Pool boiling heat transfer enhancement by porous interconnected microchannel nets at different liquid subcooling

Abstract

Porous interconnected microchannel nets are fabricated in this study using copper powder sintering and wire electric discharge machining. Pool boiling experiments are conducted with this enhanced structure using deionized water as a working fluid at atmospheric pressure with variation in the liquid subcooling. The results of this study indicate that the enhanced structure yields a higher heat transfer coefficient (HTC) than its solid copper counterpart at any liquid subcooling and suppresses the temperature excursion by lowering the wall superheat at the onset of nucleate boiling (ONB). Lowering the liquid subcooling temperature increases the HTC, which is more prevalent at the low heat fluxes. High-speed visualization at 2000 frames/s demonstrates that the bubble departure diameter of the enhanced structure is smaller than that of the solid structure and increases with increasing heat flux for qa ≤ 475 kW/m2 but decreases for qa > 475 kW/m2. Bubble growth at low heat fluxes (qa ≤ 475 kW/m2) is governed by both the inertia-driven and the heat-transfer-driven regimes; whereas, it is governed only by inertia-driven effects for qa > 475 kW/m2. Increasing the liquid subcooling temperature reduces the bubble departure diameter but has little influence on bubble growth.