Enhanced flow boiling in microchannels through integrating multiple micro-nozzles and reentry microcavities

In a microchannel system, a higher mass velocity can lead to enhanced flow boiling performances, but at a cost of two-phase pressure drop. It is highly desirable to achieve a high heat transfer rate and critical heat flux (CHF) exceeding 1 kW/cm(2) without elevating the pressure drop, particularly, at a reduced mass velocity. In this study, we developed a microchannel configuration that enables more efficient utilization of the coolant through integrating multiple microscale nozzles connected to auxiliary channels as well as microscale reentry cavities on sidewalls of main microchannels. We achieved a CHF of 1016 W/cm(2) with a 50% less mass velocity, i.e., 680 kg/m(2)s, compared to the two-nozzle configuration developed in our previous studies. Two primary enhancement mechanisms are: (a) the enhanced global liquid supply by four evenly distributed micronozzles, particularly near the outlet region and (b) the effective management of local dryout by the capillary flow-induced sustainable thin liquid film resulting from an array of microscale cavities. A significantly improved heat transfer coefficient of 131 kW/m(2) K at a mass velocity of 680 kg/m(2) s is attributed to the enhanced nucleate boiling, the established capillary/thin film evaporation, and the induced advection from the present microchannel configuration. All these significant enhancements have been achieved with a similar to 55% lower two-phase pressure drop. Published by AIP Publishing.