This thesis is aimed to study the heat and mass transfer performance of a generator for the absorption cooling system. Both aqueous lithium bromide (LiBr) and lithium chloride (LiCl) solutions are studied. The generator inlet concentration and outlet concentration are set to 55% and 60%, respectively, for aqueous lithium bromide solution, and 40% and 45%, respectively, for aqueous lithium chloride solution. Therefore, the system of falling film desorption process is studied for the simulation of the generator. A finite-difference method is applied to numerically simulate the heat and mass transfer for a falling film desorption process in the generator. Parameters effects the inlet temperature, the heat source (wall) temperature, and the vapor pressure consistent with the saturation pressure of the condenser, and the solution flow rate are studied. The results of the present study provide important design references for absorption cooling systems.

The air conditioning systems currently utilized in automobiles are the vapor compression systems. This type of system has many disadvantages: the refrigerant used is not environmentally friendly, the compressor is in competition with the engine coolant system, and the compressor uses a significant portion of the engine power. A waste heat driven absorption refrigeration system is one alternative to the current systems that could address these problems. The absorption refrigeration system uses solutions for the absorbent-refrigerant pair that do not harm the environment. This investigation includes a theoretical analysis of the feasibility of absorption air conditioning system in automotive applications. Also, a comparison of the power requirements of the proposed system and the vapor compression system is performed.

This study explores the application of micro-CCHP systems that utilize a 30 kW gas microturbine and an absorption chiller. Engineering Equation Solver (EES) is used to model a novel single-effect and double-effect water-lithium bromide absorption chiller that integrates the heat recovery unit and cooling tower of a conventional CCHP system into the chiller’s design, reducing the cost and footprint of the system. The results of the EES model are used to perform heat and material balances for the micro-CCHP systems employing the novel integrated chillers, and energy budgets for these systems are developed. While the thermal performance of existing CCHP systems range from 50-70%, the resulting thermal performance of the new systems in this study can double those previously documented. The size of the new system can be significantly reduced to less than one third the size of the existing system.

This thesis consists of two different research problems. In the first one, the aim is to model and simulate a solar-powered, single-effect, absorption refrigeration system using a flat-plate solar collector and LiBr-H2O mixture as the working fluid. The cooling capacity and the coefficient of performance of the system are analyzed by varying all independent parameters, namely: evaporator pressure, condenser pressure, mass flow rate, LiBr concentration, and inlet generator temperature. The cooling performance of the system is compared with conventional vapor-compression systems for different refrigerants (R-134a, R-32, and R-22). The cooling performance is also assessed for a typical year in Tampa, Florida. Higher COP values are obtained for a lower LiBr concentration in the solution. The effects of evaporator and condenser pressures on the cooling capacity and cooling performance are found to be negligible. The LiBr-H2O solution shows higher cooling performance compared to other mixtures under the same absorption cooling cycle conditions. For typical year in Tampa, Florida, the model shows a constant coefficient of performance of 0.94. In the second problem, a numerical model is developed for a typical food retail store refrigeration/HVAC system to study the effects of indoor space conditions on supermarket energy consumption. Refrigerated display cases are normally rated at a store environment of 24ºC (75ºF) and a relative humidity of 55%. If the store can be maintained at lower relative humidity, significant quantities of refrigeration energy, defrost energy and anti-sweat heater energy can be saved. The numerical simulation is performed for a typical day in a standard store for each month of the year using the climate data for Tampa, Florida. This results in a 24 hour variation in the store relative humidity. Using these calculated hourly values of relative humidity for a typical 24 hour day, the store relative humidity distribution is calculated for a full year. The annual average supermarket relative humidity is found to be 51.1%. It is shown that for a 5% reduction in store relative humidity that the display case refrigeration load is reduced by 9.25%, and that results in total store energy load reduction of 4.84%. The results show good agreement with available experimental data.

Vapor absorption systems offer advantages over vapor compression systems for air-conditioning systems in some applications. They use heat as their primary energy input and hence provide opportunities to use solar energy or waste heat to drive these systems. The absorber is the most crucial component of the vapor absorption system and has the largest impact on its performance. Absorber design requires a keen understanding of the underlying heat and mass transfer processes in the absorber. The horizontal tube geometry is by far the most popular absorber geometry, due to the high absorption efficiencies achievable without incurring commensurate pressure drops. Several models have been proposed in the literature to model the heat and mass transfer during absorption over horizontal tube banks. However all of them make very simplistic assumptions about the flow profiles in the absorber. High speed flow visualization studies in the literature have shown that the flow occurs in the form of droplets and the formation and the detachment of these droplets and their impact on the tube has significant effects on the heat and mass transfer. Most absorption models in the literature neglect these flow modes and assume the solution to flow as a uniform film. The present study attempts to numerically model the heat and mass transfer in the absorber taking the realistic drop-wise and wavy film flow patterns into consideration. The impact of the fall of these droplets on the tube causes the lithium bromide solution present on the film on the tube to mix and present newer regions of the solution for vapor absorption. The impact of the droplets also causes waves that propagate axially over the liquid film on the tube. The mixing effect and the waves caused due to droplet impact play a very important role in the heat and mass transfer. Results obtained from this study will aid in better understanding of the vapor absorption process, and in the design of more efficient absorbers.

Orientador: Elaine Maria Cardoso / Resumo: Sistemas de refrigeração são indispensáveis para o modo de vida do homem atual, porém o grande gasto energético, de fontes não renováveis, e os impactos ambientais, levam-nos a estudar e a pensar em outras fontes de energia, de preferência renováveis, e em outros ciclos de refrigeração com gasto energético menor. Este trabalho tem como objetivo a modelagem de um sistema de refrigeração por absorção de vapor para o conforto térmico de ambientes, verificando a viabilidade desse sistema de refrigeração para aplicação em salas de aula. No presente trabalho mostra-se o sistema de refrigeração como sendo umas das alternativas ao sistema de refrigeração por compressão de vapor, o qual possui um alto gasto energético. Para o funcionamento do sistema de refrigeração por absorção de vapor foi proposto a energia solar como fonte de energia térmica do gerador, pois em regiões como Rio Verde – GO (localizada na região de latitude 17°47’S e longitude 50°58’W, onde o clima tropical predomina em quase todos os meses do ano, com temperatura mínima de ~20 ° C e máxima de ~30 °C) o condicionamento do ambiente é imprescindível. Foi utilizado o software EES para a simulação e modelagem do sistema de absorção de vapor, baseado nas trocas de calor entre os componentes desse sistema, desprezando perdas energéticas e de pressões que ocorrem em um ciclo real de absorção de vapor. As simulações e resultados mostraram que, nessa região tropical, o clima é propício para o uso de energia solar e que sua t... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Cooling systems are indispensable for today's man's way of life, but the high energy expenditure from non-renewable sources and environmental impacts lead us to study and think about other sources of energy, preferably renewable, and in other refrigeration cycles with lower energy expenditure. The objective of this work is the modeling of a vapor absorption refrigeration system for the thermal comfort of environments, verifying the viability of this refrigeration system for application in classrooms. In the present work is shown the refrigeration system as one of the alternatives to the system of refrigeration by compression of steam, which has high energy expenditure. For the operation of the vapor absorption refrigeration system, solar energy was proposed as the generator's thermal energy source, since in regions such as Rio Verde - GO (located in latitude 17° 47' S and longitude 50° 58' W, where the tropical climate prevails in almost every month of the year, with a minimum temperature of ~ 20° C and maximum of ~ 30° C), the ambient air-conditioning is essential. EES software was used for the simulation and modeling of the vapor absorption system based on the heat exchanges between the components of this system, disregarding energy and pressures losses that occur in a real vapor absorption cycle. The simulations and results showed that, in this tropical region, the climate is favorable to use solar energy and its transformation into thermal energy is sufficient for the ope... (Complete abstract click electronic access below) / Mestre

Made available in DSpace on 2015-05-08T14:59:44Z (GMT). No. of bitstreams: 1 Arquivototal.pdf: 5206307 bytes, checksum: 032db8e5ad423ee5a0fc6cfc786bd065 (MD5) Previous issue date: 2012-09-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The present study describes a theoretical and experimental analysis of the Prototype 01, this being an absorption refrigeration machine of simple effect with the pair water-lithium bromide as a working fluid and uses natural gas as an energy source for the steam generator, aiming the simulation of waste heat cogeneration. The unit has been developed and constantly improved in Rede Cooperativa de Pesquisa Norte/Nordeste do Gás Natural RECOGÁS-N/NE building present in Instituto de Energia Sustentável (IES) at the Universidade Federal da Paraíba. This unit has a carbon steel frame, using a stainless steel pipe. One goal of the study is an approximation of the results obtained experimentally in this study with the theoretical results for SANTOS (2005). In order to purpose validation was used Engineering Equation Solver (EES) software to obtain the properties, especially those inherent to the working fluid, using input data obtained experimentally. Still aims to expose inherent and unique aspects of an essentially experimental work, which will be addressed experimental methodology applied by the use of the materials used, the discussions regarding aspects of construction and operation of the unit, problems identified, interventions in the pilot plant and finally proposing solutions to some of the observed problems. / O presente estudo descreve uma análise teórico-experimental do Protótipo 01, este sendo uma máquina de refrigeração por absorção de simples efeito com o par água brometo de lítio como fluido de trabalho e que utiliza gás natural como fonte energética para o gerador de vapor, visando a simulação de cogeração de rejeitos térmicos. A unidade vem sendo desenvolvida e constantemente aperfeiçoada no prédio da Rede Cooperativa de Pesquisa Norte/Nordeste do Gás Natural RECOGÁS-N/NE, presente no Instituto de Energia Sustentável (IES) da Universidade Federal da Paraíba. Tal unidade possui uma estrutura de aço carbono, utilizando uma tubulação de aço inoxidável. Um dos objetivos do estudo visa uma aproximação dos resultados obtidos experimentalmente neste estudo com os resultados obtidos teoricamente por SANTOS (2005). Para efeito de validação, foi utilizado o software Engineering Equation Solver (EES) para a obtenção das propriedades, principalmente as inerentes ao fluido de trabalho, utilizando-se dados de entrada obtidos experimentalmente. Ainda visa-se expor aspectos inerentes e exclusivos de um trabalho essencialmente experimental, onde será abordada a metodologia experimental aplicada com o uso dos materiais utilizados, as discussões em relação aos aspectos construtivos e de funcionamento da unidade, problemas detectados, intervenções realizadas na unidade piloto e, por fim, a proposição de soluções de alguns dos problemas observados.

Submitted by RENNER AUGUSTO TOLÊDO CAMPOS null (renneraugustocampos@gmail.com) on 2017-05-12T23:46:36Z No. of bitstreams: 1 Dissertação de Renner Campos - engenharia mecanica.pdf: 2528183 bytes, checksum: 3649363ab3dc4c5005953cf561fd4c6c (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-05-16T13:35:46Z (GMT) No. of bitstreams: 1 campos_rat_me_ilha.pdf: 2528183 bytes, checksum: 3649363ab3dc4c5005953cf561fd4c6c (MD5) / Made available in DSpace on 2017-05-16T13:35:46Z (GMT). No. of bitstreams: 1 campos_rat_me_ilha.pdf: 2528183 bytes, checksum: 3649363ab3dc4c5005953cf561fd4c6c (MD5) Previous issue date: 2017-03-23 / Sistemas de refrigeração são indispensáveis para o modo de vida do homem atual, porém o grande gasto energético, de fontes não renováveis, e os impactos ambientais, levam-nos a estudar e a pensar em outras fontes de energia, de preferência renováveis, e em outros ciclos de refrigeração com gasto energético menor. Este trabalho tem como objetivo a modelagem de um sistema de refrigeração por absorção de vapor para o conforto térmico de ambientes, verificando a viabilidade desse sistema de refrigeração para aplicação em salas de aula. No presente trabalho mostra-se o sistema de refrigeração como sendo umas das alternativas ao sistema de refrigeração por compressão de vapor, o qual possui um alto gasto energético. Para o funcionamento do sistema de refrigeração por absorção de vapor foi proposto a energia solar como fonte de energia térmica do gerador, pois em regiões como Rio Verde – GO (localizada na região de latitude 17°47’S e longitude 50°58’W, onde o clima tropical predomina em quase todos os meses do ano, com temperatura mínima de ~20 ° C e máxima de ~30 °C) o condicionamento do ambiente é imprescindível. Foi utilizado o software EES para a simulação e modelagem do sistema de absorção de vapor, baseado nas trocas de calor entre os componentes desse sistema, desprezando perdas energéticas e de pressões que ocorrem em um ciclo real de absorção de vapor. As simulações e resultados mostraram que, nessa região tropical, o clima é propício para o uso de energia solar e que sua transformação em energia térmica é suficiente para o funcionamento do gerador de um ciclo de absorção de vapor, viabilizando o conforto térmico do ambiente a ser refrigerado. / Cooling systems are indispensable for today's man's way of life, but the high energy expenditure from non-renewable sources and environmental impacts lead us to study and think about other sources of energy, preferably renewable, and in other refrigeration cycles with lower energy expenditure. The objective of this work is the modeling of a vapor absorption refrigeration system for the thermal comfort of environments, verifying the viability of this refrigeration system for application in classrooms. In the present work is shown the refrigeration system as one of the alternatives to the system of refrigeration by compression of steam, which has high energy expenditure. For the operation of the vapor absorption refrigeration system, solar energy was proposed as the generator's thermal energy source, since in regions such as Rio Verde - GO (located in latitude 17° 47' S and longitude 50° 58' W, where the tropical climate prevails in almost every month of the year, with a minimum temperature of ~ 20° C and maximum of ~ 30° C), the ambient air-conditioning is essential. EES software was used for the simulation and modeling of the vapor absorption system based on the heat exchanges between the components of this system, disregarding energy and pressures losses that occur in a real vapor absorption cycle. The simulations and results showed that, in this tropical region, the climate is favorable to use solar energy and its transformation into thermal energy is sufficient for the operation of the generator of a vapor absorption cycle, allowing the thermal comfort of the environment.

Orientador: Silvia Azucena Nebra de Perez / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-11T16:10:36Z (GMT). No. of bitstreams: 1 PalaciosBereche_Reynaldo_M.pdf: 8960679 bytes, checksum: a6e8e552788d00fa0fb258923ebe13a9 (MD5) Previous issue date: 2008 / Resumo: Neste trabalho e feita uma revisão em relação à participação do gás natural na matriz energética mundial, brasileira e no Estado de São Paulo. Características do setor terciário, assim como da utilização do gás natural neste setor de consumo, são apresentadas também na primeira parte. Foi feita uma revisão das tecnologias de utilização de gás natural no setor terciário, assim como da tecnologia dos sistemas de refrigeração por absorção, das diferentes configurações do ciclo, e dos fluidos de trabalho utilizados neste tipo de sistema. Uma metodologia para o calculo da exergia da solução água brometo de lítio, comumente utilizada como fluido de trabalho em sistemas de refrigeração por absorção para condicionamento de ambientes, foi elaborada. Para a realização das analises exegética e exergoeconomica do sistema foi realizado o calculo da exergia total dos fluidos de trabalho considerando as parcelas de exergia química e física. A analise exegética compreendeu o calculo da irreversibilidade em cada componente do sistema assim como da total. Na ultima parte do trabalho foi realizada a analise termodinâmica, exegética e exergoeconomica do sistema de refrigeração por absorção de simples e duplo efeito H2O/LiBr, considerando como fontes de aquecimento um sistema de queima direta de gás natural e energia de rejeito de um sistema de cogeração. Os resultados são comparados e discutidos / Abstract: A review about the participation of the natural gas in the energetic matrix was done in this work, considering the scope international, Brazilian and the Sao Paulo State. Characteristics of the tertiary sector and the natural gas utilization in this consumption sector are also presented. A review about the technologies of utilization of natural gas in the tertiary sector was also done. In the following part, the technology of absorption refrigeration systems, different configurations of the cycle and working fluids were reviewed. A methodology for the exergy calculation of the lithium bromide ¿ water solution was elaborated. The lithium bromide ¿ water solution is widely utilized as working fluid in absorption refrigeration system for air conditioning. The exergy calculation takes in account the chemical and physical parcel of the exergy, which is important to realize the exergetic and exergoeconomic analysis of the system. In the last part of the work it was done a thermodynamic, exergetic and exergoeconomic analysis of the absorption refrigeration system H2O/LiBr of single and double effect. The exergetic analysis included the irreversibility calculation in each component and the total irreversibility of the system. Two different energy sources were considered: direct heating through natural gas combustion and the utilization of rejected energy in a cogeneration system. The different results were compared. / Mestrado / Mestre em Planejamento de Sistemas Energéticos

Submitted by Rafael Santana (rafael.silvasantana@ufpe.br) on 2017-07-12T18:01:48Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Aida Avendano_Dissertacao_Eng Mecanica_UFPE.pdf: 2879829 bytes, checksum: 90b10e461eb8407986cea09be582a591 (MD5) / Made available in DSpace on 2017-07-12T18:01:48Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Aida Avendano_Dissertacao_Eng Mecanica_UFPE.pdf: 2879829 bytes, checksum: 90b10e461eb8407986cea09be582a591 (MD5) Previous issue date: 2016-01-29 / PRH-PB203 EQUIPAMENTOS/PETROBRAS / O processo de transferência de calor e massa dentro de um absorvedor tubular em espiral de Brometo de Lítio-Água (LiBr/H2O), resfriado com água em contracorrente, foi simulado usando um modelo matemático não linear. Para a simulação criou-se um programa em Matlab, usando o método numérico iterativo. Na calibração da malha física foram utilizadas condições de trabalho do absorvedor e o coeficiente de transferência de massa efetivo, Kef, obtidos da literatura. O coeficiente de transferência de calor global, U, foi calculado usando a resistência térmica global dentro do absorvedor. Para o cálculo do coeficiente de transferência de massa e de calor da interface solução-vapor se utilizaram correlações de analogia de transferência de calor e massa. As distribuições da temperatura e concentração da solução de LiBr/H2O, e a temperatura da água de resfriamento ao longo do comprimento do absorvedor foram determinadas utilizando o programa desenvolvido e os resultados obtidos apresentaram uma boa concordância quando comparados com dados reportados na literatura. Finalmente, foi analisada a influência da variação de alguns dos parâmetros, tais como temperatura e vazão de entrada da água de resfriamento, comprimento do absorvedor e material do tubo absorvedor dentro do absorvedor utilizando o programa desenvolvido. Os resultados obtidos mostraram que o programa desenvolvido permite predizer o comportamento do processo de transferência de massa e calor dentro do absorvedor em espiral de LiBr/H2O, além de representar uma ferramenta para o dimensionamento e/ou otimização deste componente. / The mass and heat transfer process in a spiral tubular absorber of the Water/Lithium Bromide (LiBr/H2O), cooled with in counter-current, was simulated using a nonlinear mathematical model. For the simulation was developed a program in Matlab, using the iterative numerical method. For the calibration of physical mesh were used absorber working condition and effective mass transfer coefficient, Kef, obtained from the literature. The global heat transfer coefficient, U, was calculated using the global thermal resistance within the absorber. For the calculation of the mass and heat transfer coefficient of the interface vapor-solution are used analogy correlations of mass and heat transfer. The temperature distribution and concentration of LiBr/H2O, and the cooling water temperature along of the length of the absorber were determined using the program developed, and the result obtained showed good agreement when compared to the data reported in the literature. Finally, the influence of the variation the some parameters were analyzed, such as inlet temperature and mass flow of cooling water, length of the absorber and material absorber tube within the absorber using the developed program. The result obtained showed that this program allowed to predict the behavior of the mass and heat transfer process in the absorber spiral of the LiBr/H2O, also represents a tool for the design and/or optimization of this component.