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Análise experimental de sistemas de refrigeração operando com R-290 e R-600a como fluidos refrigerantes alternativosde Castro Silva, José 31 January 2008 (has links)
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Previous issue date: 2008 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os refrigerantes CFCs (clorofluorcarbonos) como o R-12, foram identificados como de alto
poder destruidor da camada de ozônio que protege a superfície da terra, devido à presença de
cloro em sua estrutura. Os HCFCs (hidroclorofluorcarbonos) como o R-22, por possuírem cloro
em sua estrutura, também devem ser substituídos como fluidos refrigerantes. Na Europa,
equipamentos novos não são produzidos com o HCFC-22, desde dezembro de 2003. Diante da
necessidade de substituição desses gases nocivos ao planeta, os hidrocarbonetos (HC)
apresentam-se como bons candidatos a fluidos refrigerantes alternativos, pela ausência de
átomos de cloro em sua estrutura e por não destruírem a camada de ozônio. Esses fatos, aliados a
um baixo potencial de causar aquecimento global, fazem dos hidrocarbonetos bons candidatos ao
uso em sistemas de refrigeração. Como contribuição a esse tema, a presente dissertação analisa
experimentalmente os sistemas de refrigeração por compressão a vapor de um bebedouro e de
uma câmara frigorífica, representantes das classes de refrigeração doméstica e comercial, ambas
de pequeno porte. Os sistemas estudados foram testados com os fluidos refrigerantes
(hidrocarbonetos): propano (R-290),isobutano (R-600a) e uma mistura de ambos em substituição
aos fluidos originais dos sistemas testados, o R-22 e o R-12.
Todos os testes foram realizados em condições normais de operação. Os resultados
experimentais indicam que a mistura propano e isobutano mostra-se como a melhor opção como
fluido alternativo em sistemas de refrigeração de pequeno porte utilizadores do R-12 ou R-22.
Em segundo lugar apresentou-se o R-600a. Na comparação individual, o R-600a mostrou-se
como a melhor opção para sistemas de refrigeração de pequeno porte ao invés do R-290. Porém,
para sistemas de médio porte originalmente projetados para R-22, o R-290 aparece como a
melhor opção
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<b>Exploratory Study on Advanced Heat Pump Water Heaters for Building Electrification and Decarbonization</b>Mridul Brijmohan Rathi (19195645) 24 July 2024 (has links)
<p dir="ltr">Energy consciousness initiatives have seen a recent uptick to curb the ever growing concerns of global warming. Heat Pumps are a crucial piece of technology for these efforts, as they consume lower energy than the requirement they satisfy and are typically used for refrigeration and HVAC systems. Hybrid Heat Pump Water Heater (HPWH) technologies have seen increased adoption, and the improvement of these technologies could pay dividends in the long run. </p><p dir="ltr">This project explores the optimal design space of HPWHs within the context of the Department of Energy Guidelines for their performance rating and compares several up and coming refrigerants with lower GWP than the current market dominant refrigerant, R-134a, to provide consistent performance with improvements on the environmental front along with potential cost improvements on the manufacturing front. For this purpose, Dymola, a simulation software that employs the Modelica language for modeling complex dynamic systems, is employed to study the transient behavior of a market example Heat Pump Water Heater. </p><p dir="ltr">The results of these simulations were validated using experimental data gathered in the laboratory using relevant instrumentation on the physical device and manufacture specified performance ratings to compare the validity of the simulation results. The results of the study indicated the presence of a multi-dimensional design space with a defined set of possible combinations for device implementation. Within that feasible region, there exist multiple trajectories of iso-preference which alter the overall device performance, and the careful study of these parameters and their implications on the device performance can lead to a more robust design pathway for future improvements of the device. The work also contextualizes these improvements by quantifying the relative importance of different parameters upon the final performance of the device, showing how to identify which parameters to focus on when embarking upon an improvement journey. Additionally, preliminarily ideal specifications for the device operation under different refrigerants studied were also identified to provide similar or better performance to the current device. </p><p dir="ltr">The study showed that when matching mass flux rates, R-152a, R-290, and R-600a outperform R-134a in terms of expected COP. Of the 3, only R-290 uses a smaller compressor size than the baseline R-134a cycle for achieving the required heating capacity. The other refrigerants studied do not improve upon the COP of the cycle, but do have benefits over R-134a in terms of their respective GWPs. </p><p dir="ltr">The results suggest that with the considered alterations, R-290 systems within the current charge restrictions (<150g) can be developed and achieve the same heating performance with slight improvements on COP and therefore potentially UEF values. </p><p dir="ltr">The study also shows that all refrigerants considered could achieve the required heating capacity with a considerably downsized condenser and appropriately reduced subcooling. It highlighted the trends being consistent across refrigerants and implemented a final alternative refrigerant through the identified optimization steps to arrive at a new configuration without revalidating the trends, showing that newer optimal configurations could be identified with minimal time spent in the simulation environment. </p><p dir="ltr">Finally, the study explored alternative control possibilities by way of overheating the water beyond its required setpoint and enabling a control based mixing at the outlet to reduce the energized time of the device and leveraging the exceptional insulation capabilities for thermal storage.</p>
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