of greenhouse gas emissions is also included. Part 2 investigated the existing approach for rating and balancing sy stem components, which were found to be incompatible when applied to zeotropic refrigerants. Differences in the performance of components using pure and zeotropic refrigerants were identified, and so a new method for component rating and an advanced system balancing technique were developed based on the properties specific to zeotropes. Within Part 3, a framework for calculating ignition frequencies and consequences of a release of hydrocarbon refrigerant is presented. A major element of these calculations is the evaluation of certain quantities of the flammable mixture, and the model developed for this purpose w as based on the results from a series of gas dispersion experiments.

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Há uma crescente preocupação mundial a respeito da destruição da camada de ozônio envolvendo a terra. Os CFCs, como o R-12, foram identificados como de alto poder destruidor da camada de ozônio (ODP), pela presença de cloro em sua estrutura. Os HCFCs, como o R-22, por possuírem cloro em sua estrutura, devem ser substituídos como fluidos refrigerantes. Na Europa, equipamentos novos não são produzidos com o R-22 desde dezembro de 2003. Justamente pela ausência de átomos de cloro em sua estrutura, os hidrocarbonetos apresentam um potencial de depleção de ozônio (ODP) zero. Estudos indicam que o coeficiente de performance (COP) de unidades de refrigeração utilizando propano ou misturas com propano chegam a ser mais altos que em unidades usando R-12. Esse fato, juntamente com seu baixo GWP (Potencial de efeito estufa, que compara a massa do gás com uma mesma massa de CO2), fazem do propano e de misturas de compostos hidrocarbono bons candidatos a refrigerantes alternativos. O objetivo deste trabalho é fazer uma análise comparativa da capacidade de refrigeração e do COP em condicionadores de ar do tipo janela (C.A.J.) utilizando R-600a (isobutano), R-290 (propano) em comparação ao R-22. Uma unidade condicionadora de ar tipo janela foi testada, utilizando-se diferentes massas de R290 e R-600a. Foram realizados testes em ambiente real e em um túnel climatizado, adaptado para o presente estudo. Os resultados indicaram que o R290 é um candidato ideal a substituto do R22 em unidades de ar condicionado tipo janela, mostrando COP e capacidade de refrigeração compatível com o R22. Como suporte às análises experimentais, foi realizada uma análise termodinâmica do ACJ, com equações trabalhadas no EES (Engineering Solver Equation)

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Mecânica.
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O conhecimento do processo de lubrificação das partes móveis dos compressores alternativos herméticos, sobretudo do pistão, é de importância fundamental na concepção de sistemas de refrigeração mais eficientes. A existência de uma pequena folga entre o pistão e o cilindro permite que movimentos radiais do pistão afetem a espessura do filme lubrificante e o regime de lubrificação do conjunto. Adicionalmente, os fenômenos de cavitação e restauração do filme considerando a interação óleo/refrigerante ainda não são totalmente compreendidos e merecem mais estudos para que melhorias no projeto do compressor sejam atingidas. Neste contexto, o presente trabalho propõe um estudo teórico e experimental do escoamento de óleo e refrigerante pela folga pistão-cilindro de compressores alternativos utilizados em sistemas de refrigeração de pequena capacidade. Inicialmente é proposta a construção de uma bancada para estudo experimental das características do escoamento na geometria da folga pistão-cilindro com o pistão estático. A bancada experimental é composta por uma seção de teste com um pistão e um cilindro transparente instrumentado com sensores de pressão e termopares em diversos pontos. O cilindro é apoiado sobre um conjunto de plataformas acionadas por micrômetros que permitem que a pressão do escoamento seja medida em várias posições para diferentes graus de desalinhamento entre o pistão e o cilindro. A análise teórica engloba três modelagens distintas. O primeiro modelo descreve o escoamento bifásico da mistura em equilíbrio local na geometria da folga para a situação onde o pistão é mantido estático. As equações de Reynolds e da conservação da energia foram resolvidas numericamente considerando a variação da propriedades físicas das fases para a determinação das distribuições de pressão e temperatura do escoamento. Os resultados obtidos foram comparados com os dados experimentais medidos na bancada, com o intuito de validar o modelo. O segundo modelo estende a metodologia anterior para descrever a lubrificação dinâmica do pistão, onde os movimentos do pistão e a transferência de calor no filme lubrificante foram incorporados. Parâmetros relativos ao movimento do pistão como a potência consumida e vazamento de refrigerante pela folga foram obtidos e comparados com os calculados por modelos que consideram o filme isotérmico. Por último, o terceiro modelo envolve a caracterização do processo de crescimento de bolhas individuais em misturas óleo-refrigerante submetidas a descompressões isotérmicas, onde as hipóteses de equilíbrio mecânico e termodinâmico são suspensas. Este modelo é apresentado como uma ferramenta promissora para a descrição do crescimento de bolhas que pode ocorrer no filme lubrificante relacionado à cavitação, e da formação de espuma no cárter durante a partida do compressor.
A detailed knowledge of lubrication process in reciprocating compressors, particularly the piston assembly lubrication, has a fundamental role in the design of more efficient refrigeration systems. A radial clearance between the piston and the cylinder walls allows piston oscillatory radial movements that affect both the lubricant film thickness and the lubrication regime. Furthermore, cavitation and restoration of the lubricant film considering the oil/refrigerant interaction are not totally understood and these issues deserve additional studies for future improvements in the design of compressors. With this in mind, this work proposes a theoretical/experimental study of the ow of oil and refrigerant through the piston-cylinder clearance of reciprocating compressors used in small capacity refrigeration systems. Firstly, the project of a experimental apparatus is proposed to study ow characteristics in the piston-cylinder geometry with the piston steady. The apparatus consists of a test section in which the piston is placed inside a translucent cylinder equipped with thermocouples and pressure sensors at defined positions. The cylinder is mounted upon a set of micrometerguided stages that allows pressure measurements at several positions for different piston-cylinder misalignment degrees. Theoretical analysis includes three different models. The first one is an equilibrium model to describe the two-phase ow of the mixture through the clearance in which the piston is steady. The Reynolds and the energy conservation equations were solved numerically considering the variation of the physical properties in both phases in order to calculate the film pressure and temperature. The numerical results were compared with the experimental ones in order to validate the model. The second model extends the previous methodology to describe the piston dynamic lubrication in which piston movements and the heat transfer effect in the film were considered. The performance parameters related to piston movement, such as the power consumption and refrigerant leakage, were obtained and compared with those ones calculated by isothermal models. Finally, the third model regards characterization of growth process of individual bubbles in oil-refrigerant mixtures under isothermal depressurization, in which assumptions of mechanical and thermodynamic equilibrium were suppressed. This model is introduced as a potential tool to predict bubble growth that may occur as a result of cavitation in film, and the foamming process in the oil sump during compressor start-up.

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Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
Cada vez mais o mundo est? adotando uma matriz energ?tica limpa e sustent?vel, com o uso da agricultura para produ??o de agroenergia e combust?veis verdes, como bioetanol e biodiesel. A produ??o do biodiesel gera um coproduto, a glicerina, em que as usinas produtoras t?m dificuldades com o destino do seu excedente. V?rias pesquisas est?o sendo desenvolvidas para nortear diferentes usos do glicerol (glicerina pura). O glicerol possui total solubilidade com a ?gua e pode ser usado como aditivo anticongelante aplicado como fluido refrigerante secund?rio, em sistemas de refrigera??o indireta e com termoacumula??o. Tamb?m, o glicerol ? uma mat?ria-prima alternativa na produ??o de propilenoglicol, um ?lcool de grande aplicabilidade industrial inclusive como anticongelante. Por?m, o melhor ?lcool anticongelante ? o etilenoglicol, um ?lcool t?xico derivado do petr?leo. As solu??es ?gua-glicerol (AG) e ?gua-propilenoglicol (AP) possuem propriedades termof?sicas de qualidade inferior e desequilibradas se comparadas ?s solu??es ?gua-etilenoglicol (AE). Desta forma, esta pesquisa inovadora teve como prop?sito o desenvolvimento e a caracteriza??o de solu??es tern?rias ?gua-glicerol-propilenoglicol (AGP) como fluidos secund?rios, com propriedades termof?sicas desej?veis e competitivas com as solu??es ?gua-etilenoglicol. Equa??es preditivas simplificadas foram usadas para prever o comportamento das solu??es AGP, onde as seguintes propriedades termof?sicas foram avaliadas e estimadas teoricamente: ponto de congelamento, massa espec?fica, calor espec?fico e condutividade t?rmica. As concentra??es para definir o ponto de congelamento das solu??es AGP foram definidas a partir da Lei de Raoult das propriedades coligativas. A an?lise matem?tica inicial mostrou que as solu??es AGP possuem propriedades mais equilibradas que as solu??es AG e AP e competitiva com a solu??o AE. A comprova??o experimental das solu??es AGP foi feita a partir de ensaios para verificar suas propriedades (massa espec?fica, condutividade t?rmica e viscosidade din?mica), comparando com as solu??es de refer?ncia AG e AP. Os resultados experimentais comprovaram as expectativas iniciais e viabilidade t?cnica do novo fluido secund?rio tern?rio. A grande vantagem dos fluidos AGP ? que s?o at?xicos e derivam de fontes renov?veis

Este trabalho apresenta os resultados da pesquisa "Análise do Escoamento de Fluidos Refrigerantes Alternativos ao HCFC 22 em Tubos Capilares Adiabáticos", desenvolvida para obtenção do título de Doutor em Engenharia no Departamento de Engenharia Mecânica da EPUSP. Essa pesquisa foi motivada pelas resoluções do Protocolo de Montreal, que prevêem a eliminação gradativa do HCFC 22 e, conseqüentemente, impõem a necessidade da realização de estudos sobre o comportamento de fluidos alternativos ecologicamente aceitáveis nos sistemas de refrigeração e seus componentes. Até o momento, as pesquisas e as referências bibliográficas indicam a utilização de misturas zeotrópicas e quase-azeotrópicas como a melhor alternativa para substituição do HCFC 22. Desta forma, foi realizado um extenso levantamento experimental do escoamento do R-407C (uma mistura zeotrópica) e do R-410A (uma mistura quase-azeotrópica) através de tubos capilares, em uma unidade laboratorial construída para essa finalidade. Esse levantamento, realizado para condições de entrada subresfriada e saturada, caracterizou a influência destes fluidos refrigerantes e dos diversos parâmetros operacionais e geométricos no comportamento do tubo capilar em sistemas de refrigeração. Foram desenvolvidos dois modelos (fases separadas e homogêneo) para a modelagem matemática do escoamento de fluidos refrigerantes através de tubos capilares, a fim de verificar o efeito do tipo de escoamento adotado nessa modelagem. A validação dos programas de simulação desenvolvidos, tanto para os dados experimentais obtidos no presente trabalho quanto para dados de literatura, mostra que os dois modelos podem ser utilizados para essa modelagem, apresentando desvios semelhantes em relação aos dados experimentais. A fim de aprimorar os modelos, é necessária a realização de estudos mais aprofundados sobre o atraso de vaporização e a ocorrência de blocagem na saída do tubo capilar. Por fim, foi realizado um estudo numérico comparativo do desempenho do HCFC 22 e dos alternativos R-407C e R-410A, que indicou que o primeiro é adequado tanto para o "retrofit" de equipamentos existentes quanto para utilização em novos equipamentos, enquanto que o segundo deve ser utilizado apenas em novos equipamentos.
This work presents the results of the research activities on the "Analysis of HCFC 22 Alternatives Flow Through Adiabatic Capillary Tubes", developed at the Mechanical Engineering Department of Escola Politécnica da Universidade de São Paulo. Such research was motivated by the resolutions of Montreal Protocol, which imposes gradational elimination of several refrigerants, among them HCFC 22. This leads to the necessity of carrying out studies on the behaviour of ecologically acceptable refrigerants in refrigeration systems and components. So far, researches and literature indicate the usage of zeotropic and near azeotropic refrigerant mixtures as the best alternative to HCFC 22. Therefore, it was performed an extensive experimental survey on R-407C (a zeotropic mixture) and R-410A (a near azeotropic mixture) flow through capillary tubes. Such survey, which was carried out for both subcooled and two-phase inlet conditions, characterised the influence of these refrigerants, as well as the several operating and geometric parameters on the behaviour of capillary tubes used in refrigeration systems. In order to analyse the effect of different approaches for two-phase flow, it was developed two models (separated flow model and homogeneous model) for mathematical simulation of refrigerant flow through adiabatic capillary tubes. Models validation using both experimental and literature data shows that the two models are suitable for such simulation, with the same error level in relation to experimental data. It was also noticed that it is necessary to perform more comprehensive studies on the delay of vaporisation and capillary tube outlet shocking flow phenomena. Finally, it was performed a comparative study on the performance of HCFC 22, R-407C and R-410A, which indicates that R-407C is suitable both for retrofitting actual equipment and for new ones, while R-410A is suitable only for new equipment.

I Kraftringens geotermianläggning cirkulerar köldmediet R134a som är en fluorerande växthusgas med relativt hög GWP (Global Warming Potential). När den nya F-gasförordningen trädde i kraft 2015 resulterade det i att priserna ökade markant på de köldmedierna med hög GWP. Kraftringen vill därför undersöka vilka konverteringsalternativ det finns till R134a, dels för att minska på kostnaderna men också för att minimera verksamhetens klimatpåverkan.   Olika köldmedier har jämförts med avseende på hur de påverkar anläggningens prestanda. Det har också undersökts vilka köldmedier som ligger inom rätt tryck med hänsyn till vad kompressorn och anläggningens rör är konstruerade för. Undersökningen har gjorts genom teoretiska beräkningar som är grundade på uppmätta värden från när värmepumparna går på maximal belastning. Vid urvalet av köldmedier har det utgåtts från samma förångningstemperatur och kondenseringstemperatur som vid mätningen.   I undersökningen fann vi två köldmedier, R152a och R450A, som skulle fungera som konverteringsalternativ i avseende att de ligger inom rätt tryck och temperatur. Båda alternativen har lägre GWP och en högre värmefaktor än nuvarande köldmediet R134a. Dock är R152a brandfarligt och har högre säkerhetsklass än de två andra medierna.
In the geothermal plant of 'Kraftringen' the refrigerant R134a, which is a fluorescent greenhouse gas with relatively high GWP (Global Warming Potential), circulates. When the new F-Gas regulation was introduced in 2015, it resulted in a significant price increase for high-pressure GWP refrigerants. 'Kraftringen' therefore wants to investigate which conversion options there are for R134a, partly to reduce costs, but also to minimize the climate impact of the business.   Different refrigerants have been compared with regard as to how they affect the plants performance. Moreover, it has been investigated which refrigerants are in the correct pressure range with regard to what the plants compressor and pipes are designed for. The survey has been done by performing theoretical calculations based on measured values from when the heat pumps operate at maximum load. In the refrigerant selection process, the same evaporation and condensation temperature as during the measuring was used.   In the study we found two refrigerants, R152a and R450A, which would serve as conversion options in terms of them being in the correct pressure and temperature range. Both options have lower GWP and a higher heat factor than the current refrigerant R134a. However, R152a is flammable and has a higher degree of safety than the other two refrigerants.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Os refrigerantes CFCs (clorofluorcarbonos) como o R-12, foram identificados como de alto poder destruidor da camada de ozônio que protege a superfície da terra, devido à presença de cloro em sua estrutura. Os HCFCs (hidroclorofluorcarbonos) como o R-22, por possuírem cloro em sua estrutura, também devem ser substituídos como fluidos refrigerantes. Na Europa, equipamentos novos não são produzidos com o HCFC-22, desde dezembro de 2003. Diante da necessidade de substituição desses gases nocivos ao planeta, os hidrocarbonetos (HC) apresentam-se como bons candidatos a fluidos refrigerantes alternativos, pela ausência de átomos de cloro em sua estrutura e por não destruírem a camada de ozônio. Esses fatos, aliados a um baixo potencial de causar aquecimento global, fazem dos hidrocarbonetos bons candidatos ao uso em sistemas de refrigeração. Como contribuição a esse tema, a presente dissertação analisa experimentalmente os sistemas de refrigeração por compressão a vapor de um bebedouro e de uma câmara frigorífica, representantes das classes de refrigeração doméstica e comercial, ambas de pequeno porte. Os sistemas estudados foram testados com os fluidos refrigerantes (hidrocarbonetos): propano (R-290),isobutano (R-600a) e uma mistura de ambos em substituição aos fluidos originais dos sistemas testados, o R-22 e o R-12. Todos os testes foram realizados em condições normais de operação. Os resultados experimentais indicam que a mistura propano e isobutano mostra-se como a melhor opção como fluido alternativo em sistemas de refrigeração de pequeno porte utilizadores do R-12 ou R-22. Em segundo lugar apresentou-se o R-600a. Na comparação individual, o R-600a mostrou-se como a melhor opção para sistemas de refrigeração de pequeno porte ao invés do R-290. Porém, para sistemas de médio porte originalmente projetados para R-22, o R-290 aparece como a melhor opção

碩士
國立成功大學
化學工程學系
86
In order to achieve even higher heat transfer rate of computer chips the use of the phase-change liquid immersion cooling has been considered. As the name implies, direct liquidimmersion cooling brings the coolant into direct physical contact with the chips or electronic packages to be cooled. Consequently, it is important that the coolants used exhibit dielectriccharacteristics which do not adversely effect circuit delay. Equally important, the coolant must be chemically compatible with the electronic package materials which it will come in contactwith. Limiting the choice of coolant to a few fluids, many of which, the chlorofluorocarbons(CFC), are already being baned for environmental considerations (depletethe ozone layer). This definitely calls for accelerated development of new alternative refrigrants(hydrochloroflurocarbon, HCFC or hydroflurocarbon, HFC).In this paper, phase-change liquid immersion cooling will be studied by carrying out boiling heat transfer experiments in pure and binary alternative refrigerants. The potential of binary alternative refrigerant mixtures as coolants lies on the possible widely varied thermodynamic properties of mixtures. Boiling curves will be obtained by steadily heating a tube or a plate in liquids. Onset of nucleate boiling and nucleate boiling heat transfer rates will then be determined from these boiling curves. Theoretical analysis will also be made on boiling phenomena of binary refrigerant mixtures. As the result of experiments , the highly wetted liquids result in serious thermal hysteresisand increasing superheats of boiling incipience. By the results of theoretical analysis andexperiments, these superheats of boiling incipience are under the influence of contact anglehysteresis. The mass diffusion effect factor of R-11/R-141b is weaker than ethanol/water and NPA/water. Because of the mass diffusion effect, the heat transfer coefficients of those binary mixtures of R-11/R-141b are lower in both nucleate boiling in a narrow space and in conventional nucleate boiling. Superheats of the heating plate are changed with the widths of the narrow space. By increasing the widths of the narrow space, superheats of the heating plate increase to a maximum then decrease to a minimum and finally increase to a stable temperature . When the width of the narrow space is smaller ,the inferference body touches the unevenheating plate lightly. Heat flux from the heating plate conducts to the inferference body. By decreasing the width of the narrow space, contact areas increase and superheat decreases.When the width of the narrow space is large enough , the inferference body can*t touch theheating plate. The narrow space is covered by gas. Liquid can not flow into narrow space and superheat increases to a maximum. When the width of the narrow space increases continually , liquid flows into the narrow space and superheat decreases to a minimum. Because of microlayer evaporation and thin liquid film flow, the heat transfer coefficient of nucleate poolboiling in the narrow space is greater than that of conventional pool boiling. Finally the effect of the narrow space is smaller and smaller, and the boiling phenomena is the same as conventional nucleate boiling.

碩士
中華大學
科技管理研究所
92
With the awareness of environmental protection, refrigerants used by the past refrigeration and air condition industries may be banned. If the industries can’t search the overall solution, they must face the pressure of environmental protection and social conscience. Therefore, under the awareness of global environmental protection, to search for and develop innovative technology of alternative refrigerant is currently the industries’ important task. This study attempts to construct indicator system of new alternative refrigerant technological development through experts and scholars of different territories in Japan and Taiwan. And to investigate the future developed trend of new alternative refrigerant technology rely on analyzing relative importance of indicators by using Analytic Hierarchy Process. The results of this study indicated that to develop new alternative refrigerant technology must to considerate technological attributes and economic benefits, and furthermore to strengthen safe and environmental indicators of ecological environmental protection and industrial laws and regulations is more important.

碩士
國立臺灣大學
機械工程學研究所
89
This paper mainly discusses flow characters of the R407C refrigerant in the capillary tube by using computer numerical simulation, and make a comparison with experimental data in early papers. Theoretical analysis is divided into two important parts:1.Mixing:since R407C is not co-boiling mixing refrigerant, we must clearly confer related thermodynamics properties of every species after mixing in the two-phase region. And then we can correctly simulate two-phase changes of R407C；2.Construct governing equations of flow in the capillary tube. On the basis of former researches and governing equations listed in early papers, we make up those useful data and then construct related equations of physical phenomenon simulation in the capillary tube. So we can obviously and accurately build whole R407C flow phenomenon in the capillary tube. Because R407C is a short-time substitute of R22,we also mention about similarity and difference of R22 and R407C systematically in the capillary tube with simulation and early papers to make preliminary analysis.

碩士
東南科技大學
機械工程研究所
104
This study used R32 refrigerant in a small R410A split air conditioner (SAC) to evaluate the performance and feasibility of using these different mass (300g, 400g, 500g, 600g, and 700g) R32 alternative refrigerants by conducting the power consumption, the cooling capacity and the energy efficiency ratio (EER) tests. The experimental setup was based on the charged mass of R410A refrigerant is 700g, the power consumption is 0.909kW, the cooling capacity is 2.28 kW, and the EER is 2.6. The research successfully developed the alternative procedure of a small R410A SAC, and it proved improve system performance and achieve energy-saving. The results of the tests revealed when the optimal charged mass of R32 refrigerant is 400g, the power consumption is reduced by 8.7%, the CC is increased by 35%, and the EER is raised by 43.8%.