Achieving ultra-uniform temperature distribution with a heterogeneous wettability surface for two-phase flow in microchannels

Abstract

Microchannel-based two-phase schemes have been proposed as an efficient solution for thermal management. However, the non-uniform temperature distribution in flow boiling limits phase-change performance and impedes commercial applications. In this study, we introduce a novel surface featuring heterogeneous wettability, comprising upstream superhydrophobic, middle plain, and downstream superhydrophilic regions. Hierarchical nanowires are employed to achieve the desired wettability, which can promote bubble departure and enhance capillary pumping. This wettability distribution facilitates upstream bubble nucleation and downstream liquid supply, significantly improving temperature uniformity. Moreover, surface contact angle variations effectively contribute to flow behavior improvement by restricting vapor reversal and fostering churn flow. Our results demonstrate that heat aggregation in the middle region and temperature restriction in the downstream region cause the high-temperature region to migrate upstream. This temperature redistribution stimulates axial heat transfer, substantially suppressing inlet subcooling and restricting temperature gradients. Compared to the plain surface, the heterogeneous wettability surface afforded an 87.8% reduction in temperature difference between Tw1 and Tw5 at approximately 120 °C, suggesting an ultra-uniform temperature distribution. Additionally, the average heat transfer coefficient showed a 35.1% enhancement rate at a wall heat flux of 100 W/cm2, and the performance evaluation criterion showed a 44.2% enhancement rate at an effective heat flux of 190 W/cm2. These results indicate that the proposed surface can efficiently regulate temperature distribution, maintain performance stability, and enhance heat transfer. The heterogeneous wettability surface has considerable potential for practical applications in high-power component heat dissipation.