Enhanced flow boiling heat transfer in manifold pin-fin microchannel heat sink

Flow boiling heat transfer in manifold microchannels (MMCs) is generally hindered by non-uniform wall rewetting, which limits their application in thermal management of electronic devices. In this work, parallel and staggered pin-fin microchannel (PPFM and SPFM) are integrated into MMC. The flow boiling heat transfer and hydraulic performance of PPFM and SMPF is compared with that of straight microchannel (SM) sharing identical geometric parameters. When the heat flux is sufficiently high, periodic vapor backflow is observed in all three heat sinks, which impedes wall rewetting and is a directly cause of heat transfer deterioration. PPFM and SPFM suppress vapor backflow and improve the uniformity of wall rewetting by creating transverse flow between fins, which prevent sustained wall dry-out. Compared to SM, improvements in HTC of up to 45.6% and 34.8% are achieved in PPFM and SPFM, respectively, along with improvements in average HTC of up to 15.6% and 22.5%. By providing a larger flow passage, PPFM and SPFM achieve reductions in the average two-phase pressure drop of up to 45.5% and 42.1%, respectively. Consequently, the average COP is enhanced by up to 93.3% and 71.7% in PPFM and SPFM, respectively. When the periodic vapor backflow is triggered, the formation and breakdown of annular flow in inlet manifold induce significant pressure drop fluctuations. The pin-fin microchannels mitigate this instability by balancing pressure among channels and suppressing vapor backflow, achieving maximum reductions in the standard deviation of pressure drop fluctuations of 21.3% for PPFM and 44.2% for SPFM.