[pt] Apresenta-se neste trabalho uma análise termodinâmica comparativa entre o desempenho de um ciclo de refrigeração que usa um ejetor como um pré-expansor do fluido refrigerante e um ciclo padrão de refrigeração por compressão de vapor. Na primeira etapa do trabalho é desenvolvido um modelo matemático em regime é desenvolvido um modelo matemático em regime permanente baseado na primeira Lei da Termodinâmica para cada um dos ciclos estudados. O modelo é capaz de prever o funcionamento de cada um dos componentes do ciclo, assim como do sistema geral. Ao modelo do ejetor é dada uma especial atenção. Para este componente do sistema apresenta-se uma simulação de desempenho, isto é, a partir de condições termodinâmicas previamente estabelecidas, seu modelo matemático é resolvido separadamente através de um processo iterativo pelo método sequencial de solução. Na segunda etapa do trabalho é apresentada para cada um dos equipamentos de cada ciclo uma análise, também em regime permanente, baseada na Segunda Lei da termodinâmica, ou análise Exergética. Os resultados encontrados demonstram que teoricamente, o uso de um ejetor nas condições propostas no trabalho, melhora de maneira significativa o desempenho de um ciclo padrão de refrigeração por compressão de vapor. / [en] The present work is about a comparative thermodynamics performance analysis between a refrigeration cycle that uses an ejector as a refrigerant expander and a standard vapor compression cycle. In the first step, a steady state mathematical model based on the first law of thermodynamics is developed for each one of previous cycles. A special attention is given to the ejectors model. A performance simulation is shown to this component, from previously thermodynamics conditions set up your mathematical mode is separately solved through a iterative process by a sequential solution method. In the second step a second Law of thermodynamics, or exergy analysis, in the steady state, is presented for each one of the equipament of the cycles. The obtained results showed that theoretically, the use of an ejector at the proposed conditions of this work, improves in a significant way the performace of standard vapor- compression cycle.

Nowadays efficiency measures are more and more important because the price of the energy is increasing every year. Moreover, saving energy it is also important for decrease the environmental impact. Kastvallen is a hockey arena built in 1997 that cools the hockey rink with electric compressors. The changing rooms are heating by using district heating. Actually the total invoice of electricity is above the 800000 SEK. Meanwhile the district heating invoice reaches the 60000SEK. The aim of this project is reducing the amount of the electricity and heat invoice promoting smart energy improvements. The improvements proposals can be divided in three sections; energy savings of the changing rooms, efficiency increase of the compressors and dehumidifier energy savings. For heat the tap water and the changing room’s ventilation it is suggested to take profit from the heat released at the condenser and so reduce its heat load requirements. For this proposal two different configurations are studied. In order to increase the efficiency of the compressors the possibility of reducing the condenser temperature will be studied. Three proposals will be studied to carry out this commitment; Installing a condensing temperature control, installing a evaporate cooler and having a snow storage. Finally, one of the largest consumers of electricity in Kastvallen ice hockey rink is the dehumidifier. The current dehumidifier works with a desiccant wheel. The desiccant material extract the moisture from the processed air flow, after that the desiccant has to be reactivated with ‘fresh air’. This reactivation air needs to be heated 95ºC, so the waste air released after the reactivation of the desiccant is air at high temperature. The first proposal is preheat the reactivation air with the hot waste air in order to reduce the heating requirements, conducting this proposal the total money saved each year would be 41811 SEK with a Pay-back around 1 year. The second step is studied the possibility of heating the air with district heating, taking into account that district heating is three times cheaper than electricity, conducting this proposal the total money saved each year would be 45629 SEK with a Pay-back around 1 year. The last proposal is to combine preheating and heating with district heating, conducting this proposal the total money saved each year would be 61553 SEK with a Pay-back around 1.6 years. All the previous energy improvements proposals are studied with empirical and analytical methods and using the knowledge gained during the previous years of studies. The study concludes that the best proposal for the dehumidifier is combine the preheating and heating with district heating. In addition of the money saved, this measure allows to save 2.71 Tm of CO2 each year. For the refrigeration cycle, the study concludes that installing a controlled temperature control is the best option if the price of that is lower than 334726 SEK. If not the best option is heating the rooms and the ventilation with the condenser of the refrigeration cycle. These measures could reduce between 8% and 20% of the total energy invoice plus a considerable reduction of CO2 emissions. Evaporative cooling and snow storage would be studying after with the data of the first year of the condensing temperature control; if it is installed.

This work suggests a new multiple ejector refrigeration cycle operated by an NGL Recovery Plant's waste heat as a replacement to the mechanical compression refrigeration cycle. This will result in significant power reduction and CO2 emission reduction. / Typical NGL plant compresses its feed to a high pressure (3040 kPa). The feed gas compressors’ discharge reaches approximately 150 OC. After that, the feed is cooled by three-stage propane vapour compression refrigeration cycle. This paper examines various options for thermal power cooling in such plants in order to eliminate part of the propane chilling system. Since most of the new plants are located in desert climates, typical designs based on absorption refrigeration are not very efficient. Design proposed in this work employs ejector refrigeration and it is based on 45 OC air as a cooling media (summer conditions in hot climates). Performance factor has been defined as the total cooling provided by the refrigeration system over the total cooling required in the 1st cooling stage of the NGL Recovery Plant. Cooling based on a single N-pentane ejector cycle with N-pentane has COP of 0.342 and performance factor (ƞ) of 0.842. Multistage ejector N-pentane refrigeration system has COP of 0.714 and performance factor (ƞ) of 1.053. For a typical 750 Million scf/d NGL plant, the new design saves $12 Millions in capital costs and $1.5 in annual electricity cost. / Thesis / Master of Applied Science (MASc)

Compressed air is widely used particularly in industry. In order to increase the quality of the process and lifetime of the machine, the compressed air should be dried. Therefore the air is used after compression and drying processes. The most commonly used machines that do this process are called &ldquo / Refrigerant Air Dryers&rdquo / . These air dryers are designed to cool and dehumidify the moist air. The process of decreasing temperature is carried out by a refrigerant, R134a. Unlike design conditions, dryers are working in variable loads (variable compressed air flow rates). An experimental setup is prepared for analyzing the variance on the machine and the performance under these variable loads. This thesis includes the design, preparation and the modification of the refrigeration experimental setup for refrigerant air dryers. The setup is tested under three different conditions and the results are compared.

Interest in utilizing solar-driven refrigeration systems for air-conditioning or refrigeration purposes has grown continuously. Solar cooling is com-prised of many attractive features and is one path towards a more sus-tainable energy system. Compared to solar heating, the cooling load, par-ticularly for air-conditioning applications, is generally in phase with solar radiation. The objective of this thesis is to establish a fundamental basis for further research and development within the field of solar cooling. In this thesis, an overview of possible systems for solar powered refrigeration and air-conditioning systems will be presented. The concept of the ‘Solar Cool-ing Path’ is introduced, including a discussion of the energy source to the collector, and choice of cooling cycle to match cooling load. Brief infor-mation and comparisons of different refrigeration cycles are also pre-sented. The performance of solar cooling systems is strongly dependent on local conditions. The performance of a solar divan air-conditioning system in different locations will therefore be compared in this thesis. Solar cooling systems can be efficiently operated in locations where sufficient solar ra-diation and good heat sink are available. A solar-driven ejector refrigeration system has been selected as a case study for a further detailed investigation. A low temperature heat source can be used to drive the ejector refrigeration cycle, making the system suitable for integration with the solar thermal collector. Analysis of the solar driven ejector system is initiated by steady state analysis. System performance depends on the choice of working fluid (refrigerant), oper-ating conditions and ejector geometry. Results show that various kinds of refrigerants can be used. Also, thermodynamic characteristics of the re-frigerant strongly influence the performance of the cycle. An ejector re-frigeration cycle using natural working fluids generates good perform-ance and lower environmental impact, since traditional working fluids, CFC’s and HFC’s are strong climate gases. Further on, exergy analysis is used as a tool in identifying optimum operating conditions and investi-gating losses in the system. Exergy analysis illustrates that the distribu-tion of the irrervsibilities in the cycle between components depends strongly on the working temperatures. The most significant losses in the system are in the solar collector and ejector. Losses in the ejector pre-dominate over total losses within the system. In practice, the cooling load characteristic and solar radiation are not constant. Therefore, a dynamic analysis is useful for determining the characteristics of the system during the entire year, and dimensioning the important components of the solar collector subsystem, such as storage tanks. The final section of the thesis will deal with the ejector, the key compo-nent of the ejector refrigeration cycle. Characteristics of the actual ejector are shown to be quite complicated and its performance difficult to de-termine solely through theoretical analysis. Suggested design procedures and empirical equations for an ejector are offered in this thesis. Prelimi-nary test results for one fixed ejector dimension using R134a as the re-frigerant are also included. / QC 20100916

Cooling of electronic equipments has become an important issue as the advances in technology enabled the fabrication of very small devices. The main challenge in cooling is the space limitation. The use of miniature refrigerators seems to be a solution alternative for the cooling problem. The objective of this study is to design and simulate a vapor compression refrigeration cycle for a micro-scale refrigerator. A MATLAB code is developed for the simulations. The four components of the refrigerator, namely, the condenser, evaporator, compressor and the capillary tube are designed separately. The cycle is successfully completed nearly at the same point where it begins. The cold space temperature, ambient air temperature, condensation and evaporation temperatures, and the evaporator heat load are the predetermined parameters. A fan is used to cool the condenser, and the compressor is selected as isentropic. R-134A is selected as the refrigerant and a simple interpolation code is developed to obtain the thermophysical properties of R-134A. The original design is carried out with an isentropic compressor. For the purpose of comparison, a cycle with a polytropic compressor is also considered. Similarly, two alternative designs for the evaporator are developed and simulated. A second law analysis is performed at the end of the study.

[pt] O presente trabalho analisa experimentalmente um ciclo de refrigeração por absorção operando em regime transiente. Estuda-se, desta forma, a possibilidade do uso do ciclo de refrigeração por absorção em veículos automotores para condicionamento de ar. O ciclo de absorção utilizaria, como fonte térmica, os gases de exaustão ou a água de refrigeração do motor. Esta fonte de calor está disponível, geralmente, em condições variáveis de temperatura e potência. O trabalho foi dividido em três etapas. Na primeira delas é analisado o desempenho do ciclo de absorção funcionando com uma resistência elétrica de potência variável. Nesta etapa os parâmetros do ciclo foram determinados, assim como as temperaturas em diversos pontos do sistema. Na segunda etapa, foi utilizado um soprador térmico que simula os gases de exaustão de um motor a combustão interna. Na eventualidade da utilização do ciclo para o condicionamento de ar em aplicações automotivas, o uso dos gases de exaustão do motor de combustão interna reduziria o consumo de combustível do veículo, visto que o ciclo de absorção não exige potência mecânica do motor, tal como no ciclo tradicional de compressão de vapor. Há vantagens, também, nos itens relativos a manutenção e impacto ambiental. Como a carga e velocidade de um motor são variáveis, as temperaturas do ciclo sofrem variações muito rápidas. Tal problema foi minimizado com o uso de um regenerador estático, na terceira fase do trabalho, que impõe uma inércia térmica ao sistema, atenuando, desta forma, estas oscilações de temperatura. / [en] The present work is related to an experimental analysis of an absorption refrigeration cycle operating in transient regime, leading to the study of the techcnical feasibilty for the application of absorption refrigeration cycles in automotive air conditioning systems. In such system, waste heat from the exhaust or cooling systems acts as the heat source for the cycle. This heat source is typically variable in power and temperature. The work is divided din three parts. First, the steady state performance of the cycle, operating with an electrical resistance as the heat source, is studied. In the second part of the work, an electrical blower simulates the flow of exaust gases from an internal combustion engine. If compared with traditional vapor compression cycles for automotive applications, absorption refrigeration cycles have the advantage of not requiring mechanical power from the engine, as well as presenting less environmental impact and ease of maintainance. Power and rotational speed may vary rapidly and considerably in internal combustion engines. To cope with a varying heat source, the use of a static regenerator is studied in the third part of the work. This use confirmed the expectations of having temperature and power variations considerably attenuated.

Orientador: Jose Vicente Hallak D'Angelo / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-11T14:06:54Z (GMT). No. of bitstreams: 1 Cipolato_Liza_M.pdf: 1029854 bytes, checksum: e29def5b437d5ad6a00d8fc677c63bf5 (MD5) Previous issue date: 2008 / Resumo: O comércio de gás natural liquefeito apresenta um crescente interesse por parte tanto de países exportadores como dependentes desta fonte energética. Apesar de o transporte por gasoduto ser muito menos suscetível a perdas, ele se torna inviável a longas distâncias ou a demandas variáveis. A liquefação do gás natural também proporciona o armazenamento desta fonte energética numa forma estável e de alto potencial energético,evidenciando o caráter estratégico do processo. Desde a década de 60 a tecnologia para liquefação do gás natural é utilizada, porém, apenas há alguns anos os países iniciaram o comércio desta fonte energética em larga escala e isto acarretará um aumento mundial tanto no número de terminais exportadores (plantas de liquefação) quanto importadores (terminais de regaseificação). O processo de liquefação do gás natural ocorre através de uma sequência de ciclos termodinâmicos de refrigeração, e estes, por sua vez, precisam trabalhar de forma otimizada para reduzir perdas. A análise exergética é uma ferramenta muito útil para avaliar estas perdas e pode ser essencial na instalação de uma nova planta ou melhoria de uma já existente. O presente trabalho realizou uma análise exergética de um ciclo de refrigeração utilizado para a liquefação de gás natural, o qual é do tipo multiestágio em cascata, padrão utilizado atualmente, sendo o mais conhecido e difundido entre as indústrias da área. Primeiramente, o processo foi simulado em software comercial Hysys (versão 3.2 da Aspen Technology). O resultado obtido da simulação foi validado através de comparação com dados da literatura, mostrando-se adequado. Em seguida, a simulação foi testada em diferentes condições operacionais, seguindo um planejamento fatorial completo, o qual teve como objetivo verificar a influência da variação das pressões de seis pontos específicos do ciclo sobre a variável resposta, que é a taxa de exergia total destruída no processo, visando sua minimização. Os resultados obtidos levaram a uma nova condição de operação para o ciclo de refrigeração com redução de aproximadamente 48% da taxa de exergia destruída com relação aos dados do caso obtido da literatura. Tal resultado evidencia o potencial da metodologia termodinâmica utilizada, demonstrando sua aplicação em estudos de melhoria do desempenho de ciclos de refrigeração para a indústria de liquefação de gás natural / Abstract: The liquefied natural gas trade shows a growing interest either from countries which are exporters or countries which depend on this kind of energetic source. Although gas pipelines are less susceptible of transportation losses, they become impracticable when distances are too long or when demands are highly variable. The liquefaction of natural gas also enables its storage in a stable way, in which energetic potential is high, expressing the strategic purpose of the process. Since the 1960 decade natural gas liquefying technology is been used, but only a few years ago countries have started the trade of this kind of energetic source on a large scale. Consequently, the number of exporter terminals (liquefaction industries) and importer terminals (regasification plants) will increase worldwide. The natural gas liquefaction process is based on a sequence of refrigeration thermodynamics cycles, which need to work in an optimized way in order to reduce losses. The exergy analysis is a very useful tool to evaluate these losses and can be crucial in a new plant installation or in a current one improvement. This dissertation performed an exergy analysis of a multistage cascade refrigeration cycle applied in natural gas liquefaction. The multistage cascade cycle is currently the standard type, being the most known and diffused among industries. Firstly, the process was simulated in commercial software Hysys (version 3.2 of Aspen Technology). The result obtained from the simulation was validated by comparison with the literature data and showed a very adequate similarity. After that, the simulation was checked in different operational conditions, according to the complete factorial design of experiments. The design of experiments¿ objective was to verify the pressure influence of six specific points of the cycle over the response variable, which is the rate of total exergy destroyed in the cycle, in order to reach its minimal value. The results showed a new operational condition to the refrigeration cycle, in which the destroyed exergy rate was reduced by approximately 48% in comparison with literature data. This result provides evidence of the high potential of the thermodynamic tool used, showing its application in studies of performance improvements for refrigeration cycles in industries of natural gas liquefaction / Mestrado / Sistemas de Processos Quimicos e Informatica / Mestre em Engenharia Química

L’objectif de cette étude est d’optimiser un cycle frigorifique au CO2 pour une application dans le transport frigorifique. Les performances de l’unité doivent être supérieures à celles d’une machine avec une injection de vapeur et un compresseur bi-étagé déjà commercialisé. Suite à l’étude de plusieurs solutions, un éjecteur couplé à un échangeur interne semble la solution la plus intéressante.Un banc expérimental est créé à partir de l’unité possédant une injection de vapeur. L’éjecteur est muni d’une aiguille pour pouvoir assurer une recherche de la haute pression optimale. L’échangeur interne est équipé d’un by-pass pour modifier la puissance échangée. Un ensemble de points d’essais est testé avec deux températures d’évaporation : 0 °C et -20 °C, et trois températures de source chaude : 30 °C, 38 °C et 50 °C.L’éjecteur avec aiguille est capable de s’adapter à différentes températures extérieures en modifiant la haute pression. L’échangeur interne permet d’augmenter les performances du cycle mais présente une limite, la température au compresseur devient élevée et présente un risque de détérioration de ses performances ou de l’huile.Avec le cycle présentant un éjecteur, une amélioration du coefficient de performance est observée pour les points avec une température d’évaporation de 0 °C mais celle-ci chute drastiquement pour les températures d’évaporation de -20 °C. Une analyse exergétique du cycle confirme les faibles performances de celui-ci pour des températures d’évaporation négatives.À partir des résultats expérimentaux, des modèles numériques sont mis en place. Les échangeurs, vannes de détente sont modélisés de manière conventionnelle. Pour le compresseur, le modèle de Winandy est modifié afin de fonctionner pour un compresseur bi-étagé avec injection de vapeur. L’éjecteur est modélisé à travers un modèle unidimensionnel basé sur des transformations simplifiées décrites à travers des rendements isentropiques. Tous les modèles sont validés mais ceux des échangeurs ont un temps de calcul CPU trop important pour pouvoir être utilisés sur une modélisation dynamique. / The aim of this study is to optimize a CO2 cooling cycle for transport application. The efficiency of the unit needs to be superior that of a cycle with vapor injection and a two stages compressor. The solution proposed is to install an ejector with an internal heat exchanger.A test bench is created from a pre-existing unit. Tests are made for two evaporation temperatures: 0 °C and -20 °C and three external temperatures: 30 °C, 38 °C and 50 °C. The ejector is equipped with a needle to seek the optimal high pressure. The internal exchanger is equipped with a by-pass to modify the thermal power exchanged.The ejector with needle can change the high pressure to seek the optimal conditions. The internal heat exchanger increases the efficiency of the cycle but the rising of temperature at the compressor can degrade its efficiencies or the oil. The new cycle increases the COP for evaporation temperature of 0 °C but the COP is lower than without ejector for evaporation temperature of -20 °C. An exergetic analysis shows that indeed the cycle is less efficient for low evaporation temperature.From the experimental results, numerical models are created to realize a system simulation and to test different scenarii to drive the unit. Exchangers and valves modeled with conventional tools. Wynandy’s model is adapted to be used on a two-stage compressor with vapor injection. The ejector is modeled with a one-dimensional model, based on simplified transformations described with isentropic efficiencies. All models seem to work but the CPU time is too high to use the exchanger models for dynamic simulation.

In this thesis, performance of a heat pump aided by solar heating system with an evacuated tubular collector has been analyzed theoretically and experimentally. For this purpose, a domestic hot water heating system has been designed, constructed and tested. The evacuated tubular solar collector has been used to achieve higher collector efficiency in winter. The fraction of the solar energy utilized has been measured experimentally and estimated theoretically. Effects of various parameters have been investigated on the performance of the proposed system. A mathematical model was developed to investigate the effects of different environmental, design and operational parameters on the solar heating system. In order to compare the obtained theoretical results with experimental ones, an experimental study has been carried out. For that, a number of experiments have been made at the solar house of the Mechanical Engineering Department of METU. An air-to-air heat pump was integrated with an evacuated tubular solar water heater unit (closed water circulation) and the performance of it has been studied experimentally. As a result of the experimental study, the maximum value of the coefficient of performance of the solar assisted heat pump used in this study was obtained as 4.85. The second law efficiency of the system was between 4.8-27.4 %.