Deionized water flow boiling in low-surface-roughness silicon-based high aspect ratio interconnected microchannels

Deionized water is a common working fluid used for flow boiling in microchannels. However, the bubble nucleation and holding wall liquid film of deionized water in silicon-based microchannels are difficult due to the smooth channel wall with a low surface roughness. In this study, the high-aspect-ratio silicon interconnected microchannels (Ra approximate to 0.109 mu m) with slot arrays were developed with a hydraulic diameter of 114 mu m, depth of 200 mu m and width of 80 mu m. The water flow boiling characteristics were experimentally investigated at different inlet subcooling degrees, mass fluxes, and heat fluxes. The results showed individual isolated bubble was easy observed in the interconnected slot region at low inlet subcooling, which also exhibited stable nucleate boiling. While departure from nucleate boiling (DNB) was more likely to occur at high inlet subcooling and/or high heat flux. Moreover, the hydrothermal characteristics of the interconnected microchannels were also analyzed through heat transfer coefficient (HTC) and pressure drop (DP). The emergence of DNB had a strong effect on HTC whereas a slightly impact on DP. Further, the boiling heat transfer performance of the interconnected microchannels was evaluated using critical heat flux and a new evaluation parameter, the Boiling utilization. Owing to the advantages of promoting bubble nucleation, holding liquid film and stable flow patterns, the interconnected microchannels achieved a high critical heat flux. At a low mass flow rate of 0.217 g/s, the dissipated heat reached 109.8 W and 457.3 W/cm2. This study provides a new channel configuration for enhancing flow boiling in silicon-based high-aspect-ratio microchannels using water as the coolant.