Avaliação de vazamentos internos em expansores scroll com o uso de simulação CFD
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Citações na Scopus
Tipo de produção
Dissertação
Data
2017
Autores
Oliveira, F. V.
Orientador
Mello, Paulo Eduardo Batista de
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Texto completo (DOI)
Palavras-chave
Expansor Scroll,Energia,Fontes alternativas,Scroll expander,CFD,Internal leakages,Tangential clearance,Pressure ratio,Vazamentos internos,Folga tangencial,Razão de pressão
Resumo
A geração de energia distribuída tem se tornado uma alternativa interessante para o fornecimento de energia ao economizar investimentos em linha de transmissão e reduzir as perdas. O aproveitamento de fontes de calor de baixa temperatura, geralmente rejeitadas ao meio ambiente, e a utilização da energia proveniente de fontes renováveis surgem como possíveis aplicações. Nesse contexto, a seleção do expansor (ou turbina) que deve apresentar
uma alta eficiência isentrópica para otimizar a geração de energia requer uma atenção especial. Para aplicações de baixa potência (1 kW até 10 kW), o expansor scroll é o mais recomendado, de acordo com trabalhos recentes. Estudos anteriores mostram que os vazamentos internos são as principais fontes de ineficiência desse tipo de máquina. Embora o desempenho do expansor possa ser caracterizado pelo fator de preenchimento e eficiência isentrópica, não é comum observar tais resultados em pesquisas na área de simulação numérica, juntamente com a validação. Neste trabalho é estudado o efeito dos vazamentos internos sobre o desempenho de um expansor scroll ao realizar simulações transientes do escoamento compressível utilizando a Fluidodinâmica Computacional (CFD). A potência
gerada, o fator de preenchimento e a eficiência isentrópica são obtidos e comparados com os resultados experimentais do grupo de pesquisa. Foi verificado que o fator de preenchimento não se altera com a variação da razão de pressão, ou seja, os vazamentos internos permanecem praticamente constantes com o aumento da pressão de entrada. O aumento da folga tangencial reduz o valor da razão de pressão onde é observada a máxima eficiência isentrópica. Se comparado aos valores experimentais, as simulações mostraram potência gerada 22% superior e fluxo de massa 20% inferior. Os valores de potência são bastante satisfatórios e essa diferença pode ser atribuída ao atrito presente na máquina real. O desvio no fluxo de massa leva a concluir que no experimento estavam ocorrendo vazamentos de
topo, não considerados nas simulações numéricas
Distributed power generation has become an interesting alternative to energy supply by saving investments in transmission line and reducing losses. The use of low heat sources usually rejected to the environment and the energy utilization from renewable sources, arise as possible applications. Within this context, the expander selection – which should present as high isentropic efficiency as possible to optimize the power generation – requires a special attention. For low power applications, between 1 kW by 10 kW, the scroll expander is the most recommended, according to recent works. Previous studies show that internal leakages are the mainly sources of inefficiency on this type of machine. Although the expander performance can be characterized by the filling factor and isentropic efficiency, it is not common to see these results in numerical simulation researches, together with the validation. In this work the effects of internal leakages on the expander performance are studied when performing transient simulations of the compressible flow using Computational Fluid Dynamics (CFD). The generated power, filling factor and isentropic efficiency are obtained and compared with experimental results from the research group. It was verified that the filling factor does not change with the pressure rate variation, therefore the internal leakages remain practically constants with the inlet pressure increase. The increase in tangential clearance reduces the pressure ratio value where the highest isentropic efficiency is observed. If compared with experimental results, the simulations have shown generated power 22% higher and mass flow 20% lower. The power values are quite satisfactory and this difference can be attributed to the friction losses present in the real machine. The mass flow deviation indicates that radial leakages were occurring on the experiment, which are not considered in the numerical simulations
Distributed power generation has become an interesting alternative to energy supply by saving investments in transmission line and reducing losses. The use of low heat sources usually rejected to the environment and the energy utilization from renewable sources, arise as possible applications. Within this context, the expander selection – which should present as high isentropic efficiency as possible to optimize the power generation – requires a special attention. For low power applications, between 1 kW by 10 kW, the scroll expander is the most recommended, according to recent works. Previous studies show that internal leakages are the mainly sources of inefficiency on this type of machine. Although the expander performance can be characterized by the filling factor and isentropic efficiency, it is not common to see these results in numerical simulation researches, together with the validation. In this work the effects of internal leakages on the expander performance are studied when performing transient simulations of the compressible flow using Computational Fluid Dynamics (CFD). The generated power, filling factor and isentropic efficiency are obtained and compared with experimental results from the research group. It was verified that the filling factor does not change with the pressure rate variation, therefore the internal leakages remain practically constants with the inlet pressure increase. The increase in tangential clearance reduces the pressure ratio value where the highest isentropic efficiency is observed. If compared with experimental results, the simulations have shown generated power 22% higher and mass flow 20% lower. The power values are quite satisfactory and this difference can be attributed to the friction losses present in the real machine. The mass flow deviation indicates that radial leakages were occurring on the experiment, which are not considered in the numerical simulations