Dissertations / Theses on the topic 'Compression refrigeration system'

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-07-25T23:39:27Z No. of bitstreams: 1 CARLOS EDUARDO DA SILVA ALBUQUERQUE – DISSERTAÇÃO (PPGEM) 2017.pdf: 4080439 bytes, checksum: 940fff54d861725d16972dec4bb0ee8c (MD5)<br>Made available in DSpace on 2018-07-25T23:39:27Z (GMT). No. of bitstreams: 1 CARLOS EDUARDO DA SILVA ALBUQUERQUE – DISSERTAÇÃO (PPGEM) 2017.pdf: 4080439 bytes, checksum: 940fff54d861725d16972dec4bb0ee8c (MD5) Previous issue date: 2017-03-17<br>CNPq<br>Esta pesquisa apresenta uma análise energética e exergética de uma unidade de refrigeração de água gelada de grande porte, chamada chiller. O refrigerador em estudo realiza o ciclo termodinâmico de refrigeração com auxílio de um compressor mecânico, usualmente acionado por um motor elétrico, de forma a aumentar a pressão em determinada fase do ciclo termodinâmico do sistema, o que gera um alto consumo de energia elétrica. Com avanço da tecnologia, a cada dia surgem novos tipos de compressores que possuem um menor consumo de energia e melhoram o desempenho da unidade como um todo. O objetivo deste trabalho é avaliar os comportamentos energético e exergético, baseados respectivamente na primeira lei e na segunda lei da termodinâmica, de um chiller que fornece água gelada e trabalha com um compressor tipo parafuso. Este estudo foi realizado baseando-se no comportamento real de um chiller de compressão de vapor, instalado em um shopping da região de João Pessoa-PB. Através de simulação numérica, foi possível avaliar o comportamento do equipamento com a mudança de alguns dos parâmetros normais de trabalho, como pressões de condensação e evaporação, temperatura s de condensação e evaporação e fluido refrigerante. Neste estudo, são apresentados dados do desempenho do equipamento em função das pressões do evaporador e do compressor, da temperatura de evaporação, entre outros parâmetros. Os resultados das simulações, realizadas com auxilio do software EES, mostraram que o desempenho da unidade melhora ao diminuir a variação de pressão entre o condensador e o evaporador e que as eficiências energética e exergética sofrem um acréscimo com o aumento da temperatura de evaporação e uma redução com a elevação da temperatura de condensação.<br>This research presents energetic and exergetic analysis of a water refrigeration unit, called Chiller. The Chiller under study performs the thermodynamic cycle of the refrigeration with the assistance of a mechanical compressor, usually triggered by an electric motor, in order to increase the pressure in a certain stage on the thermodynamic cycle of the system, which generates high energy consumption. However, with the advance of the technology, every day emergs new types of compressors that have lowest energy consumption and improves the performance of the unit as a whole. The purpose of this work is to evaluate both e nergetic and exergetic behavior, of a chiller that provides cold water and works with a screw type compressor, based on the first and second laws of thermodynamics . This study was based on the actual behavior of a steam compression chiller from a mall in the city of João Pessoa-PB. Through numerical simulation, it was possible to evaluate the behavior of the equipment with the change of some of the normal parameters of work, as condensation and evaporation pressures, condensation and evaporation temperature and refrigerant fluid. In this study, the performance of the equipment data is presented as a function of the evaporator and compressor pressures, the evaporation temperature and other parameters. The results of the simulations, that were realized with support of software EES, showed that the unit performance was improved by decreasing the pressure variation between condenser and the evaporator and also has proved that the energetic and exergetic efficiences are increased by raising the evaporation temperature and a reduction happens by increasing the condensation temperature.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO<br>COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR<br>CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>PROGRAMA DE EXCELENCIA ACADEMICA<br>Em sistemas de refrigeração por compressão de vapor, o projeto adequado dos circuitos para o refrigerante nos trocadores de calor pode ter um impacto significativo no seu coeficiente de performance (COP). O projeto otimizado dos circuitos de refrigerante em sistemas de refrigeração com trocadores de calor do tipo tubo-aletado não é trivial, devido à complexidade de sua representação assim como o elevado número de possíveis combinações, mesmo quando metodologias inteligentes de otimização são empregadas. No presente trabalho propõe-se uma nova metodologia para a otimização simultânea (condensador e evaporador) dos circuitos do refrigerante em sistemas de refrigeração com trocadores de calor de tipo tubo-aletado. Esta metodologia, aqui denominada como GAFIS (Genetic algorithms applied in filtered spaces), mostra-se mais eficiente que as metodologias até então descritas na literatura. Foi aplicado o método GAFIS, em conjunto com um simulador completo para o sistema de refrigeração, Genesym, na otimização de unidades comerciais de condicionamento de ar de alto desempenho. Estudaram-se casos onde o sistema atingiu aumentos de até 15,3 por cento no coeficiente de performance. Em outros estudos, obtiveram-se casos onde o custo de produção foi reduzido em 3,85 por cento (do custo total da unidade), mantendo-se um similar desempenho (capacidade e COP). Testes de otimização, considerando-se diferentes diâmetros dos tubos, na construção dos trocadores de calor, e sistemas com distribuição não uniforme de velocidade de ar, também foram realizados com o GAFIS. Igualmente foram estudados condensadores de microcanais, devido ao interesse atual da indústria com estes trocadores de calor. A otimização do circuito para o refrigerante, neste caso, é relativamente simples, devido ao baixo custo computacional das simulações. Entretanto, modelos de simulação adequados para estes tipos de trocadores de calor só recentemente começaram a surgir, e não têm sido explorados de maneira adequada até a presente data. Explorou-se no presente trabalho, a influência, no desempenho térmico do condensador, dos parâmetros que definem o circuito do refrigerante. Para tal efeito, desenvolveu-se um modelo de simulação baseado em análise local, validado com dados experimentais disponíveis, de condensadores de microcanais de uso automotivo com diâmetro hidráulico (lado do refrigerante) de 0,9 e 1,0mm, para refrigerantes R-134a, Fluid-H e R-1234yf. Foram encontradas relações diretas entre os parâmetros geométricos que definem os circuitos de refrigerante no condensador e seu desempenho térmico. Tal fato pode ser utilizado como orientação expedita para o projeto do circuito ótimo do condensador.<br>Refrigerant circuiting in condensers and evaporators has a significant effect in the performance of refrigeration systems. The optimized project of the refrigerant circuits in refrigeration systems with plate-fin heat exchangers is not trivial, due to the complexity of their representation as well as the high number of possible combinations, even when methodologies of intelligent optimization are used. The present work proposes a new methodology for the simultaneous optimization of refrigerant circuiting in air-air refrigeration systems with plate-fin heat exchangers. This new methodology, here defined as GAFIS (Genetic algorithms applied in filtered spaces), has proven to be more efficient than traditional methods. The GAFIS method was applied, in conjunction with a full refrigeration system simulator, Genesym, for the optimization of high performance commercial air-conditioning units. Typical cases were studied and a coefficient of performance improvement of up to 15.3 percent has been observed. In other studies, there were cases where the manufacturer s predicted cost was reduced in 3,85 percent (of total cost of the unit), while a similar thermal performance (capacity and COP) was maintained. Optimization tests, considering different diameters of tube, for the construction of heat exchangers, as well as systems with non-uniform air velocity distribution, were also performed with the GAFIS method. Microchannel condensers were also studied, given the current interest of industry on this kind of heat exchanger. The optimization of the refrigerant circuiting, in this case, would not be a major problem, due to the low computational cost of its simulation. However, simulation models appropriate for these types of heat exchangers have only been recently in use, and, to date, have not been adequately explored. In the present work, the influence on condenser performance of parameters that define the refrigerant circuiting has been investigated. For this purpose, a simulation model, based on local analysis, was developed. It was validated against experimental data, available from automotive microchannel condenser tests, with hydraulic diameters (refrigerantside) of 0.9 and 1.0mm for refrigerants R-134a, Fluid-H and R-1234yf. A direct relation was found between the geometric parameters that define the condenser refrigerant circuiting and its thermal performance. This fact can be appropriately used as guidance for expeditious design practices of the optimal refrigerant circuit of the condenser.

The impact of refrigeration systems on the environment can be reduced by the use of alternative reffigerants which are less harmful to the atmosphere and the optimisation of systems and control strategies to deliver increased levels of energy efficiency. Mathematical modelling offers the opportunity to test the performance of systems under different operating conditions and with alternative refrigerants. Dynamic models allow comparison of both transient and steady-state behaviour and this is of particular importance for liquid chillers, since these systems can operate under transient conditions for long periods. This thesis details the development of a general dynamic model for the simulation of liquid chillers. Mathematical models of the reciprocating compressor, expansion valve, evaporator and condenser are presented. The models are integrated to form the overall system model by passing conditions from one component to another. A series of steady-state and transient experimental tests were carried out on a liquid chiller and the model was used to simulate these tests. Validation was carried out by comparison of these measured results to those predicted by the simulation for both the steady-state and transient tests. Once validated, the model was used to investigate the steady-state and dynamic performance of liquid chillers operating with various refrigerants. The effect of the mass of the system refrigerant charge was examined for a number of refrigerants. The steady-state performance for a range of evaporator and condenser coolant temperatures was also investigated. Finally, the effect of different system refrigerants on start-up transients was examined and the losses in cooling capacity due to cycling quantified. The effect of the expansion valve's initial superheat spring setting on the dynamic response and transient losses was also investigated.

Thesis (Ph. D.) -- University of Maryland, College Park, 2006.<br>Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

The numerical simulation model presented is based on the integration of the fluid conservation equations (continuity, momentum and energy) in the whole compressor domain (compression chamber, valves, manifolds, mufflers, connecting tubes, parallel paths, etc.) using instantaneous local mean values for the different variables. It is interesting to remark how momentum equation has been taken into account in all compressor parts and the possibility to solve parallel paths, resonators, etc. Effective flow areas are evaluated considering multidimensional models based on modal analysis of fluid interaction in the valve. Then, second and third order vibration models of valve are also considered. The possibility to use compound bound has been also implemented.<br/><br/>The force balances in the crankshaft connecting rod mechanical system are simultaneously solved at each time-step considered in the thermal and fluid dynamic compressor model. It allows to evaluate the instantaneous compression chamber volume and the different forces in the crankshaft connecting rod mechanical system. Mechanical system forces allows to know important information to predict possible<br/>over-stresses in piston, piston pin, crankshaft, connecting rod, etc.<br/><br/>The thermal analysis of the solid elements is based on global energy balances at each macro volume considered (shell, muffler, tubes, cylinder head, crankcase, motor, etc.). Some improvements can be implemented (shell conduction, heat transfer coefficient evaluation, etc.).<br/><br/>The resulting governing equations (fluid flow, valve dynamics, conduction heat transfer in solids, etc.) are discretized by means of a fully implicit control volume formulation. The complete set of algebraic equations are coupled using the segregated he complete set of algebraic equations are coupled using the segregated pressure based algorithm Semi-Implicit Method for Pressure-Linked Equations(SIMPLEC) extended to compressible flow. Second and third time order schemes have been implemented for the transient terms.<br/><br/>An extensive hermetic reciprocating compressor experimental validation has been presented and the experimental know-how acquired has been highlighted. Furthermore, two commercial hermetic reciprocating compressor have been instrumented in detail to obtain the thermal temperatures map and the pressure fluid evolutions along compressor for different working conditions. It is interesting to remark as a novelty, the use of very small absolute pressure transducers, instead of the standard relative transducers. They allow to know instantaneous absolute pressure inside compressor chamber, without the necessity of measurement an absolute pressure outside the compression chamber (as is usual in this kind of experimental works). <br/><br/>The global comparative results have allowed to check the possibilities of the numerical simulation presented above and its accuracy compared with experimental data. After that, this work show the capabilities offered by the simulation presented and its final objective, a better understanding of the thermal and fluid dynamic compressor behaviour to improve the design of these equipments.<br/><br/>Then, the objective has been to review and present different physically meaningful parameters that characterize the reciprocating compressor behaviour (volumetric efficiency, isentropic efficiency, heat transfer efficiency, mechanical, electrical and heat losses, Coefficient of Performance, etc.), their influence detachment and evolution under different working conditions, with the idea to predict the performance of hermetic reciprocating compressors under different working conditions using the above mentioned non-dimensional parameters.<br/><br/>Finally, a parametric study of hermetic reciprocating compressors behaviour has been carried out. Results presented show the influence of different aspects (geometry, valves, motor, working conditions, etc.) in the compressor behaviour. <br/><br/>The parametric studies and compressor characterization detachment allows also a better implementation of simplest models of the compressors in the thermal and fluid dynamic numerical simulation of vapour compressor cycles together with the rest of elements.

The aim of this work is to study the thermal and fluid-dynamic behavior of vapor compression refrigerating systems and their constitutive elements (heat exchangers, expansion devices, compressors and connecting tubes) focused on the use of natural refrigerants (carbon dioxide, isobutane and ammonia). The specific topics analyzed throughout this thesis have arisen from the growing interest in environmentally friendly refrigerants that has led the CTTC group (Centro Tecnológico de Transferencia de Calor) to undertake significant research efforts and to take part in several projects with national and European institutions. The information reported herein represents a summary of the work carried out by the author during the last years together with the contributions provided by other members of the CTTC group. This thesis has led to the creation of some publications in International Conferences and indexed journals. The main achievement of this work has been the development of a flexible numerical tool based on several subroutines. The whole numerical infrastructure is the result of coupling the specific resolution procedures for each vapor compression refrigerating system component together with the whole system resolution algorithm. The simulations have been oriented to study the system thermodynamical characteristics as well as some relevant aspects of its particular elements. In addition to the numerical results a significant experimental work has also been carried out in the CTTC facilities due to the need for experimental validation. The author has been fully involved in data acquisition procedures and has also collaborated in the setting up of the experimental units. In general, all the studies conducted in this work have been presented following the same structure: i) numerical model and resolution procedure explanation; ii) model validation against experimental data; and iii) simulation results. The specific topics tackled within this thesis include the implementation of a two-phase numerical model to simulate the thermal and fluid-dynamic behavior of single- and two-phase flows inside ducts, the study of heat transfer coefficient empirical correlations for both cooling of carbon dioxide at transcritical conditions and evaporation of ammonia at overfeed conditions, the implementation of a numerical model to simulate capillary tubes in order to study their behavior at typical operational conditions found in household refrigerators working with isobutane, the development of a two-phase flow distribution model to simulate heat exchangers made up by manifold systems, and the study of vapor compression refrigeration cycles with special emphasis on carbon dioxide transcritical situations. The set of the numerical models implemented has demonstrated to be a flexible tool as several different aspects of refrigeration vapor compression systems have been successfully simulated and study. It has also demonstrated to be an accurate tool as the numerical results achieved have shown good agreement against experimental data<br>The aim of this work is to study the thermal and fluid-dynamic behavior of vapor compression refrigerating systems and their constitutive elements (heat exchangers, expansion devices, compressors and connecting tubes) focused on the use of natural refrigerants (carbon dioxide, isobutane and ammonia). The specific topics analyzed throughout this thesis have arisen from the growing interest in environmentally friendly refrigerants that has led the CTTC group (Centro Tecnológico de Transferencia de Calor) to undertake significant research efforts and to take part in several projects with national and European institutions. The information reported herein represents a summary of the work carried out by the author during the last years together with the contributions provided by other members of the CTTC group. This thesis has led to the creation of some publications in International Conferences and indexed journals. The main achievement of this work has been the development of a flexible numerical tool based on several subroutines. The whole numerical infrastructure is the result of coupling the specific resolution procedures for each vapor compression refrigerating system component together with the whole system resolution algorithm. The simulations have been oriented to study the system thermodynamical characteristics as well as some relevant aspects of its particular elements. In addition to the numerical results a significant experimental work has also been carried out in the CTTC facilities due to the need for experimental validation. The author has been fully involved in data acquisition procedures and has also collaborated in the setting up of the experimental units. In general, all the studies conducted in this work have been presented following the same structure: i) numerical model and resolution procedure explanation; ii) model validation against experimental data; and iii) simulation results. The specific topics tackled within this thesis include the implementation of a two-phase numerical model to simulate the thermal and fluid-dynamic behavior of single- and two-phase flows inside ducts, the study of heat transfer coefficient empirical correlations for both cooling of carbon dioxide at transcritical conditions and evaporation of ammonia at overfeed conditions, the implementation of a numerical model to simulate capillary tubes in order to study their behavior at typical operational conditions found in household refrigerators working with isobutane, the development of a two-phase flow distribution model to simulate heat exchangers made up by manifold systems, and the study of vapor compression refrigeration cycles with special emphasis on carbon dioxide transcritical situations. The set of the numerical models implemented has demonstrated to be a flexible tool as several different aspects of refrigeration vapor compression systems have been successfully simulated and study. It has also demonstrated to be an accurate tool as the numerical results achieved have shown good agreement against experimental data

The aim of this work is to study the thermal behavior and fluid-dynamic systems, vapor compression refrigeration and its components (heat exchangers, expansion devices, compressors, connecting pipes, pumps and pressure vessels). Topics discussed throughout this thesis arise from the growing interest in refrigerants friendly environment as well as different types of cooling systems for vapor compression has motivated the research group of the CTTC (Centre for Heat Transfer Technology ) to carry out major research efforts as well as participate in several projects with national and European institutions. The information contained in this thesis represents a summary of work performed by the author in recent years but also includes many of the contributions made by other members of CTTC. This thesis has led to the publication of several articles in international conferences. The main achievement of this thesis was the development of a numerical tool based on several subroutines flexibility to study different cooling Systemas vapor compression. The entire digital infrastructure has been the result of attaching specific numerical resolutions of each element of the cycle with the overall resolution algorithm. The simulations have been oriented to the study of thermodynamic cycle as well as to study some relevant aspects of the elements. In addition to the numerical results has been carried out important experimental work in the CTTC facilities in order to validate numerical models. The author has been fully involved in the process of data acquisition and has collaborated in the development of the units. The thesis is structured into five chapters plus a final conclusions and future actions. The first chapter, the introduction puts the reader in regard to the problematic situation, the history of cooling and objectives. The second presents the mathematical formulation and numerical methodology used in the simulation of the different elements and all cooling systems. The third study presents the numerical code verification. The fourth focuses on the validation of models with experimental results. And finally the fifth presents a suite of parametric studies and analysis. The numerical simulation code implemented has proven to be a flexible tool as various aspects of the steam compression systems have been successfully simulated and studied. It has also proven a reliable and good level of accuracy as the numerical results have been simulated properly the various experimental data compared.

[EN] Climate change is one of the short term threats for the humanity because it can affect seriously to the environment and, consequently, to vegetal and animal life. If it is not stopped in next years, maybe this effect will be irreversible. Climate change is produced by anthropogenic emissions of Greenhouse Gas to Earth's atmosphere. Vapour compression systems are one of the main contributors to this phenomenon. Among them, commercial refrigeration applications, through HFC usage, can be highlighted. Since 1990s, developed countries supermarkets are using refrigerants (mainly R134a, R404A and R507A) with great impact (high GWP values) on the climate change due to leakages, especially from parallel compressor rack DX systems. Recently, some regulations and directives have been approved to limit GWP values of HFC used in most extended refrigeration and air conditioning applications, directly affecting to commercial refrigeration. In this thesis, some low-GWP alternatives to replace the most commonly used HFC refrigerants in commercial refrigeration are evaluated, taking into account the limitations imposed by these regulations. To carry out this evaluation, the current status of parallel compressor rack refrigeration systems and their fluids has been reviewed. Then, the different low-GWP options to replace R134a and R404A have been studied. HFOs and their mixtures with HFC have been highlighted as the most promising drop-in or retrofit alternatives. Thus, R1234yf, R1234ze(E) and R450A were proposed to replace R134a and R448A to substitute R404A. The theoretical performance of the different low-GWP alternative fluids, as an overview of their potential use, has been studied at typical parallel compressor rack refrigeration operating conditions using the basic thermodynamic vapour compression cycle. Given the good theoretical performance of these refrigerants, they have been tested in a vapour compression test bench. From the experimental results it is depicted that R1234yf and R1234ze(E) are not acceptable as drop-in or light retrofit refrigerants from an energetic point of view. These fluids, when used in R134a systems, require system modifications (more severe in the case of R1234ze(E)) to achieve acceptable energy efficiency values. Moreover, due to the large refrigerant charge in PCRRS, both HFOs could present problems relating to security. Thus, while R450A presents a GWP value of 547, it appears as the best option to replace R134a due to the similar energy efficiency and properties. Its experimental mass flow rate and cooling capacity are slightly lower than R134a, but the final COP is approximately the same. The best R450A results when compared to R134a are obtained at higher CRs. Although can obtain better efficiency results in new systems, with a minor TXV adjustment R448A shows very high performance when it is used in R404A systems. Despite R448A lower cooling capacity than that R404A, this HFC/HFO mixture can achieve great CO2 equivalent emission reductions and it is recommended as lower-GWP replacement for R404A.<br>[ES] El cambio climático es una amenaza para la humanidad ya que puede afectar seriamente al medio ambiente y, en consecuencia, a la vida animal y vegetal. Si en los próximos años no se actúa para detenerlo, tal vez este efecto sea irreversible. Entre otros factores, el incremento de la temperatura global es producido por las emisiones antropogénicas de gases de efecto invernadero a la atmósfera. La refrigeración comercial, basada en sistemas de compresión de vapor, contribuye de forma relevante a este fenómeno a través del uso de fluidos sintéticos como refrigerantes y del consumo de energía eléctrica procedente de combustibles fósiles. Desde la última década del siglo XX, los supermercados de países desarrollados utilizan HFCs como fluidos de trabajo, principalmente R134a, R404A y R507A. Estos gases, de alto potencial de calentamiento atmosférico (PCA), contribuyen al cambio climático al fugarse accidentalmente de los sistemas de refrigeración, destacando las centrales de compresores en paralelo conectadas a sistemas de expansión directa. El valor máximo de PCA de los HFCs utilizados en aplicaciones de refrigeración y aire acondicionado va a ser controlado por normativas comunitarias, afectando directamente a los fluidos usados comúnmente en refrigeración comercial. Esta tesis evalúa diferentes alternativas de bajo PCA para sustituir los refrigerantes HFC más utilizados en refrigeración comercial, teniendo en cuenta las limitaciones impuestas por las normativas actuales. Para llevar a cabo dicho estudio, se revisa el estado actual de los sistemas de centrales de compresores en paralelo y sus fluidos. A continuación, se analizan las diferentes opciones de bajo PCA para sustituir al R134a y R404A. Al destacar los HFOs y sus mezclas con HFCs como alternativas para realizar un reemplazo con pocas modificaciones del sistema (propiedades similares); R1234yf, R1234ze(E) y R450A son propuestos para sustituir al R134a y R448A para R404A. El rendimiento teórico de los diferentes fluidos alternativos de bajo PCA, para obtener una visión general del potencial de su uso, se estudia simulando las condiciones operativas típicas de las centrales de compresores en paralelo, usando el ciclo termodinámico de compresión de vapor básico. Dado el buen rendimiento mostrado por estos refrigerantes, son ensayados en un banco de pruebas de compresión de vapor. De los resultados experimentales se observa que R1234yf y R1234ze(E) no son aceptables desde un punto de vista energético como sustitutivos directos o con menores modificaciones. Dichos fluidos, cuando son utilizados en sistemas de R134a, requieren modificaciones del sistema (más severas en el caso del R1234ze(E)) para alcanzar valores aceptables de eficiencia energética. Por otra parte, debido a la gran carga necesaria en PCRRS, ambos HFOs podrían presentar problemas en cuanto a la seguridad. Así, mientras que el R450A presenta un valor de PCA de 547, aparece como la mejor opción para sustituir al R134a debido a una eficiencia energética y propiedades similares. El caudal másico y la capacidad frigorífica del R450A son ligeramente inferiores en comparación con las del R134a, pero por otra parte, el COP resultante es aproximadamente el mismo. Los mejores resultados obtenidos para R450A son obtenidas a altas tasas de compresión. Aunque puede ser obtenida una eficiencia energética más alta en sistemas de nuevo diseño, con sólo un ajuste menor de la válvula de expansión termostática, el R448A muestra valores muy altos de rendimiento en sistemas utilizados con R404A. A pesar de que la capacidad frigorífica del R448A es menor que la del R404A, esta mezcla de HFC y HFO puede dar lugar a grandes reducciones de emisiones de CO2 equivalentes, siendo así recomendado como reemplazo del R404A con menor PCA.<br>[CAT] El canvi climàtic és una amenaça per a la humanitat ja que pot afectar seriosament el medi ambient i, en conseqüència, la vida animal i vegetal. Si en els propers anys no s'actua per aturar-lo, potser aquest efecte siga irreversible. Entre altres factors, l'increment de la temperatura global és produït per les emissions antropogèniques de gasos d'efecte hivernacle a l'atmosfera. La refrigeració comercial, basada en sistemes de compressió de vapor, contribueix de manera rellevant a aquest fenomen per l'ús de fluids sintètics com refrigerants i pel consum d'energia elèctrica procedent de combustibles fòssils. Des de l'última dècada del segle XX, els supermercats dels països desenvolupats utilitzen HFCs com fluids de treball, principalment R134a, R404A i R507A. Aquests gasos, d'alt potencial d'escalfament atmosfèric (PCA en castellà), contribueixen al canvi climàtic quan s'escapen accidentalment dels sistemes de refrigeració. D'aquest tipus de sistemes destaquen com a grans emissors de diòxid de carboni les centrals de compressors en paral·lel connectades a sistemes d'expansió directa. El valor màxim de PCA dels HFCs utilitzats en aplicacions de refrigeració i aire condicionat serà controlat per normatives comunitàries, cosa que afectarà directament els fluids utilitzats a la gran majoria de sistemes de refrigeració comercial. Aquesta tesi avalua diferents alternatives de baix PCA per substituir els refrigerants HFC més utilitzats en refrigeració comercial sense oblidar les limitacions imposades per les normatives actuals. Per dur a terme aquest estudi, es revisa l'estat actual dels sistemes de centrals de compressors en paral·lel i els seus fluids. A continuació, s'analitzen les diferents opcions de baix PCA per substituir l'R134a i l'R404A. Els HFOs i les seves mescles amb HFCs com alternatives destaquen per permetre una substitució amb poques modificacions del sistema (propietats similars); R1234yf, R1234ze(E) i R450A són proposats per substituir l'R134a i R448A per l'R404A. Per obtenir una visió general del potencial de l'ús dels diferents fluids alternatius de baix PCA, s'estudia el seu rendiment teòric mitjançant una simulació de les condicions operatives típiques de les centrals de compressors en paral·lel. Per a aquesta simulació s'empra el cicle termodinàmic de compressió de vapor bàsic. Com a conseqüència del bon rendiment mostrat per aquests refrigerants, són assajats en un banc de proves de compressió de vapor. Dels resultats experimentals s'observa que R1234yf i R1234ze(E) no són acceptables des d'un punt de vista energètic com a substitutius directes o amb menors modificacions. Aquests fluids, quan són utilitzats en sistemes de R134a, requereixen modificacions del sistema (més severes en el cas de l'R1234ze(E)) per assolir valors acceptables d'eficiència energètica. D'altra banda, a causa de la gran càrrega necessària en PCRRS, tots dos HFOs podrien presentar problemes en temes de seguretat. Així, mentre que el R450A presenta un valor de PCA de 547, apareix com la millor opció per substituir l'R134a a causa de una eficiència energètica i propietats similars. El cabal màssic i la capacitat frigorífica de l'R450A són lleugerament inferiors en comparació amb les de l'R134a, però d'altra banda, el COP resultant és aproximadament el mateix. Els millors resultats de l'R450A són obtinguts a altes taxes de compressió. Tot i que pot ser obtinguda una eficiència energètica més alta en sistemes de nou disseny, amb només un ajust menor de la vàlvula d'expansió termostàtica, l'R448A mostra valors molt alts de rendiment en sistemes utilitzats amb R404A. Encara que la capacitat frigorífica de l'R448A és menor que la de l'R404A, aquesta barreja de HFCs i HFO pot aconseguir grans reduccions d'emissions de CO2 equivalents, i es per tant es recomanada com a reemplaçament amb menor PCA de l'R404A.<br>Mota Babiloni, A. (2016). ANALYSIS OF LOW GLOBAL WARMING POTENTIAL FLUORIDE WORKING FLUIDS IN VAPOUR COMPRESSION SYSTEMS. EXPERIMENTAL EVALUATION OF COMMERCIAL REFRIGERATION ALTERNATIVES [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/62680<br>TESIS<br>Premiado

Se ha desarrollado y construido una infraestructura experimental orientada a la validación de modelos de intercambiadores compactos de aletas y tubos y sistemas de refrigeración con sobrealimentación de líquido. El objetivo ha sido la obtención de datos experimentales fiables, con condiciones geométricas y de contorno exactamente definidas, para poder compararlos inequívocamente con resultados de simulaciones numéricas. <br/><br/>Se presentan los modelos matemáticos, objetivo de la validación, y una descripción detallada del circuito de aire, del refrigerante líquido, y del refrigerante de cambio de fase, que integran la infraestructura.<br/><br/>Estos tres circuitos están encargados de asegurar condiciones estables y controladas para los prototipos ensayados y para el sistema de refrigeración con sobrealimentación de líquido, en un amplio rango de temperaturas, flujos másicos y potencias. <br/><br/>El diseño permite el ensayo de prototipos de intercambiadores de calor con diferentes geometrías y dimensiones. <br/><br/>Se presentan detalladamente los instrumentos de medida con sus precisiones, montaje, se describen también los componentes y los parámetros de la unidad de adquisición de datos.<br/><br/>Especial atención se ha dedicado a la calibración de los instrumentos de medida como parte esencial del proceso de preparación de los ensayos. Se describe el proceso de estimación de las incertidumbres sistemáticas de los sensores calibrados. Se expone en detalle la formulación y la metodología adoptada para el análisis de incertidumbre de los resultados experimentales.<br/><br/>El procesamiento y el análisis de los datos experimentales se ha realizado en forma automática con un código computacional especialmente desarrollado, encargado de calcular los resultados a partir de las variablas medidas, de llevar a cabo el análisis de incertidumbres detallado, y de comparar los resultados numéricos y experimentales.<br/><br/>Se presentan resultados experimentales obtenidos con la infraestructura experimental desarrollada. Se presentan estudios detallados de intercambiadores de calor compactos en condiciones de enfriamiento de aire, utilizando refrigerante líquido y de cambio de fase. Se presentan también resultados del estudio experimental del sistema de refrigeración con sobrealimentación de líquido. Los resultados han sido comprobados y verificados a través de balances energéticos en todos los componentes, donde la misma magnitud física ha sido evaluada de mediciones independientes. Con el objetivo de permitir el uso mas general de los resultados experimentales se presentan también los datos crudos de las variables medidas durante los ensayos.<br/><br/>Se ha propuesto una metodología de validación para el modelo de intercambiadores compactos, basada en comparaciones sistemáticas de resultados numéricos y experimentales. Estas comparaciones han sido analizadas en términos estadísticos con el objetivo de cuantificar las diferencias observadas y dar una evaluación global de las prestaciones del modelo numérico en las condiciones ensayadas. La metodología propuesta para la validación del modelo de intercambiadores compactos puede ser utilizada como base para metodologías de validación en general.<br>Experimental infrastructures intended for validation of compact heat exchanger models, and models of liquid overfeed refrigeration systems have been developed and constructed. The aim has been the obtaining of reliable experimental data from tests at exactly defined geometrical and boundary conditions, permitting the unequivocal comparisons with numerical simulation results. <br/><br/>The mathematical models are presented and detailed description of the airhandling, the liquid refrigerant, and phase-changing refrigerant circuits integrating the experimental infrastructure is given.<br/><br/>These three circuits are encharged to provide stable controlled conditions for the tested prototypes and the liquid overfeed system in the desired range of temperatures, fluid flows, and capacities. <br/><br/>The design permits the accommodation of heat exchanger prototypes with different geometry and sizes.<br/><br/>Detailed overview of the measuring instruments is presented, with their accuracies and mounting, and the components and parameters of the data acquisition system are described.<br/><br/>Special attention has been paid to the calibration of the measuring instruments as an essential part of the test preparation. The process of estimation of the systematic uncertainties in the calibrated sensors measurements is described. The formulation and the methodology adopted for the uncertainty analysis of the experimental results is exposed in detail.<br/><br/>The experimental data processing and analysis has been performed automatically with a specially developed program encharged with the calculation of the experimental results from the measured variables, the detailed uncertainty analysis, and the numerical to experimental results comparisons.<br/><br/>Experimental results obtained with the developed infrastructure are presented. Detailed studies of compact heat exchangers under cooling conditions, using liquid and phase-changing refrigerants, are performed and presented. Results from the experimental studies of the liquid overfeed refrigeration system are also presented. The results have been checked and verified through energy balance checks for all the components where measurements of the same physical magnitude can be contrasted with independent measurements. In order to give more general use of the obtained experimental data, the raw measured variables during the tests are also presented.<br/><br/>An experimental validation methodology for the compact heat exchanger model has been proposed, based on systematic comparisons between numerical and experimental results. The comparisons have been analysed in statistical terms in order to quantify the observed differences and to give global evaluation of the numerical model performance in the tested conditions. The methodology proposed for validation of the heat exchanger model can be used as a basis for validation methodology for numerical models in general.

A presente se tese desenvolve uma metodologia para comparar as substâncias emitidas na construção e operação de sistema frigorífico por absorção e por compressão de vapor de amônia usando a metodologia denominada Análise do Ciclo de Vida (ACV). Pesquisas bibliográficas feitas pelo autor desse trabalho permitem a conclusão de haver poucas informações que permitam a elaboração de um inventário de ciclo de vida para ciclo frigorífico por absorção e por compressão de vapor tendo como fluido de trabalho a amônia. Realizado todo o dimensionamento termodinâmico e mecânico dos ciclos e aplicada a metodologia ACV, os resultados demonstram que a operação do ciclo frigorífico por compressão produz 626,91% mais de hidrocarbonetos quando comparada com a quantidade emitida devido a construção. Demonstram ainda que as substâncias emitidas são diferentes para o ciclo por absorção e para o por compressão de vapor de amônia.<br>This thesis proposes to develop a way to compare the substances emitted in the construction and operation of a refrigeration cycle by absorption and compression of vapor ammonia using the methodology called Life Cycle Analysis (ACV). Bibliographic researches made by the author of this study suggest there is little information to allow the construction of an inventory of the life cycle to a refrigeration systems. Carried out all the thermodynamic and mechanical design cycles and applied the ACV methodology, the results demonstrate that the operation of the compression cycle produce 626,91% more hydrocarbon in comparison with the construction. The results shows that the substances emitted by absorption or compression cycle are different.

Orientador: Luiz Felipe Mendes de Moura<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica<br>Made available in DSpace on 2018-08-12T21:08:34Z (GMT). No. of bitstreams: 1 Brandao_MatheusMarcelino_M.pdf: 452664 bytes, checksum: 124f6ab109716c77cffe6f192c006b30 (MD5) Previous issue date: 2005<br>Resumo: No presente trabalho se realiza o estudo e desenvolvimento de um modelo numérico computacional com a finalidade da simulação de sistemas de refrigeração por compressão de vapor. Em um primeiro momento, foram analisados e discutidos os principais tipos de modelamento para cada componente do sistema de refrigeração (compressor, condensador, válvula de expansão e evaporador) encontrados na literatura. Após esta primeira análise, foram escolhidos os modelos utilizados para o desenvolvimento do programa computacional. O programa foi validado a partir da comparação dos resultados obtidos numericamente com os obtidos em ensaios experimentais. Após a validação, foram feitos dois estudos de casos, para a verificação da influência dos parâmetros sobre os sistemas simulados e otimização do desempenho de tais sistemas<br>Abstract: This work performs the study and development of a numerical computational model in order to simulate refrigeration systems by steam compression. At first, the main types of modelation for each component of the refrigeration system (compressor, condenser, expansion valve and evaporator) found in literature are analysed and discussed. After this first analysis, the models for the development of a computational program are chosen. The program is validated by means of the comparison of the results obtained numerically with those acquired in experimental tests. Just after validation, two studies of cases are made to verify the influence of the parameters on the simulated systems and to optimize the performance of those systems<br>Mestrado<br>Termica e Fluidos<br>Mestre em Engenharia Mecânica

Розділ 1 "Спеціальний розділ": розрахунок ротаційно-пластинчастого компресора, розрахунок поршневого компресора, розрахунок гвинтового компресора, розрахунок спірального компресора, порівняльний аналіз різних типів компресорів, визначення витрати газу через зазори спірального компресора; розділ 2 «Охорона праці та безпека у надзвичайних ситуаціях»: небезпечні і шкідливі фактори компресорного виробництва, розрахунок захисного заземлення електроприводу, розрахунок хімічної обстановки на об'єкті у зв’язку з аварією на прилеглій залізничній станції, що призвела до руйнування ємності з аміаком; розділ 3 «Економічний розділ»: розрахунок собівартості і проекту оптової ціни проектованого компресора, розрахунок капітальних витрат споживача, розрахунок експлуатаційних витрат споживача, розрахунок показників економічної ефективності нової техніки, порівняльний аналіз цін компресорів при однаковій холодопродуктивності.<br>Раздел 1 "Специальный раздел": расчет ротационно-пластинчатого компрессора, расчет поршневого компрессора, расчет винтового компрессора, расчет спирального компрессора, сравнительный анализ различных типов компрессоров, определения расхода газа через зазоры спирального компрессора; раздел 2 «Охрана труда и безопасность в чрезвычайных ситуациях»: опасные и вредные факторы компрессорного производства, расчет защитного заземления электропривода, расчет химической обстановки на объекте в связи с аварией на прилегающей железнодорожной станции, привела к разрушению емкости с аммиаком; раздел 3 «Экономический раздел»: расчет себестоимости и проект оптовой цены проектируемого компрессора, расчет капитальных затрат потребителя, расчет эксплуатационных расходов потребителя, расчет показателей экономической эффективности новой техники, сравнительный анализ цен компрессоров при одинаковой холодопроизводительности.<br>Section 1 "Special Section": calculation of a rotary vane compressor, calculation of a piston compressor, calculation of a screw compressor, calculation of a scroll compressor, comparative analysis of various types of compressors, determination of gas flow through the gaps of a scroll compressor; Section 2 “Labor protection and safety in emergency situations”: dangerous and harmful factors of compressor production, calculation of protective grounding of the electric drive, calculation of the chemical situation at the facility in connection with an accident at an adjacent railway station, led to the destruction of the tank with ammonia; Section 3 “Economic section”: calculation of the cost and draft of the wholesale price of the designed compressor, calculation of consumer capital costs, calculation of consumer operating costs, calculation of indicators of economic efficiency of new equipment, comparative analysis of compressor prices with the same cooling capacity.

Systematické řízení tepelných a elektrických toků v plně elektrických automobilech se stává velmi důležitým, protože v těchto typech automobilů není k dispozici dostatek odpadního tepla pro vytápění kabiny. Aby v zimním období nedocházelo ke snížení dojezdu, je nutné použití technologií, které umožní snížení spotřeby energie nutné k vytápění kabiny (např. tepelné čerpadlo, zásobník tepla). Je také zapotřebí vytvořit řídicí algoritmy pro tato zařízení, aby byl zajištěn jejich optimální provoz. V letním období je nezbytné řídit tepelné toky v rámci elektromobilu tak, aby nedocházelo k nadměrnému vybíjení baterie kvůli chlazení kabiny a dalších částí. Tato práce řeší jak návrh řídicích algoritmů, tak i vývoj rozhodovacího algoritmu, který zajistí směřování tepelných toků.

Made available in DSpace on 2014-06-11T19:22:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-09-25Bitstream added on 2014-06-13T19:26:47Z : No. of bitstreams: 1 leandro_e_me_ilha.pdf: 1745578 bytes, checksum: 2db70f1465f9f7258fdbcda3cdebf72c (MD5)<br>Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>Este trabalho apresenta uma nova proposta para sistema de refrigeração com controle dinâmico de temperatura, operando com estrutura de compressor aberto, acionado por motor de indução trifásico com velocidade variável, e estágio de entrada retificador com correção ativa do fator de potência. O estágio de entrada é composto por um retificador Boost monofásico com elevado fator de potência, com duas células entrelaçadas, operando no modo de condução crítica, empregando técnica de comutação não dissipativa e controlado por dispositivo FPGA, associado a um estágio de saída inversor de dois níveis convencional trifásico à IGBT, o qual é controlado por um Processador Digital de Sinais (DSP - Digital Signal Processor). A técnica de comutação não dissipativa para o estágio de entrada é baseada em células ZCS (Zero-current-switching). As principais características do retificador incluem a redução da ondulação da corrente de entrada, redução da ondulação da tensão de saída retificada, utilização de componentes com reduzidos esforços, reduzido volume do filtro de entrada para Interferências Eletromagnéticas (EMI - Electromagnetic Interference), elevado Fator de Potência (FP) e reduzida Distorção Harmônica Total (DHT) da corrente de entrada, atendendo os limites da norma IEC61000-3-2. O controle digital para o estágio de saída inversor foi desenvolvido usando duas diferentes técnicas, incluindo a técnica convencional controle escalar Volts/Hertz (V/Hz) e o controle Vetorial com Orientação pelo Fluxo do estator, com o propósito de verificar a aplicabilidade e a performance dos controles digitais propostos, para o controle contínuo da temperatura, aplicados a um protótipo de sistema de refrigeração.<br>This work presents a new proposal for refrigeration systems with dynamic control of temperature, working with structure of open compressor, driving a three-phase induction motor with variable speed, and input rectifier with active power factor correction. The proposed system is composed of a single-phase high-power-factor boost rectifier, with two cells in interleaved connection, operating in critical conduction mode, and employing a softswitching technique, controlled by a Field Programmable Gate Array (FPGA), associated with a conventional three-phase IGBT bridge inverter (VSI - Voltage Source Inverter), controlled by a Digital Signal Processor (DSP). The soft-switching technique for the input stage is based on zero-current-switching (ZCS) cells. The rectifier s features include reduction in input current ripple, reduction in output voltage ripple, use of low stress devices, low volume for the EMI input filter, high input power factor (PF), and low total harmonic distortion (THD) in the input current, in compliance with the IEC61000-3-2 standards. The digital controller for the output stage inverter has been developed using two different techniques, the conventional Voltage-Frequency control (scalar V/Hz control), and a simplified stator oriented vector control, in order to verify the feasibility and performance of the proposed digital controls, for continuous temperature control, applied at a refrigerator prototype.

Resumo: Este trabalho apresenta uma nova proposta para sistema de refrigeração com controle dinâmico de temperatura, operando com estrutura de compressor aberto, acionado por motor de indução trifásico com velocidade variável, e estágio de entrada retificador com correção ativa do fator de potência. O estágio de entrada é composto por um retificador Boost monofásico com elevado fator de potência, com duas células entrelaçadas, operando no modo de condução crítica, empregando técnica de comutação não dissipativa e controlado por dispositivo FPGA, associado a um estágio de saída inversor de dois níveis convencional trifásico à IGBT, o qual é controlado por um Processador Digital de Sinais (DSP - Digital Signal Processor). A técnica de comutação não dissipativa para o estágio de entrada é baseada em células ZCS (Zero-current-switching). As principais características do retificador incluem a redução da ondulação da corrente de entrada, redução da ondulação da tensão de saída retificada, utilização de componentes com reduzidos esforços, reduzido volume do filtro de entrada para Interferências Eletromagnéticas (EMI - Electromagnetic Interference), elevado Fator de Potência (FP) e reduzida Distorção Harmônica Total (DHT) da corrente de entrada, atendendo os limites da norma IEC61000-3-2. O controle digital para o estágio de saída inversor foi desenvolvido usando duas diferentes técnicas, incluindo a técnica convencional controle escalar Volts/Hertz (V/Hz) e o controle Vetorial com Orientação pelo Fluxo do estator, com o propósito de verificar a aplicabilidade e a performance dos controles digitais propostos, para o controle contínuo da temperatura, aplicados a um protótipo de sistema de refrigeração.<br>Abstract: This work presents a new proposal for refrigeration systems with dynamic control of temperature, working with structure of open compressor, driving a three-phase induction motor with variable speed, and input rectifier with active power factor correction. The proposed system is composed of a single-phase high-power-factor boost rectifier, with two cells in interleaved connection, operating in critical conduction mode, and employing a softswitching technique, controlled by a Field Programmable Gate Array (FPGA), associated with a conventional three-phase IGBT bridge inverter (VSI - Voltage Source Inverter), controlled by a Digital Signal Processor (DSP). The soft-switching technique for the input stage is based on zero-current-switching (ZCS) cells. The rectifier’s features include reduction in input current ripple, reduction in output voltage ripple, use of low stress devices, low volume for the EMI input filter, high input power factor (PF), and low total harmonic distortion (THD) in the input current, in compliance with the IEC61000-3-2 standards. The digital controller for the output stage inverter has been developed using two different techniques, the conventional Voltage-Frequency control (scalar V/Hz control), and a simplified stator oriented vector control, in order to verify the feasibility and performance of the proposed digital controls, for continuous temperature control, applied at a refrigerator prototype.<br>Orientador: Carlos Alberto Canesin<br>Coorientador: Flávio Alessandro Serrão Gonçalves<br>Banca: Fabio Toshiaki Wakabayashi<br>Banca: João Onofre Pereira Pinto<br>Mestre

碩士<br>國立臺灣大學<br>化學工程學研究所<br>101<br>This research aims to develop a mathematical model for handling the design problem of a compression refrigeration system. A superstructure is firstly proposed which can be used to describe all possible configurations of a compression refrigeration system. By describing relevant constrains for each part of the superstructure, and adapting total compressor work or total annual cost as the objective function, the problem of designing the compression refrigeration system can be formulated as a mixed-integer nonlinear program (MINLP) that can then be solved ot determine the optimal configurations and operating conditions. Three numerical examples are presented, with simple or multiple refrigeration loads, in this work in order to demonstrate that the proposed superstructure-based MINLP formulation can be used to decide the suitable configuration of a compression refrigeration system.

碩士<br>臺灣大學<br>化學工程學研究所<br>98<br>This work aims to develop a mathematical model for the synthesis of refrigeration systems with continuous temperature based on a superstructure. The newly proposed model includes all possible configurations of a compression refrigeration system under all conditions. By setting relevant constraints up for each part of the superstructure, the design problem of compression refrigeration system is formulated as a mixed-integer nonlinear program that can be solved for optimal configuration and operating conditions. In this work, two objective functions are considered which involve the minimization of compressor work and total annual cost. With given cooling load and desired temperature, the optimal configuration and operating condition are determined and compared with previous works. Through case studies (or examples), it is shown that the optimal design of compression refrigeration system can be obtained with the proposed model.

碩士<br>國立臺灣大學<br>機械工程學研究所<br>96<br>This research apply Micro-channel Evaporator to Vapor Compression Refriger- ation System (VCRS) for electrical Cooling. Steady and transient States experimental investigations are conducted to analysis the thermal properties depends on the design experimental factor.The cooling capacity of the VCRS varied from 250W to 400W, with COP from 1.7 to 3, at pressure ratios of 1.6 to 2.8.The highest overall second-law efficiency was 70%. In steady state experiment. Micro-channel evaporator efficiently make the heat exchange between CPU base and the evaporator, improving the coefficient of perfor- mance .Because of the icreacing heat load ,too much gass R-134a decreased the heat transfer coefficient.This research discussed the mechanism of the two phase flow in high-heat-flux micro-channel ,using evaporator thermal resistance model in order to predict and control the CPU temperature. In transient experiment.Transient evaporator temperature can control R-134a quality and mass flow rate .A complete experimental and numerical medole was built and tested in order to find out optimimal control of the CPU temperature.

The demands facing the refrigeration industry are minimal usage of conventional energy sources for compression and avoidance of ozone depleting substances. One of the approaches to combat these issues is the use of thermally driven solid sorption compression with non-ozone depleting refrigerant. In this context, the research work presented in this thesis is devoted to a comprehensive thermodynamic analysis and development of a laboratory model of an activated carbon+ HFC 134a adsorption refrigeration system. The cooling load catered to by the laboratory model is 2-5 W, mainly for thermal management of electronics. A complete thermodynamic analysis is carried out for the desorption temperatures varying from 75 to 90 oC, evaporating temperatures from -20 to 15oC and adsorption/condensing temperatures from 25 to 40 oC. A program on MatLab platform is developed for theoretical modeling. A new concept of thermal compression uptake efficiency (u) which is analogous to volumetric efficiency of a positive displacement compressor is introduced to consider the effect of void volume. The thesis also covers an investigation of two-stage and hybrid (thermal+ mechanical) cycle compression systems. It is possible to identify the conditions under which a two-stage gives a better performance than a single-stage one. It also shows that hybrid cycle system gives the best performance and saves ~40% of power compared to operation under the same conditions run with a single-stage mechanical compression refrigeration system. A heat transfer analysis of the thermal compressor is carried out to evaluate non-uniformities in bed temperature. As a part of it, the thermal conductivity of the bed under adsorbed state has been calculated. A laboratory model of activated carbon+ HFC 134a adsorption refrigeration system is fabricated to meet a 2-5 Watts cooling load based on the results from theoretical calculations. Experimental results show a fair match in the trends for the COP with analysis. The main aim of the research was to examine how effective the adsorption refrigeration system is in reducing the temperature rise of the heater used to simulate the electronic component. The heater that would have stabilized at 81, 97, 103 and 112 oC without any cooling for heat inputs of 3, 4, 4.4 and 4.9 W, respectively, would attain a cyclic steady state around 24, 26, 28, 31 oC. The influence of cycle time on the performance of the systems is also investigated. It is concluded that an activated carbon+ HFC 134a adsorption refrigeration system can be a good supplement to conventional compression refrigeration systems. In situations where heat recovery imminent this system could be a good choice. For waste heat recovery and suppression of infrared signatures of electronic components, it is ideally suited where COP becomes immaterial.

The demands facing the refrigeration industry are minimal usage of conventional energy sources for compression and avoidance of ozone depleting substances. One of the approaches to combat these issues is the use of thermally driven solid sorption compression with non-ozone depleting refrigerant. In this context, the research work presented in this thesis is devoted to a comprehensive thermodynamic analysis and development of a laboratory model of an activated carbon+ HFC 134a adsorption refrigeration system. The cooling load catered to by the laboratory model is 2-5 W, mainly for thermal management of electronics. A complete thermodynamic analysis is carried out for the desorption temperatures varying from 75 to 90 oC, evaporating temperatures from -20 to 15oC and adsorption/condensing temperatures from 25 to 40 oC. A program on MatLab platform is developed for theoretical modeling. A new concept of thermal compression uptake efficiency (u) which is analogous to volumetric efficiency of a positive displacement compressor is introduced to consider the effect of void volume. The thesis also covers an investigation of two-stage and hybrid (thermal+ mechanical) cycle compression systems. It is possible to identify the conditions under which a two-stage gives a better performance than a single-stage one. It also shows that hybrid cycle system gives the best performance and saves ~40% of power compared to operation under the same conditions run with a single-stage mechanical compression refrigeration system. A heat transfer analysis of the thermal compressor is carried out to evaluate non-uniformities in bed temperature. As a part of it, the thermal conductivity of the bed under adsorbed state has been calculated. A laboratory model of activated carbon+ HFC 134a adsorption refrigeration system is fabricated to meet a 2-5 Watts cooling load based on the results from theoretical calculations. Experimental results show a fair match in the trends for the COP with analysis. The main aim of the research was to examine how effective the adsorption refrigeration system is in reducing the temperature rise of the heater used to simulate the electronic component. The heater that would have stabilized at 81, 97, 103 and 112 oC without any cooling for heat inputs of 3, 4, 4.4 and 4.9 W, respectively, would attain a cyclic steady state around 24, 26, 28, 31 oC. The influence of cycle time on the performance of the systems is also investigated. It is concluded that an activated carbon+ HFC 134a adsorption refrigeration system can be a good supplement to conventional compression refrigeration systems. In situations where heat recovery imminent this system could be a good choice. For waste heat recovery and suppression of infrared signatures of electronic components, it is ideally suited where COP becomes immaterial.

碩士<br>國立臺灣大學<br>機械工程學研究所<br>97<br>Vapor compression refrigeration system (VCRS) is a cooling system that has high COP and high cooling capacity. The research emphasizes on the characteristics of a miniature VCRS and how the experimental factors affect it. This research can be divided into two parts: steady state experiments and VCRS simulations. In steady state experiments, a VCRS has been designed and assembled. The whole system is about 6 kg weight, and the size of the system is about 160×350×150 mm3. Experimental investigations are conducted to analyze that how the orifice of the expansion valve, heating watt and the rotational speed of the compressor affect the system performances. The results show that the system has a maximum cooling capacity 150W, and the COP of the system varies from 1.36 to 4.25. In VCRS simulation, a program is written to analyze and predict its performances. The program is used to analyze that how the size of the condenser and the evaporator influences the system performances. The errors of the simulations are less than 10%.

碩士<br>國立臺灣師範大學<br>工業教育研究所<br>89<br>Abstract This subject is the study of the relationship between subcooling of liquid refrigerant and promotion of performance of refrigerator. For this purpose, the effects of subcooling temperature on the parameters of the system were discussed firstly in this subject, and then the effects on parameters and consumption of electric power were analyzed. Furthermore, an operational model was proposed to solve the problem of energy consuming according to the result of the analysis. The mainly discoveries and conclusions in this context are as follows. First, from the analysis of correlation, there are great effects of subcooling on the temperature of the evaporator, the refrigerant of condenser and compressor. Furthermore, it do not only increase the difference in enthalpy of the liquid pipe to promote COP, but also quite affects other systematic factors, which is worth being studied by the following researchers. Second, as to the coefficient of the totally systematic performance, COPtotal, it was found that there was the best COPtotal at 2℃ of temperature of the liquid line under this experimental condition but COPtotal decreased for the lower subcooling temperature by utilizing regression equations to extend the range of subcooling temperature. Third, as to the consuming electric power of the total system, KWtotal, there was the lowest KWtotal at 15℃ of temperature of the liquid line but KWtotal increased for the lower subcooling temperature. Therefore, it was found that the COP of this system could be promoted actually within the range of subcooling temperature in this experiment, and thus the correlation between theory and practice was proved, so some suggestions based on the results of this study could be references for the following researchers. Key words: subcooling, coefficient of performance, capillary tube, analysis of correlation, regression equation

This work comprises energetic and exergetic analysis of two thermodynamic cycles: First one is a conventional two stage cooling system by steam compression of ammonia and the other is named integrated refrigeration system. The conventional system that has been used as reference in this work is largely used for cooling purpose in industrial sector. The integrated refrigeration system is similar to the conventional system, but it uses the intermediate cooling, between the stages of high and low pressure, by cold water in closed circuit. The cold water is supplied by LiBr-H2O absorption system integrated to the conventional compression system. The heat input is obtained from waste material. Therefore, the energy supplied to the integrated refrigeration system is assumed of zero cost. Numeric simulation is used to compare the behaviour of both cycles. The results obtained in this comparison show that the integrated refrigeration system operates with a reduction of up to 9.70 % in COP. However, the integrated refrigeration system presented an increase of up to 11.89% in exergetic efficiency and 34.46% in refrigerating capacity in relation to the conventional system. These results, together with decrease in operational cost which will be valuable in further study, will make very attractive the use of the integrated refrigeration system.

碩士<br>國立勤益技術學院<br>冷凍空調系<br>94<br>Over years, the domestic consumption of frozen food has been increasing as the living standard is getting higher and the lifestyle keeps changing. Taiwan, located in sub-tropical area with hot and humid climate, however,has to depend on frozen freezing techniques such as low-temperature logistics, food processing, storage and deep-freezing to maintain the quality and cleanness of frozen food. In industry, these techniques may well be used to atomize and crumble, or to store raw materials, while in agriculture,they are used to keep flowers, fruit, and vegetables fresh. In medical science or biotechnology, these techniques operate well in the preservation of blood, vaccines, and seeds as well as in the pulverization of medicines. Furthermore, with the wider and wider application of the low-temperature system, the demand for the system is getting strict. But, if operated at lower evaporator temperature, the temperature in the one-stage vapor compression refrigeration system meets a certain limit. Thus, to eliminate this defect, the two-stage vapor compression refrigeration system is often adopted. With the development of the refrigeration technology, two-stage vapor compression refrigeration system has been put in practical use in many fields. However, because the two stage system is far more complicated than the one-stage system, the design of its inter-stage pressure becomes crucially important. The variation of outer surroundings willchange the condenser temperature. If the condenser temperature raises, the high stage displacement will decrease, which influences the refrigerant mass flow and consequently, cause the inter-stage pressure to vary at the same time. For this reason, this thesis will give a particular discussion on how the variation of the inter-stage pressure affects the two-stage vapor compression refrigeration system.

碩士<br>國立勤益科技大學<br>冷凍空調系<br>101<br>This research investigate the performance of a two-stage compression refrigeration system using different refrigerants including R-507A,R404A,R-290 and HC-426 HC refrigerant. The experimental analysis of different operation parameter such as charge amount of refrigerants ,cooling capacity, power consum- ption and discharge temperature has been studied extensively under different frequency for high-stage and low-stage compressor respectively. The experiment results reveal the cooling performance of this refrigeration system is the best while operating at the frequency of 50 Hz for high-stage compressor and 70 Hz for low-stage compressor. It also presents higher cooling capacity and lower power consumption for the two-stage refrigeration system .While conducting different refrigerants ,the HC-426 HC refrigerants. The cooling performance is similar other refrigerants. The cooling performance is similar for R-507A ,R-404A and R-290. However , the power consumption of the refrigeration system using R-290 is the lowest while the set point is above -30℃.When the set point is lower than -30℃, the refrigeration system using R-507 or HC-426 HC will be highly recommended.

碩士<br>國立臺北科技大學<br>能源與冷凍空調工程系碩士班<br>98<br>Low-temperature storage refrigeration system is vital for much industry range. The traditional single-stage vapor compressor system is not suitable for low-temperature system; therefore, it should be used cascade refrigeration system. For many years, as a result of environmental protection issue related global warning and depletion of ozone layer caused by the use of synthetic refrigerants (CFC’s, HCFC’s and HFC’s), the return to the use of harmless natural substances as alternative refrigerants in refrigeration systems. Ammonia (R717) and hydrocarbon refrigerant have excellent thermodynamic and thermo-physical properties; they can be used in much range of refrigeration system. In this paper, a cascade refrigeration system with Ammonia (R717) and Hydrocarbon refrigerant (HC) as working fluids in the low and high temperature stages, respectively, has been analysed and compared with R22 and R134a of traditional refrigerant. Further to research and analysis the relation of COP and mass flow ratio versus operating and design parameters of 6 group’s refrigerant in order to get optimization of parameter and analysed refrigerant in cascade low-temperature refrigeration system.

博士<br>國立臺灣大學<br>機械工程學研究所<br>91<br>This dissertation presents studies of a small vapor-compression refrigeration system and wavy channels within plate heat exchangers. In Part I, the performance of a domestic vapor-compression refrigeration system with isobutane (R600a) as the refrigerant was investigated. The input power of the compressor varied between 230 and 300 Watts, while the amount of the charged refrigerant was about 150 grams. The expansion and heat transfer components of the system were capillary tubes and plate heat exchangers (PHE), respectively. The refrigeration temperatures were set at about 4 and -10℃ to simulate the situations of the cold storage and the freezing applications. In the cold storage application, two capillary tubes in parallel gave better performances than a single tube. The proper sizes of the tube are between 4 and 4.5m in length, and 0.7mm in internal diameter in the cold storage application, while in the freezing application they are between 4.5 and 5m in length, and 0.6mm in internal diameter. The COPs of the system lie between 1.2 and 4.5 in the cold storage application and between 0.8 and 3.5 in the freezing application, which are comparable with those of the system with R-12 and R-22 as the refrigerant. In general, the refrigeration capacity increases with the refrigeration loads. In Part II, the heat transfer characteristics of the corrugated channel appeared within PHEs was explored. Five wavy channels with different geometry were constructed within which air was passed through. The channel geometry includes the corrugated angle, the width, the curvature radius of the corrugation part, and the length of straight section of the channel. The temperature of the wall was maintained constant at 60℃. Starting from the entrance, the air temperatures at about 250-500 locations within two wavelengths were monitored with T-type thermocouples. The Reynolds number of air was varied from 300 to 9000 to cover both the laminar and turbulent flow regimes. Results indicate that the local heat transfer coefficients increase with the width of the channel. Both the average and local Nusselt numbers decrease with the Reynolds number but do not change apparently with the width ratio of the channel .In general, the average Nusselt numbers increase with both the corrugated angle and the ratio of the curvature radius of corrugation to the length of the straight part of the channel. The local Nusselt number decreases with the distance from the entrance, a phenomenon commonly occurs in channel flows. However, the heat transfer is greater at sections near the crest after the entrance region. Different characteristics of heat transfer were observed for the laminar and turbulent flow regimes. Empirical relations for the characteristics of these two regimes were obtained with computational approaches.

Parametric investigation of energy and exergy analysis of multi-evaporators at different temperatures with individual expansion valve and individual compressor using flash chamber and liquid vapour heat exchanger is carried out for R134A, R142B, R152A, R600 and R1234YF as alternative refrigerants. In engineering equation solver, a computational model is developed for these systems, simple multi-evaporator system and improved one system. The present investigation has been done for evaporator-I in the range -120C to -200C, evaporator-II in the range 10C to 40C and condenser in the range 350C to 550C. Performance parameters like exergetic efficiency, the coefficient of performance and exergy destruction ratio are calculated over these ranges and compared for these refrigerants. The performance comparison of the simple multi-evaporator system and improved system for dairy plant application, COP improves by 16.99%, 15.97%, 15.88%, 16.24% and 18.41% for refrigerants R134A, R142B, R152A, R600 and R1234YF respectively in multi-evaporator system with flash chamber and LVHE. Exergy efficiency improves by 16.98%, 15.97%, 15.87%, 16.22% and 18.36% for refrigerants R134A, R142B, R152A, R600 and R1234YF respectively in multi-evaporator system with flash chamber and LVHE. Due to additional components in basic system, flash chamber and LVHE, exergy destruction in multi-evaporator system increases. EDR % increases by 20.37%, 16.84%, 14.74%, 18.66% and 24.92% for refrigerants R134A, R142B, R152A, R600 and R1234YF respectively in multi-evaporator system with flash chamber and LVHE. The corresponding values of input energy consumed for expansion valve, evaporator and compressor are varied between 7% to 18%, 11% to 22% and 18 % to 24 % respectively. From the point of enery-exergy analysis, R142B is best among all five selected refrigerants as total exergy destruction of all components is always less for R142B than that of all others and R142B refrigerant has higher COP and Exergetic efficiency in this modified system. Also, R142B has least EDR in this analysis. Though R142B have highest COP and exergetic efficiency among all refrigerants, it is not recommended due to its GWP 2400, which is highest among all. Second best refrigerant R600 has only GWP 3. Hence it is recommended over R142B in dairy plant application.

In recent years, heat pumps and refrigeration systems are widely used in both residential and industrial applications. The possibility of recovering the large throttling losses by using an expander could give a substantial contribution to the performance improvement. In this thesis, a reciprocating expander developed from a hydraulic motor was numerically and experimentally analyzed. A numerical model was developed to identify the needed small modifications to be made on the expander without change its architecture. Successively, an extensive experimental activity on the modified expander has been carried out to characterize it in detail and evaluate the effective performance. With this aim, a dedicated test rig and a measurement system have been developed. The expander was tested in a R134a heat pump cycle and in a CO2 refrigeration cycles. Despite of the mechanical losses due to the different original application of the machine, the thermodynamic cycles showed very promising results with the adoption of this solution. For this reason, a redesign and manufacturing of the machine was done in order to improve the efficiency in HFC cycles and to decrease the mechanical losses. The new version of the expander was tested in a "hot-gas bypass cycle", which has been designed and manufactured. The aim of this cycle is to obtain high stability and flexibility, and lower size due to the lack of the evaporator. The results showed improvement in both the thermodynamic behavior and mechanical losses. Finally, a 1D thermal conduction model has been developed to study the two-phase expansion with R134a with an improved accuracy.

近年來微型製冷系統有許多應用。例如，電子器件的冷却是研製更快速、更小型和更可靠的芯片的重要課題, 隨著電子芯片功耗的增加，散熱量不断增長，傳統的被動式散熱方法已經過時，新的主動式散熱方法成爲必須。又例如微型個人冷卻系統可用於救火等各種惡劣環境。与其它製冷方法相比，蒸氣壓縮製冷技術是最有潜力的方法。<br>本文闡述了两种微型蒸氣壓縮製冷系統的研製工作：一是電子冷却系统，一是個人热舒适系统。研究主要包括以下幾個方面：<br>1) 微型蒸氣壓縮製冷系統的熱力學分析。對系統在不同工作條件下（包括壓縮機效率、環境溫度等）的性能進行了分析。对換熱器的設計也作了详述。<br>2) 微型蒸氣壓縮製冷系統的熵分析。通過分析發現，壓縮機和系統漏熱造成的熵是產生系統不可逆性的主要因素,因此高效的壓縮機和降低系統漏熱是提高微型蒸氣壓縮製冷系統性能的關鍵所在。<br>3) 實驗系统的詳細介紹。一共做了两套微型蒸氣壓縮製冷系統，一为電子冷卻系統和一为個人冷卻系統。爲了縮小微型蒸氣壓縮製冷系統的尺寸，系統的元件必須小型化。系統的壓縮機是在市場上直接购買的，但是換熱器包括冷板蒸發器、管翅式蒸發器和微通道冷凝器都是特別設計和製造的。實驗裝置建成可以方便的改變工作條件，諸如壓縮機轉速、製冷劑充灌量、毛細管長度、換熱器面積等。<br>4) 對電子冷卻系統和個人冷卻系統分別進行了實驗。對於電子散熱系統來，當發熱管的功率為200瓦時，冷板溫度可以控制在大約60攝氏度。系統的熱力學完善度在0.23到0.31，而壓縮機的效率介乎40%至65%。對個人冷卻系統來，系統製冷量可達321瓦，其性能係數達到4.59。系統的熱力學完善度為0.21 ~ 0.27。 兩种系統的熱力學完善度都與當前家用製冷系统的熱力學完善度相似。相信不久的将来会有不少应用。<br>Micro refrigeration systems are being increasingly used nowadays. One example is electronic cooling. With the rapid advancement of chips, traditional passive heat dissipation techniques are becoming obsolete and hence, new active cooling techniques become necessary. The other example is the personal thermal comfort system demanded by people working in the hazardous environment, such as fire fighting. Among various cooling methods, Vapor Compression Refrigeration (VCR) is the most promising method. According literatures, however, few miniature refrigeration systems are available.<br>This thesis presents two Miniature Vapor Compression Refrigeration (MVCR) systems, one for electronics cooling and the other for personal thermal comfort. In particularly, following aspects are focused:<br>1) Thermodynamic analysis. The thermodynamic models of the systems are developed and the performances are studied under various working conditions including compressor efficiencies, ambient temperature and so on.<br>2) Entropy analysis. It is found that entropy of the compressor and the heat leakage play crucial roles. High efficient compressor and the heat leakage minimization are very important.<br>3) Prototype building. Two prototypes are built: one for electronics cooling and the other for personal thermal comfort. The miniature compressors are purchased from market. The heat exchangers, including the cold pate, tube-fin evaporator and micro channel condenser, are custom designed and made.<br>4) Experiment testing. The two prototypes are tested under various working conditions such as compressor speed, refrigerant charge and capillary tube length. For the electronics cooling system, the cold plate temperature could be maintained at about 60 ºC under the 200 W heater power input. The second-law efficiency of the system varies from 0.23 to 0.31; and the compressor efficiency is between 40% ~ 65%. For the personal thermal comfort system, its capacity could reach 321 W with 100 g refrigerant charge, 1200 mm capillary tube length, and the compressor speed of 4503 rpm. The COP is 4.59 and the second-law efficiency is between 0.21 ~ 0.27. The performances of the two systems are comparable to that of the current domestic refrigeration systems. Therefore, it is expected that they will find some practical applications in the near future.<br>Detailed summary in vernacular field only.<br>Detailed summary in vernacular field only.<br>Detailed summary in vernacular field only.<br>Detailed summary in vernacular field only.<br>Detailed summary in vernacular field only.<br>Detailed summary in vernacular field only.<br>Wu, Zhihui.<br>Thesis (Ph.D.)--Chinese University of Hong Kong, 2012.<br>Includes bibliographical references (leaves 99-110).<br>Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.<br>Abstract also in Chinese.<br>Abstract --- p.I<br>Acknowledgement --- p.IV<br>List of Tables --- p.VIII<br>List of Figures --- p.IX<br>Nomenclature --- p.XII<br>Chapter Chapter 1 --- Introduction --- p.1<br>Chapter 1.1 --- Backgound --- p.1<br>Chapter 1.2 --- Thesis Outline --- p.5<br>Chapter Chapter 2 --- Literature Review --- p.6<br>Chapter 2.1 --- History of Refrigeration --- p.6<br>Chapter 2.2 --- Availabe Refrigeration Methods --- p.7<br>Chapter 2.2.1 --- Heat pipe and vapor chamber --- p.9<br>Chapter 2.2.2 --- Thermoelectric cooler --- p.10<br>Chapter 2.2.3 --- Stirling refrigerator --- p.10<br>Chapter 2.2.4 --- Pulse tube refrigerator --- p.11<br>Chapter 2.2.5 --- Absorption refrigerator --- p.12<br>Chapter 2.3 --- Vapor Compression Refrigeration System --- p.14<br>Chapter 2.3.1 --- Development of the miniature refrigeration system --- p.15<br>Chapter 2.3.2 --- Development of the miniature compressors --- p.20<br>Chapter 2.3.3 --- Development of the micro heat exchangers --- p.24<br>Chapter 2.3.4 --- Applications --- p.28<br>Chapter Chapter 3 --- System Analsysis and Components Design --- p.29<br>Chapter 3.1 --- A Brief Review of a Typical VCR System --- p.29<br>Chapter 3.1.1 --- Refrigerant comparison --- p.33<br>Chapter 3.1.2 --- Effect of the compressor efficiency --- p.34<br>Chapter 3.1.3 --- Effect of the ambient temperature --- p.35<br>Chapter 3.1.4 --- Effect of the evaporator temperature --- p.36<br>Chapter 3.2 --- Analysis on Entropy Generation of a MVCR System --- p.37<br>Chapter 3.2.1 --- Derivation of coefficient of performance --- p.38<br>Chapter 3.2.2 --- Entropy generation calculation for a MVCR system --- p.39<br>Chapter 3.3 --- System Design --- p.46<br>Chapter 3.3.1 --- System Configuration --- p.46<br>Chapter 3.3.2 --- Heat Exchanger Design --- p.47<br>Chapter 3.3.2.1 --- Condenser design --- p.48<br>Chapter 3.3.2.2 --- Cold plate design --- p.50<br>Chapter 3.3.2.3 --- Tube-fin evaporator design --- p.51<br>Chapter Chapter 4 --- The MVCR System for Electronics Cooling --- p.55<br>Chapter 4.1 --- Experimental Setup --- p.55<br>Chapter 4.1.1 --- Components --- p.55<br>Chapter 4.1.2 --- Instrumentation --- p.61<br>Chapter 4.1.3 --- Testing plans --- p.63<br>Chapter 4.1.4 --- Data reduction --- p.64<br>Chapter 4.1.5 --- Uncertainty analysis --- p.67<br>Chapter 4.2 --- Results and Discussion --- p.68<br>Chapter 4.2.1 --- Effect of the compressor speed --- p.68<br>Chapter 4.2.2 --- Effect of the refrigerant charge --- p.70<br>Chapter 4.2.3 --- Effect of the capillary tube length --- p.71<br>Chapter 4.2.4 --- Cold plate temperature comparison --- p.72<br>Chapter 4.2.5 --- Location of the Cartridge heater --- p.76<br>Chapter 4.2.6 --- System efficiency --- p.78<br>Chapter 4.2.7 --- Thermal resistance --- p.81<br>Chapter 4.3 --- Summary --- p.83<br>Chapter Chapter 5 --- The MVCR System for Personal Cooling --- p.85<br>Chapter 5.1 --- Experimental Setup --- p.85<br>Chapter 5.2 --- Results and Discussions --- p.87<br>Chapter 5.2.1 --- Effect of the compressor speed --- p.87<br>Chapter 5.2.2 --- Effect of the refrigerant charge --- p.88<br>Chapter 5.2.3 --- Effect of the capillary tube length --- p.89<br>Chapter 5.2.4 --- Effect of the evaporator area --- p.90<br>Chapter 5.2.5 --- Effect of the evaporator fan speed --- p.91<br>Chapter 5.2.6 --- System efficiency --- p.92<br>Chapter 5.3 --- Summary --- p.94<br>Chapter Chapter 6 --- Conclusions and Future Work --- p.96<br>Chapter 6.1 --- Conclusions --- p.96<br>Chapter 6.2 --- Future Work --- p.98<br>Bibliography --- p.99

碩士<br>國立勤益科技大學<br>冷凍空調系<br>99<br>A variable frequency drive refrigeration system is built up to study the variable speed characteristics. The Vedas are used in the drives of compressor, evaporator fan, condenser fan, to change the speed. The step-motored electronic expansion valve is used in the refrigeration system to control the refrigerant flow rate. The test system can change the evaporator and condenser inlet temperature by mix the leaving air from evaporator, condenser and outlet air in the circulation air duct. The evaporating and condensing temperatures are controlled from the inlet air temperature. The flow coefficient of the electronic expansion valve is obtained in the study. The step response of the electronic expansion valve, compressor speed, evaporator fan and condenser fan are tested in the results. The control stability test of the electronic expansion valve is shown in the results. The results of this study can provide a reference to the design of variable speed refrigeration system.

碩士<br>國立勤益科技大學<br>冷凍空調系<br>100<br>The expansion valve and capillary tube are tested to see the effect of the valve open degree, capillary tube length and degree of subcool on the system. The capillary tube and expansion valve are also combined in series or parallel to improve the modulation characteristics. The inlet quality effect is also tested in the expansion valve to examine the variation of valve rangeability. The oversized expansion valve can be only modulated between 6% ~ 15% in the valve open test, which shows a low rangeability. In the subcool test, the valve inlet subcool has a greater effect on the capillary tube performance as compared with the expansion valve. To improve the modulating ability of the oversized valve, the capillary valve（in the front）are connected with the expansion valve（in the rear）in series after the sensitivity the capillary tube inlet subcool sensitivity were investigated. The valve modulation range can be improved from 6% ~ 15% to 35% ~ 70 % after cascading the capillary tube in the front, and the evaporating pressure and condensing pressure change small during vale modulation. The maximum refrigerant flow rate is limited by the capillary tube even the valve opens to the outside of the original modulating range. The rangeability of electronic expansion is usually smaller than 0 ~100%. The parallel coupled expansion device can extend the rangeability to nearly 0 ~100% after coupled with capillary tube in parallel. An undersized expansion valve coupled with a long capillary tube in parallel is tested. The flow is through the capillary tube as the valve is closed. The refrigerant flows through the tube and valve simultaneously when the vale begins to open. The capacity can be modulated effectively as the valve opens in accordance with the compressor speed variation. The expansion can still modulate the refrigerant flow even as the inlet refrigerant is in the two-phase region.