Numerical analysis of flow and heat transfer characteristics in porous wick of heat pipe

This paper studies the effects of wick structure on thermal performance of heat pipe. The liquid meniscus models are established for various wick structures using Surface Evolver software, and the meniscus models are validated by experimental data. The capillary force and velocity of capillary rise are calculated for sphere, column, and cuboid structures. The results indicate that the absolute values of capillary force decrease with increasing of contact angle and porosity. The sphere structure exhibits the highest absolute capillary force. Increasing the porosity and the diameter of wick enhances the permeability of the porous structure, which reduces flow resistance and consequently increases velocity of capillary rise. The evaporation model imposed by using user-defined function (UDF) is further employed to study the evaporative heat transfer characteristics of wick structure. The calculation results are validated by available experimental data for the rectangular microchannel. The effects of solid-liquid contact angle, porosity, liquid level, superheat and Marangoni convection on the evaporation heat transfer at the vapor-liquid interface are investigated. It is found that the fluxes of mass andheat at the interface decrease with increases of contact angle, liquid level, and porosity. The evaporative mass flux increases linearly with superheat. When the superheat exceeds 5 K, Marangoni convection significantly enhances the evaporation process. Comparative study demonstrates that the sphere structure achieves superior evaporation efficiency compared to column and cuboid structures. Such conclusion is referential for the selection and design of the basic structures for the porous wick of heat pipe.