Design of micropillar wicks for thin-film evaporation

The generation of concentrated heat loads in advanced microprocessors, GaN electronics, and solar cells present significant thermal management challenges in defense, space and commercial applications. Liquid to vapor phase-change strategies are promising due to the high latent heat of vaporization of the working fluid. In particular, thin-film evaporation has received increased interest owing to advances in micro/nanofabrication and the potential to dissipate high heat fluxes by increasing the evaporative meniscus area. Yet, predictive tools to design various wicking structures are limited due to the complexity of the thermal-fluidic transport. In this work, we performed systematic experiments to characterize capillary-limited thin-film evaporation from silicon micropillar wicks in the absence of nucleate boiling. The insights gained from experiments were used to model the capillary pressure, permeability, and thermal resistance. Accordingly, we developed a semi-analytical model to determine the capillary-limited dryout heat flux and wall temperature with ±20% accuracy, compared to our experiments. The model provides a versatile platform to design and optimize micropillar wicks for next generation thermal management devices.