Comprehensive Modeling of Capillary Flow and Evaporation in Micropillar Wicks

Porous wicks are commonly found in nature as organisms seek to leverage capillary forces for passive liquid transport. This natural mechanism has inspired great interest to incorporate wicks into engineered systems, particularly microscale devices. In this work, we modeled flow and thin film evaporation in micropillar wicks, which have been proposed for various heat transfer devices. These arrays of cylindrical pillars can generate large capillary pressures and have high permeability, enabling passive liquid supply via capillary-driven flow. The driving capillary pressure gradient entails variation of the liquid-vapor interface shape amongst micropillar cells that must be captured to accurately model physics on a millimeter scale wick. We overcame this challenge by conducting parametric studies of laminar flow and heat transfer for single micropillar cells over a range of geometries and interfacial curvatures. These parametric studies were integrated into a computationally efficient device level model that accounts for effects of local interfacial curvature on permeability and heat transfer. This modeling framework is capable of mapping pressure and temperature distributions on micropillar wicks, and can be broadly applied to porous wicks with periodic microstructures.