Experimental investigation of flow boiling characteristics in counter-flow microchannels with different mass flux distributions

The cooling of high-power electronics urgently requires efficient and controllable heat dissipation techniques . In this work, a novel bidirectional counter-flow microchannels (CFMC) with mass flux distribution being regulated is proposed to achieve this goal. Flow boiling experiments are conducted in the CFMC and compared with traditional unidirectional parallel-flow microchannels (PFMC) by using deionized water as the working fluid. The effects of mass flux distributions on the boiling heat transfer process are experimentally investigated by changing the mass flux on one side of CFMC from 118 kg/m(2)center dot s to 370 kg/m(2)center dot s while keeping the mass flux on the other side unvaried. It is found that CFMC excels in heat transfer enhancement, as compared to traditional PFMC, the critical heat flux (CHF) can be increased by 42.9%-53.8%. Furthermore, the average and local heat transfer coefficient (HTC) of CFMC in the convective boiling stage can be enhanced by 33.5% similar to 62.0% and 39.3%similar to 89.4%, respectively. In the nucleate boiling stage, the average enhancement of HTC for CFMC can be up to similar to 170%. It should be noted that due to the shortening of the drying-out length and ensuring the wetting on one side, compared with the results under even mass flux distribution, the CHF can be further improved for CFMC with uneven mass flux distribution, but HTC has deteriorated. Surprisingly, all heat transfer enhancement results are achieved with a 53.4%similar to 66.7% reduction in two-phase pressure drop. Equally important, precise regulation of wall temperature distributions, heat transfer characteristics, and two-phase pressure drops can be realized by adjusting the mass fluxes on both sides. The statistical analysis of the visualization results reveals that the mass flux deployment also allows for regulating the wetting and drying times within the CFMC. This work presents essential value for optimizing the flow boiling process in microchannels and has great potential in practical applications. (c) 2022 Elsevier Ltd. All rights reserved.