An experimental study of the effects of porosity and ratio of fin to channel width on water flow boiling in copper foam fin microchannels

Abstract

Flow boiling in copper foam fin microchannels (FFMC) has demonstrated better heat transfer performance and flow stability. In this work, systematic experiments are conducted to investigate the effects of structural parameters on flow boiling in five FFMCs with porosities ranging from 0.78 to 0.82 and ratios of fin width to channel width ranging from 0.5 to 2. Five mass fluxes ranging from 68 kg/(m2s) to 408 kg/(m2s) and effective heat fluxes ranging from 2 W/cm2 to 297 W/cm2 are tested. The heat transfer, pressure drop, and flow instability characteristics are analyzed. Generally, the heat transfer in FFMCs follows the “three-zone” model. The heat transfer coefficient first increases with increasing heat flux and then decreases. A “synchronous backflow” phenomenon is observed in FFMCs, which is the direct cause of heat transfer deterioration. Due to the interaction of heat transfer area and the transverse flow resistance through the fins, the heat transfer coefficient increases with decreasing porosity in the low-quality region, while the opposite trend is observed in the high-quality region. The utilization efficiency of the fin area decreases as the fin width increases. An optimal ratio of fin width to channel width exists corresponding to the best heat transfer performance, which equals one in this work. A correlation is developed based on 583 data points considering heat transfer mechanisms in channels and fins. The new correlation predicts the experimental values with a mean absolute percentage error of 9 %, and over 99 % of the data are predicted within a 30 % deviation. A performance evaluation criterion is defined to comprehensively compare the FFMCs, and the FFMC with the porosity of 0.78 demonstrates the best flow boiling performance due to higher heat transfer coefficients and lower pumping powers when the ratio of fin to channel width is equal to one.