Comportamento térmico e hidrodinâmico da ebulição convectiva do HFE-7100 em microdissipador de calor baseado em microcanais
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Data
2019-11-29
Autores
Zago, João Vitor
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Universidade Estadual Paulista (Unesp)
Resumo
Dissipadores de calor compactos, baseados em microcanais, têm se mostrado um meio eficaz para o resfriamento de dispositivos de alta densidade de energia, tais como microprocessadores, além de proporcionarem redução de material utilizado para a fabri-cação e do inventário de fluido refrigerante necessário. Sistemas bifásicos que operam com fluidos refrigerantes proporcionam coeficientes de transferência de calor elevados para baixos valores de velocidade mássica e uma distribuição de temperatura mais uni-forme na superfície. O presente estudo teve por objetivo avaliar experimentalmente o desempenho de um dissipador de calor baseado em microcanais, em condições de ebuli-ção convectiva saturada do fluido HFE-7100. O dissipador, em cobre eletrolítico, possui 33 microcanais de seção retangular com dimensões de 10 mm de comprimento, 200 μm de largura, 500 μm de altura e espaçados 100 μm entre si. A eficiência térmica do dissi-pador foi avaliada utilizando como fluido de trabalho o HFE-7100 (fluido refrigerante com baixo ozone depleting potencial, ODP, e global warming potential, GWP). Dados experimentais para o coeficiente de transferência de calor (CTC) e perda de pressão fo-ram obtidos em condições de escoamento monofásico e bifásico saturados, para diferen-tes valores de velocidades mássicas. As condições testadas foram de fluxo de calor im-posto (footprint) variando de 50 a 700 kW/m², com velocidades mássicas do fluido entre 392 e 875 kg/m²s, obtendo coeficientes de transferência de calor (CTC) de até 60 kW/m²K e quedas de pressões de até 12 kPa. Notou-se um aumento no CTC com a di-minuição do subresfriamento de entrada e da velocidade mássica; notou-se também um aumento da queda de pressão com um aumento da velocidade mássica e com a diminui-ção do subresfriamento de entrada. As correlações que melhor predisseram o CTC na região bifásica foram a de Liu e Wu (2010) e Kim e Mudawar (2013), com aproximada-mente 91% e 84% dos dados previstos com erro menores que 30%, respectivamente; para a queda de pressão na região bifásica as correlações de Zhang et al. (2010) e Kim e Mudawar (2012) apresentaram 58,3% dos dados previstos com erro na faixa de ±30%.
Microchannel-based heat sinks have been shown to be an effective way of cool-ing high-density energy devices such as microprocessors, as well as reducing the material used to manufacture the exchangers and the required refrigerant inventory. Two-phase flow systems that operate with refrigerant fluids provide high heat transfer coefficients with low mass flux values and more uniform temperature distribution on the surface. The present study aimed to evaluate experimentally the performance of a heat sink based on microchannels under saturated conditions of convective boiling of HFE-7100 fluid. The analyzed heat sink has 33 rectangular section microchannels measuring 10 mm length, 200 μm wide, 500 μm high and spaced 100 μm apart. The heat sink was evaluat-ed using HFE-7100 (low ozone-depleting potential, ODP, and global warming potential, GWP) as working fluid. Experimental data for the heat transfer coefficient and pressure drop were obtained under saturated single and two-phase flow conditions for different values of mass velocities. An experimental apparatus was assembled and validated for the accomplishment of testing. As experimental conditions, the heat flux was applied in a range from 50 to 700 kW/m², with mass flux from 392 and 875 kg/m²s, obtaining a heat transfer coefficient of 60 kW/m² and pressure drop up to 12 kPa. By decreasing the mass flux and the input of the subcooling the HTC increases; the pressure drop increases monotonically with the increase in the mass flux and the decrease in the subcooling at the inlet. The correlations of Liu and Wu (2010) and Kim and Mudawar (2013), for HTC in two-phase flow, predicted 91% and 84% of the data within the ±30% error bands, respectively; for the pressure drop, the correlations of Zhang et al. (2010) and Kim and Mudawar (2012) predicted 58.3% of data with error within ± 30%.
Microchannel-based heat sinks have been shown to be an effective way of cool-ing high-density energy devices such as microprocessors, as well as reducing the material used to manufacture the exchangers and the required refrigerant inventory. Two-phase flow systems that operate with refrigerant fluids provide high heat transfer coefficients with low mass flux values and more uniform temperature distribution on the surface. The present study aimed to evaluate experimentally the performance of a heat sink based on microchannels under saturated conditions of convective boiling of HFE-7100 fluid. The analyzed heat sink has 33 rectangular section microchannels measuring 10 mm length, 200 μm wide, 500 μm high and spaced 100 μm apart. The heat sink was evaluat-ed using HFE-7100 (low ozone-depleting potential, ODP, and global warming potential, GWP) as working fluid. Experimental data for the heat transfer coefficient and pressure drop were obtained under saturated single and two-phase flow conditions for different values of mass velocities. An experimental apparatus was assembled and validated for the accomplishment of testing. As experimental conditions, the heat flux was applied in a range from 50 to 700 kW/m², with mass flux from 392 and 875 kg/m²s, obtaining a heat transfer coefficient of 60 kW/m² and pressure drop up to 12 kPa. By decreasing the mass flux and the input of the subcooling the HTC increases; the pressure drop increases monotonically with the increase in the mass flux and the decrease in the subcooling at the inlet. The correlations of Liu and Wu (2010) and Kim and Mudawar (2013), for HTC in two-phase flow, predicted 91% and 84% of the data within the ±30% error bands, respectively; for the pressure drop, the correlations of Zhang et al. (2010) and Kim and Mudawar (2012) predicted 58.3% of data with error within ± 30%.
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Palavras-chave
Hfe-7100, Ebulição convectiva, Microcanais, Queda de pressão, Coeficiente de transferência de calor, Convective boiling, Microchannels, Pressure drop, Heat transfer coefficient