Effects of inlet subcooling on the flow boiling heat transfer performance of bi-porous mini-channels

Abstract

Micro/mini-channel heat sinks have been viewed to be a potential option for the heat removal of electronics with rising thermal flux. A bi-porous mini-channel, fabricated through sintering copper woven tapes on channel surfaces, is developed in this paper for the sake of improving the flow boiling heat transfer. Two different pore structures exist in the copper woven tape: one is cavity constituted via copper strands, another one is crevice constituted via copper wires. The bi-porous mini-channel is multi-channel type, and the dimension of each single channel is 1.2 × 1.5 mm. Experimental studies,with various inlet subcoolings of 10.7, 13.7 and 16.7 °C, on the flow boiling performance of the bi-porous mini-channel were conducted, and a traditional mini-channel possessing planar surfaces was employed for comparison experiments. Working fluid R141b, inlet mass flux at 255 kg/m2·s and outlet pressure at 50 kPa (gage pressure) are adopted in the experiments. Boiling curve, heat transfer coefficient, temperature distribution and performance evaluation were investigated, combining with the visualization of bubble behaviors. The result demonstrates that the bi-porous mini-channel triggers the onset of nucleate boiling in the case of smaller heat flux conditions than the mini-channel with planar surface under different inlet subcoolings. The boiling hysteresis phenomenon is more obvious at higher subcooling for the mini-channel with planar surface, but it is eliminated in the bi-porous mini-channel under the same conditions. Under high heat flux conditions, the obvious inlet backflow phenomenon is observed and may deteriorate the heat transfer performance. The present study indicates that the bi-porous mini-channel possesses high heat transfer performance and temperature uniformity, which may meet the high demands of thermal management in fields such as battery cooling of electric vehicles.