Flow boiling performance in pin fin- interconnected reentrant microchannels heat sink in different operational conditions

Abstract

Pin fin-interconnected reentrant microchannels (PFIRM) are proposed and developed for microchannel heat sinks cooling systems to combine both merits of reentrant cavities and micro pin fins in heat transfer enhancement. They feature two directions of reentrant microchannels with a intersection angle of 30° in the downside, and staggered arrays of micro diamond pin fins on the upper side. Micro-milling process is utilized to process the interconnected reentrant microchannels, which simultaneously induces the formation of micro diamond pin fins. Flow boiling experiments are conducted using two coolants (deionized water and ethanol) at inlet subcoolings of 40 °C and 10 °C, mass fluxes of 125–300 kg/(m2 s). Flow boiling heat transfer, pressure drop and two-phase flow instabilities of the PFIRM are systematically assessed. It is found that the PFIRM showed a 39–284% enhancement in two-phase heat transfer in water tests, and a 29–220% in ethanol tests compared to the parallel reentrant microchannels. Decrease of bubble confinement effect by the interconnected microchannels and ideal spaces for the bubble nucleation and movement supplied by the reentrant chambers contributed to the above boiling heat transfer enhancement of PFIRM. The PFIRM heat sink operated more efficiently using the coolant of water than ethanol.