Flow Boiling Heat Transfer in Microchannel Cold Plate Evaporators for Electronics Cooling

The local two-phase heat transfer coefficient is a critical parameter in the design of microchannel cold plate evaporators used in applications such as electronics cooling systems. Only a few past studies on microchannels have investigated the heat transfer characteristics over the entire vapor quality range and conflicting trends have been reported even in these studies. Therefore, the present study focuses on the investigation of the local flow boiling heat transfer coefficient at different vapor qualities of the refrigerant R-134a. An experimental setup was built to measure the local heat transfer coefficient and to obtain a better understanding of the underlying physics. Two evaporators were considered in this study. They employ parallel microchannels with 1.09 and 0.54 mm hydraulic diameter and an aspect ratio of 2.5. Measurements were conducted at saturation temperatures ranging from 9 to 29°C, mass fluxes from 20 to 300 kg m s and wall heat fluxes of up to 20 W cm. A comparison between measurements and established correlations from the literature is presented.