Intensificação da transferência de calor em trocadores de calor compactos com aletas onduladas assimétricas
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Data
2022-08-24
Autores
Mattoso, Paulo Jorge Gonçalves da Silva
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Universidade Estadual Paulista (Unesp)
Resumo
Devido ao elevado crescimento industrial, aumentou-se a necessidade do desenvolvimento de equipamentos mais eficientes, dos quais os trocadores de calor se destacam. Por causa da alta demanda desses dispositivos, é evidente a necessidade de contínuos estudos que avaliem oportunidades tecnológicas para aumentar o desempenho termo-hidráulico dos trocadores de calor, portanto, o presente trabalho avalia a intensificação da transferência de calor em um trocador de calor compacto com a combinação de técnicas passivas, a partir de aletas onduladas assimétricas aplicado a sistemas de refrigeração e climatização de ambientes. Será considerado para a abordagem computacional um modelo tridimensional, escoamento incompressível, regime estacionário e turbulento. O trocador de calor compacto terá a inserção de tubos, variando sua configuração entre tubos circulares, elípticos e mistos, seguindo um arranjo desalinhado. A perda de carga é avaliada pelo fator de atrito (f) e a transferência de calor pelo fator de Colburn (j). A comparação dos modelos assimétricos foi feita em relação a um trocador de calor com aletas onduladas simétricas. Os resultados mostraram um aumento de 3,71% do fator de Colburn no modelo com razão assimétrica < 1 para 〖Re〗_((L/H) ) = 264. O modelo com razão assimétrica > 1 apresentou uma redução no fator de Colburn (j) de 1,72%, uma diminuição no fator de atrito (f) de 9,10% e consequentemente um aumento no desempenho termo-hidráulico de 8,12%, para 〖Re〗_((L/H) )=132. No geral, as razões assimétricas tem um maior impacto na queda de pressão do que na transferência de calor, no qual o modelo R_L=1,2 permite um melhor custo-benefício para a indústria devido a seu bom desempenho termo-hidráulico em relação ao modelo padrão.
Due to the high industrial growth, the need for the development of more efficient equipment has increased, of which the heat exchangers stand out. Because of the high demand of these devices, it is evident the need for continuous studies that evaluate technological opportunities to increase the thermo-hydraulic performance of heat exchangers, therefore, the present work evaluates the heat transfer enhancement in a compact heat exchanger with the combination of passive techniques, using asymmetrical wavy fins within the operational Reynolds number range of air cooling and air conditioning systems. A three-dimensional model, incompressible flow and steady and turbulent regime will be considered for the computational modeling. The compact heat exchanger will have the insertion of tubes, varying its configuration between circular, elliptical and mixed tubes, following a staggered arrangement. The pressure drop is evaluated by the friction factor (f) and the heat transfer by the Colburn factor (j). The comparison of the asymmetric models was made in relation to a heat exchanger with standard wavy fins, with fixed wavelengths. The results showed a 3,71% increase of the Colburn factor in the model with asymmetric ratio < 1, for 〖Re〗_((L/H) )=264 . The model with asymmetric ratio > 1 showed a decrease in Colburn fator (j) of 1,72%, a decrease in friction fator (f) of 9,10% and consequently an increase in thermo-hydraulic performance of 8,12% for 〖Re〗_((L/H) )=132. Overall, the asymmetric ratios have a greater impact on pressure drop than on heat transfer, in which the R_L=1,2 model allows a better cost-benefit for the industry due to its good thermo-hydraulic performance compared to the standard model.
Due to the high industrial growth, the need for the development of more efficient equipment has increased, of which the heat exchangers stand out. Because of the high demand of these devices, it is evident the need for continuous studies that evaluate technological opportunities to increase the thermo-hydraulic performance of heat exchangers, therefore, the present work evaluates the heat transfer enhancement in a compact heat exchanger with the combination of passive techniques, using asymmetrical wavy fins within the operational Reynolds number range of air cooling and air conditioning systems. A three-dimensional model, incompressible flow and steady and turbulent regime will be considered for the computational modeling. The compact heat exchanger will have the insertion of tubes, varying its configuration between circular, elliptical and mixed tubes, following a staggered arrangement. The pressure drop is evaluated by the friction factor (f) and the heat transfer by the Colburn factor (j). The comparison of the asymmetric models was made in relation to a heat exchanger with standard wavy fins, with fixed wavelengths. The results showed a 3,71% increase of the Colburn factor in the model with asymmetric ratio < 1, for 〖Re〗_((L/H) )=264 . The model with asymmetric ratio > 1 showed a decrease in Colburn fator (j) of 1,72%, a decrease in friction fator (f) of 9,10% and consequently an increase in thermo-hydraulic performance of 8,12% for 〖Re〗_((L/H) )=132. Overall, the asymmetric ratios have a greater impact on pressure drop than on heat transfer, in which the R_L=1,2 model allows a better cost-benefit for the industry due to its good thermo-hydraulic performance compared to the standard model.
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Palavras-chave
Aleta ondulada assimétrica, Simulação numérica, Intensificação da transferência de calor, Trocador de calor compacto, Técnicas passivas, Asymmetric wavy fin, Numerical simulation, Heat transfer enhancement, Compact heat exchangers, Passive techniques