Analysis of Thin-Film Evaporation Through Sintered Wick Microstructures

Abstract

Heat pipes are passive heat transport devices capable of transporting heat over long distances without a substantial drop in temperature. The topology and microstructure of the wick material play a crucial role in determining the thermal performance of such devices. Accurate modeling of pore-scale transport phenomena is thus important. In this study, pore scale analysis of thin-film evaporation through sintered copper wicks is performed. X-ray microtomography is employed to generate geometrically-faithful, feature-preserving meshes. Three commercially used sintered wicks of varying particle size ranges (45–60 μm, 106–150 μm and 250–355 μm) and with approximately 61% porosity are considered. The capillary pressure, effective pore radius, percentage thin film area and evaporative mass and heat fluxes are computed using the Volume of Fluid (VOF) model in FLUENT. Two different solution strategies are employed to stabilize the numerical solution and to improve convergence. After verifying that these strategies yield the correct solution, the VOF model is used to obtain static meniscus shapes in the pore space of the sintered wick samples. The meniscus shape is then held fixed and steady-state, thin-film evaporation analysis is performed. Liquid-vapor phase change heat transfer is modeled using a modified Schrage equation. Based on the present analysis, the best performing sample (particle size range) is identified along with the optimum contact angle.