Microscale modelling of thin-film evaporation on curved wick surfaces

Thermal management of electronics is very important as the size of the electronics decreases. Two-phase cooling is one of the promising techniques at this scale as higher heat transfer rates are obtained by using the latent heat of evaporation or condensation[1]. In devices such as heat pipes and vapor chambers which employ two-phase cooling, liquid-vapor interfaces form between the wicks of these devices and the accurate prediction of heat and mass transfer from these interfaces is crucial. The design of the wicks is also important in enhancing the evaporation heat transfer. In this study, numerical investigation has been carried out to determine thin-film evaporation heat transfer from the liquid-vapor interfaces formed due to the curvature of the wick surfaces. The shapes of these interfaces are assumed to be static due to evaporation. The modelling of the evaporation phenomena from the liquid-vapor interfaces is based on kinetic theory. This microscopic modelling of evaporation has been implemented using Hertz-Knudsen-Schrage equation[2]. Two types of curved wick surfaces having convex and concave shapes are considered in this investigation. It is observed that the convex wick structures perform better than the concave ones for the parameters investigated in this study. Higher average temperatures and pressures at the interface are observed in the pores of convex wicks which is attributed to the geometry and the initial level of liquid in the pore. Evaporative mass and heat fluxes increase with the superheat of the wick surfaces and decrease with contact angle.