Avaliação da influência da composição da mistura zeotrópica R125 + R1234ze(E) no desempenho do ciclo de Rankine orgânico
Data
2022-12-13
Autores
Costa, Henrique Magyar [UNIFESP]
Orientadores
Silva, Luciana Yumi Akisawa [UNIFESP]
Tipo
Trabalho de conclusão de curso de graduação
Título da Revista
ISSN da Revista
Título de Volume
Resumo
O aumento no consumo de energia e o agravamento de problemas ambientais devido à queima de combustíveis fósseis tem incentivado a busca por novas fontes de energia que sejam mais limpas. O Ciclo de Rankine Orgânico (CRO) é um ciclo de geração de potência que utiliza compostos orgânicos como fluido de trabalho, e que tem despertado o interesse recentemente, por ser uma tecnologia promissora para converter fontes de calor de baixa temperatura (como radiação solar, energia geotérmica, combustão de biomassa ou calor residual de processos industriais) em trabalho útil ou eletricidade. O presente trabalho teve como objetivo simular e analisar o desempenho do Ciclo de Rankine Orgânico (CRO) utilizando uma mistura zeotrópica com os fluidos R125 + R1234ze(E) e avaliar a influência da composição da mistura no desempenho do CRO. As misturas zeotrópicas estão se tornando excelentes candidatas a serem utilizadas como fluido de trabalho, pois diferentemente das substâncias puras, elas apresentam um comportamento não isotérmico em processos de transição de fase, promovendo melhor o desempenho do CRO. As simulações foram realizadas no simulador livre DWSIM. A fim de comparações foi avaliado o desempenho do CRO por meio da eficiência térmica (η) e a razão de trabalho (bwr - “back work ratio”), pois quanto maior a eficiência térmica e menor bwr, melhor será o desempenho do ciclo de geração de potência. Dessa forma os resultados mostraram que a eficiência térmica do CRO aumenta conforme o aumento da fração molar do R1234ze(E), e atinge o seu máximo utilizando esse fluido como substância pura. Além desse aspecto, o R1234ze(E) possui um menor impacto ambiental em relação ao R125 e, portanto, é mais vantajoso a utilização deste como fluido de trabalho. Todavia, o resultado obtido não foi o esperado, pois acreditava-se que a eficiência térmica no CRO utilizando uma mistura zeotrópica seria maior em relação ao da substância pura. Acredita-se que este comportamento se deve as condições de operação, e principalmente, ao impacto da temperatura do evaporador na eficiência do ciclo.
The increase in energy consumption and the aggravation of environmental problems due to the burning of fossil fuels has encouraged the search for new energy sources that are cleaner. The Organic Rankine Cycle (ORC) is a power generation cycle that uses organic compounds as working fluid, and that has recently aroused interest, as a promising technology to convert low temperature heat sources (such as solar radiation, geothermal energy, biomass combustion or waste heat from industrial processes) into useful work or electricity. This work aimed to simulate and analyze the performance of the Organic Rankine Cycle (ORC) using a zeotropic mixture with the fluids R125 + R1234ze(E) and to evaluate the influence of the composition of the mixture on the performance of the ORC. Zeotropic mixtures are becoming excellent candidates to be used as a working fluid, because unlike pure substances, they present a nonisothermal behavior in phase transition processes, promoting better ORC performance. The simulations were performed in the free DWSIM simulator. For comparison purposes, the performance of the ORC was evaluated through thermal efficiency (η) and the work ratio (bwr " back work ratio"), since the greater the thermal efficiency and the lower bwr, the better the performance of the power generation cycle. Thus, the results showed that the thermal efficiency of ORC increases as the molar fraction of R1234ze(E) increases and reaches its maximum using this fluid as a pure substance. In addition to this aspect, R1234ze(E) has a lower environmental impact compared to R125 and, therefore, it is more advantageous to use it as a working fluid. However, the result obtained was not what was expected, as it was believed that the thermal efficiency in ORC using a zeotropic mixture would be greater than that of the pure substance. It is believed that this behavior is due to the operating conditions, and mainly, to the impact of the evaporator temperature on the efficiency of the cycle.
The increase in energy consumption and the aggravation of environmental problems due to the burning of fossil fuels has encouraged the search for new energy sources that are cleaner. The Organic Rankine Cycle (ORC) is a power generation cycle that uses organic compounds as working fluid, and that has recently aroused interest, as a promising technology to convert low temperature heat sources (such as solar radiation, geothermal energy, biomass combustion or waste heat from industrial processes) into useful work or electricity. This work aimed to simulate and analyze the performance of the Organic Rankine Cycle (ORC) using a zeotropic mixture with the fluids R125 + R1234ze(E) and to evaluate the influence of the composition of the mixture on the performance of the ORC. Zeotropic mixtures are becoming excellent candidates to be used as a working fluid, because unlike pure substances, they present a nonisothermal behavior in phase transition processes, promoting better ORC performance. The simulations were performed in the free DWSIM simulator. For comparison purposes, the performance of the ORC was evaluated through thermal efficiency (η) and the work ratio (bwr " back work ratio"), since the greater the thermal efficiency and the lower bwr, the better the performance of the power generation cycle. Thus, the results showed that the thermal efficiency of ORC increases as the molar fraction of R1234ze(E) increases and reaches its maximum using this fluid as a pure substance. In addition to this aspect, R1234ze(E) has a lower environmental impact compared to R125 and, therefore, it is more advantageous to use it as a working fluid. However, the result obtained was not what was expected, as it was believed that the thermal efficiency in ORC using a zeotropic mixture would be greater than that of the pure substance. It is believed that this behavior is due to the operating conditions, and mainly, to the impact of the evaporator temperature on the efficiency of the cycle.