Flow Boiling Heat Transfer on Micro Pin Fins Entrenched in a Microchannel

Flow boiling of 1-methoxyheptafluoropropane (HFE 7000) in 222 mu m hydraulic diameter channels containing a single row of 24 inline 100 mu m pin fins was studied for mass fluxes from 350 kg/m(2) s to 827 kg/m(2) s and wall heat fluxes from 10 W/cm(2) to 110 W/cm(2). Flow visualization revealed the existence of isolated bubbles, bubbles interacting, multiple flow, and annular flow. The observed flow patterns were mapped as a function of the boiling number and the normalized axial distance. The local heat transfer coefficient during subcooled boiling was measured and found to be considerably higher than the corresponding single-phase flow. Furthermore, a thermal performance evaluation comparison with a plain microchannel revealed that the presence of pin fins considerably enhanced the heat transfer coefficient.