Thermal Performance Modeling of Liquid in Evaporator with Spherical Microstructures and Conical Micropillars

The heat transfer performance of passive two-phase cooling devices such as heat pipes and vapor chambers is mainly depend on the topology and geometry of wick and evaporator microstructures. The desired characteristics of evaporator microstructures are high permeability, high wicking capability and large extended meniscus area that sustains thin-film evaporation which choices of scale and porosity lead to trade-offs between the desired characteristics. In the present study, the free-surface shapes of the static liquid meniscus in spherical microstructures and conical micropillar were modeled using gradient decent algorithm of Surface Evolver software and the non-dimensional capillary pressure was determined based on curvature of surface. Permeability and heat transfer coefficient were computed using Fluent software as functions of the nondimensional geometrical parameter and the contact angle between the liquid and solid. Based on these performance parameters, due to high heat contact surface, decrease of cross section, increase of permeability and increase of thin film liquid due to extention of liquid on inclined surface, conical microstructures provide more efficient and desirable geometry for wicking and thin-film evaporation. The solid-liquid contact angle and geometrical parameter that yield the best performance were also identified.