Intensificação da transferência de calor em um trocador de calor compacto com dimples
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Data
2022-07-26
Autores
Ferreira, Cassiano Victor de Souza
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Os trocadores de calor são usados amplamente em aplicações industriais e cotidianas, podendo ser aplicados em diversos projetos de engenharia. Neste projeto foi estudado uma das principais formas de aprimorar estes dispositivos. Uma técnica de intensificação de transferência de calor passiva chamada dimples. Estes dispositivos geram estruturas de vórtices longitudinais e promovem o aumento da transferência térmica. Neste trabalho, um trocador de calor compacto com dimples foi analisado, considerando modelos com dimples alinhados e intercalados variando-se seus diâmetros de 0,8 mm, 1,2 mm e 1,4 mm, para tubos circulares e intercalados. Uma abordagem numérica tridimensional foi adotada, considerando um escoamento turbulento e em regime estacionário, para a faixa de Reynolds entre 500 e 4000, que compreende diversas aplicações em sistemas de refrigeração. As análises quanto a transferência de calor e a perda de carga no trocador de calor em função das alterações geométricas e operacionais são feitas através dos parâmetros termo-hidráulicos fator de Colburn (j) e fator de atrito (f). Os resultados mostraram que os modelos Alinhados para este caso tiveram vantagens em relação aos Intercalados, tanto na intensificação da transferência de calor quanto na eficiência global. O modelo Intercalados 2 se destacou devido a um elevado aumento do fator de Colburn de 43,3% junto a uma moderada penalização por perda de carga, chegando a um desempenho de 19%. O modelo Alinhados 3 também foi um destaque devido a seu elevado aumento da transferência de calor comparado ao caso base chegando a 48,8%. A análise realizada concluiu que, a medida em que o diâmetro dos dimples aumentaram, a transferência térmica e a perda de carga também aumentaram. Foi realizado também uma análise dos campos de temperatura e streamlines, verificando a formação de estrutura de vórtices e distorção das linhas de correntes nas concavidades dos dimples, que foram responsáveis pela intensificação da transferência de calor. Também foi observado pelos campos de velocidade uma redução da região de esteira, atrás do primeiro tubo do domínio, sendo responsável por auxiliar na troca de calor.
Heat exchangers are widely used in industrial and everyday applications and can be applied in various engineering projects. One of the main passive techniques of heat one of the main passive techniques of heat transfer enhancement are the dimples, which generate longitudinal vortex structures and promote the increase of heat transfer. In this work, a compact heat exchanger with dimples was analyzed, considering models with diameters of 0.8 mm, 1.2 mm and 1.4 mm, for circular and interleaved tubes. A three-dimensional numerical approach was adopted, considering turbulent and steady-state flow, for the Reynolds range between 500 and 4000, which comprises several applications in refrigeration systems. The analyzes regarding the heat transfer and the pressure loss in the heat exchanger as a function of the geometric and operational changes are made through the thermo-hydraulic parameters Colburn factor (j) and friction factor (f). The results showed that the aligned models for this case had advantages over the Interleaved ones, both in terms of intensification of heat exchange and global efficiency. The Aligned 2 model stood out due to a high Colburn factor increase of 44.1% with a low pressure drop penalty, reaching a performance increase of 19%. The Aligned 3 model was also a highlight due to its high increase in heat transfer compared to the base case, reaching 48.8% of performance increasing. It was analyzed that as the diameter of the dimples increased, the heat transfer and pressure drop also increased. An analysis of the temperature fields and streamlines was also carried out, verifying the formation of vortex structure and distortion of the current lines in the dimples concavities, which were responsible for the intensification of heat transfer. It was also observed by the velocity fields a reduction of the wake region, behind the first tube of the domain, being responsible for helping in the heat exchange.
Heat exchangers are widely used in industrial and everyday applications and can be applied in various engineering projects. One of the main passive techniques of heat one of the main passive techniques of heat transfer enhancement are the dimples, which generate longitudinal vortex structures and promote the increase of heat transfer. In this work, a compact heat exchanger with dimples was analyzed, considering models with diameters of 0.8 mm, 1.2 mm and 1.4 mm, for circular and interleaved tubes. A three-dimensional numerical approach was adopted, considering turbulent and steady-state flow, for the Reynolds range between 500 and 4000, which comprises several applications in refrigeration systems. The analyzes regarding the heat transfer and the pressure loss in the heat exchanger as a function of the geometric and operational changes are made through the thermo-hydraulic parameters Colburn factor (j) and friction factor (f). The results showed that the aligned models for this case had advantages over the Interleaved ones, both in terms of intensification of heat exchange and global efficiency. The Aligned 2 model stood out due to a high Colburn factor increase of 44.1% with a low pressure drop penalty, reaching a performance increase of 19%. The Aligned 3 model was also a highlight due to its high increase in heat transfer compared to the base case, reaching 48.8% of performance increasing. It was analyzed that as the diameter of the dimples increased, the heat transfer and pressure drop also increased. An analysis of the temperature fields and streamlines was also carried out, verifying the formation of vortex structure and distortion of the current lines in the dimples concavities, which were responsible for the intensification of heat transfer. It was also observed by the velocity fields a reduction of the wake region, behind the first tube of the domain, being responsible for helping in the heat exchange.
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Palavras-chave
Trocadores de Calor Compactos, Dimples, Simulação Numérica, Intensificação da transferência de calor., Compact Heat Exchangers, Numerical Simulation, Intensification of heat transfer