Análise do desempenho de condensadores de parede-aquecida usando um modelo distribuído
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Data
2020-01-27
Autores
Quizzini Junior, Gilmar Donizete
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
Nesse trabalho apresenta-se um modelo para analisar os condensadores do tipo parede-aquecida (hot-wall) usados em refrigeradores domésticos. Neste modelo, considera-se o escoamento do fluido refrigerante no interior do tubo do condensador e a transferência de calor entre a placa do revestimento externo do refrigerador, parede aquecida, e o ambiente externo. No modelo inclui-se também a transferência de calor entre a fita adesiva de alumínio, usada para a fixação do tubo na placa de revestimento externo e a transferência de calor, através do isolamento térmico, para o interior do refrigerador. O escoamento do fluido refrigerante é considerado unidimensional e dividido em três regiões: região monofásica de vapor superaquecido, região bifásica líquido-vapor e região monofásica de líquido sub-resfriado. O escoamento bifásico é analisado segundo o modelo homogêneo, ou seja, considerando o equilíbrio fluidodinâmico e térmico entre as fases. As equações do escoamento do fluido refrigerante, equação de conservação da massa, equação da quantidade de movimento linear e equação de conservação de energia, são resolvidas numericamente usando-se o Método de Volumes Finitos. As equações de conservação de energia ao longo da fita de alumínio e da parede aquecida também são resolvidas numericamente usando-se o Método de Volumes Finitos. O sistema de equações algébricas resultante é resolvido por substituições sucessivas e o modelo é validado comparando-se os resultados obtidos com dados experimentais disponíveis na literatura. Considerando a faixa de vazão em massa do fluido refrigerante isobutano, R600a, de 1,24 a 1,62 kg/h, o desvio relativo médio entre os resultados calculados e os dados experimentais de capacidade do condensador foi de 0,9%.
This work presents a model for the analysis of hot-wall condensers used in domestic refrigerators. The flow of refrigerant inside the condenser tube and the heat transfer between the outer coating plate of the refrigerator and the ambient air are considered. The heat transfer along the aluminum tape, used to hold the tube to the outer coating plate, and the heat transfer through the thermal insulation into the refrigerated compartment are also included in this model. The flow inside the tube is taken as one-dimensional and divided into three regions: superheated vapor region, two-phase liquid-vapor region and sub-cooled liquid region. The two-phase flow is analyzed according to the homogeneous model, i.e., considering conditions of thermal and hydrodynamic equilibrium between the phases. The equations of the refrigerant flow, mass conservation, momentum and energy conservation, are solved by the Finite Volume method. The equations of the energy conservation along the aluminum tape and the outer coating plate are also solved by the Finite Volume method. The set of algebraic equations, resulting from the discretization process of the differential equations, is solved iteratively by successive iterations, point-to-point along the condenser tube and the results obtained are compared with experimental data available in the literature. Considering the whole range of refrigerant mass flow rate analyzed, 1,24 to 1,62 kg/h, the mean relative deviation between the calculated results and the experimental of the condenser capacity data was 0,9 %.
This work presents a model for the analysis of hot-wall condensers used in domestic refrigerators. The flow of refrigerant inside the condenser tube and the heat transfer between the outer coating plate of the refrigerator and the ambient air are considered. The heat transfer along the aluminum tape, used to hold the tube to the outer coating plate, and the heat transfer through the thermal insulation into the refrigerated compartment are also included in this model. The flow inside the tube is taken as one-dimensional and divided into three regions: superheated vapor region, two-phase liquid-vapor region and sub-cooled liquid region. The two-phase flow is analyzed according to the homogeneous model, i.e., considering conditions of thermal and hydrodynamic equilibrium between the phases. The equations of the refrigerant flow, mass conservation, momentum and energy conservation, are solved by the Finite Volume method. The equations of the energy conservation along the aluminum tape and the outer coating plate are also solved by the Finite Volume method. The set of algebraic equations, resulting from the discretization process of the differential equations, is solved iteratively by successive iterations, point-to-point along the condenser tube and the results obtained are compared with experimental data available in the literature. Considering the whole range of refrigerant mass flow rate analyzed, 1,24 to 1,62 kg/h, the mean relative deviation between the calculated results and the experimental of the condenser capacity data was 0,9 %.
Descrição
Palavras-chave
Condensadores de parede-aquecida, Refrigerador doméstico, Análise de desempenho, Modelo distribuído, Hot-wall condenser, Domestic refrigerator, Performance analysis, Distributed model