Silicon microchannels flow boiling enhanced via microporous decorated sidewalls

Abstract

Silicon microchannels with microporous decorated sidewalls were applied to enhance water flow boiling heat transfer, especially the critical heat flux (CHF). In experiments, a CHF of 473 W/cm2 based on the heater areas (210 W/cm2 if based on the effective heating areas) was achieved in the proposed microchannels at the mass flux of 389 kg/cm2, accounting for a 205% CHF enhancement compared with that in plain-wall microchannels without compromising the pressure drop. In addition, an improvement of 228% in effective heat transfer coefficient was achieved in the early nucleate boiling regime at the mass flux of 113 kg/cm2 compared with the plain-wall microchannels owing to the increased nucleation site density on the porous walls. Moreover, a visualization study via a microscope-linked high-speed camera was conducted to investigate the mechanism of liquid distributions and wetting phenomena in porous wall microchannels. The sustainable liquid film induced by the microporous structure greatly delays the local dryout and promotes more efficient heat transfer mechanisms such as thin-film evaporation. The exit vapor quality of the proposed microchannels has been increased above 0.3 at the tested mass flux range 113–389 kg/m2s, two times higher than that in the plain-wall microchannels (∼0.1).