Experimental study on flow boiling in ultrahigh-aspect-ratio copper microchannel heat sink

One ultrahigh-aspect-ratio copper microchannel heat sink (AR = 25) was fabricated with wire electrical discharge machining technique, in which the flow boiling heat transfer of deionized water was experimentally investigated. The results show the present heat sink has a superior performance in the critical heat flux and a low thermal resistance compared to other ones (AR = 1, 5 and 15), even though its mass flux is around ten times lower than that in regular one (AR = 1). The largest improvement of critical heat flux and the maximum difference of thermal resistance are 40.95 % and 40.28 %, respectively, for the ultrahigh-aspect-ratio channel compared to those for the channel with AR = 1. It is found that the nucleate bubbles between the elongated bubbles can make full use of the remaining heat transfer area of the ultrahigh-aspect-ratio microchannel, which significantly improves its flow boiling thermal performance at a low heat flux. At a high heat flux, the nucleate bubbles generated in the deformed liquid film enhance the evaporative heat transfer process. The coexisting heat transfer mode in the ultrahigh-aspect-ratio microchannel can prolong the nucleate boiling period, which contributes to the heat transfer enhancement of the present heat sink.