Enhancement of flow boiling heat transfer in microchannel using micro-fin and micro-cavity surfaces

Micro-structured surfaces have a significant impact on the flow boiling process in microchannels, but few numerical studies have been carried out due to their complex nature. In this study, the numerical investi-gation of flow boiling on micro-fin, micro-cavity, and smooth surfaces in a microchannel was conducted, with water serving as the working fluid. The volume-of-fluid (VOF) method, the phase change model, and solid-fluid thermal coupling were adopted in an OpenFOAM solver to perform the computation. The en-hancing effects and detailed mechanisms of the micro-fin and micro-cavity surfaces on the heat transfer process are discussed, and the influences of wettability on these surfaces are investigated. With a contact angle of 60 degrees, the heat transfer coefficient of the micro-fin surface was 61.92% larger, and the overall ther-mal resistance was 36.64% lower than that of a smooth surface, respectively. The confined bubbles on the micro-fin surface had a much smaller dryout area on the heated wall due to the capillary wetting effect. Moreover, the micro-fin surface with the rising nucleate bubbles can induce vortexes, which strengthens the convective heat transfer. As for the micro-cavity surface, it had a moderate heat transfer enhancement with a 17.16% larger heat transfer coefficient and a 13.55% lower thermal resistance when compared with a smooth surface. When the wettability of a heating surface is enhanced, the dryout area is minimized. Thus, the heat transfer performance of the smooth and micro-cavity surfaces is enhanced. The enhance-ment resulting from modified surface wettability has less of an effect on the micro-fin surface because the micro-fin array serves a similar function to minimize the dryout area. (c) 2021 Elsevier Ltd. All rights reserved.