Flow boiling in sintered porous copper microchannels

Abstract

Microchannel flow boiling is an effective cooling solution for high-power density electronics. Smooth wall microchannels usually suffers from boiling crisis and local dryout. In this work, we design and fabricate porous microchannel heat sink (Length × width: 20 mm × 10 mm) by sintering copper powders to significantly enhance nucleate boiling and rewetting. However, conventional sintered porous microchannels with powder base would impose large thermal resistance (low thermal conductivity of sintered copper powder, measured as 59 W m^-1 K^-1). Instead, we sintered one layer copper mesh on the bottom surface to significantly reduce the thermal resistance at solid-liquid interface. With the synergistic effect of porous wall and mesh layer, the flow boiling performances can be significantly enhanced. Three different control samples, such as conventional plain wall, sintered porous microchannel with powder base and sintered porous microchannel with mesh base, are fabricated to extensively investigate flow boiling performances. High-speed images of boiling phenomena were recorded to reveal the enhanced nucleate boiling and capillary flow. Bubble dynamics and thin-film evaporation are improved as well. Optimal thermal performance is achieved in sintered mesh porous microchannels owing to the significant decrease of thermal resistance. Compared with CNC plain-wall microchannel, the sintered porous microchannels exhibit significant enhancement in nucleate boiling performance. For example, at 70 mL min^-1, the heat transfer coefficient (HTC) is increased by about 210.3 %, while the critical heat flux (CHF) is enhanced by approximately 48.7 %. More importantly, higher heat transfer performance is achieved in the porous microchannel #2 without additional pressure drop compared to plain wall microchannel. This work provides a robust strategy for achieving highly efficient flow boiling in microchannels.