Flow boiling enhancement of structured microchannels with micro pin fins

Structured microchannels with micro pin fins (SM-MPF) were developed for the utilizations in advanced microchannel heat sinks to cool high heat-flux devices. These micro cone pin fins were fabricated on the bottom surface of rectangular microchannels by a laser micromilling method. Flow boiling performance of these structured microchannels with micro pin fins was experimentally explored together with comprehensive comparisons with conventional rectangular microchannels with smooth bottom walls surfaces. Flow boiling tests with two coolants, deionized water and ethanol, were performed at inlet subcoolings of 40 °C and 10 °C, mass fluxes of 200-300 kg/m2·s and effective heat fluxes up to 1067 kW/m2. Experimental results demonstrated that the structured microchannels presented significant flow boiling heat transfer enhancement, i.e., an enhancement of 10-104% in water tests, and 90-175% in ethanol cases in general, compared to the conventional rectangular microchannels. Moreover, the critical heat fluxes were promoted notably, and the severe two-phase flow instabilities were also mitigated for the structured microchannels in the low inlet temperature cases. The structured microchannels provided lots of stable nucleation sites by producing lots of tiny reentrant cavities, and introduced significant wicking effects to maintain the liquid rewetting and hinder the local dry-out, which contributed to the above notable flow boiling enhancement.