Dropwise Condensation Enhancement Using a Wettability Gradient

This paper deals with the modeling of dropwise condensation process on a wettability gradient surface. The proposed heat transfer model explicitly takes into account the mechanical nonequilibrium on the periphery of the droplet due to the surface-energy gradient and the contact-angle hysteresis. The model aims to predict the dynamic behavior of a droplet placed on a wettability gradient surface regarding the temperature difference between the wall and the saturated vapor. A comprehensive analysis of all the contributing thermal resistances is proposed. The influences of contact angle, temperature difference, and other representative parameters on a single droplet on a horizontal surface are also discussed. The results indicate that a wettability gradient can cause a reduction of the mean size of the droplets on the condensing surface and thus enhance significantly the heat transfer rate.