Dynamics of Coalesced Droplet Jumping on Superhydrophobic Surface with Asymmetrically Wettable Ridge

Abstract

Spontaneous detachment from superhydrophobic surfaces can be induced by the coalescence of two or more adjacent droplets. The phenomena have provided implications for the self-removal of droplets in the fields of self-cleaning, anti-icing, and heat transfer. However, many studies focus mainly on the theoretical jumping direction perpendicular to the substrate, although the velocity in the horizontal direction must be involved in practical applications due to various scenarios. This study analyzes numerically the effect of the distribution in ridge structure’s wettability on the performance of coalesced droplet jumping. The jumping dynamics are discussed for varying contact angle ratios and the aspect ratios of the ridge, which are the initial values for the current model. We obtain the height of the jumping and the offset distance in the horizontal direction under the several initial values. In addition, the characteristics of the asymmetric behavior are discussed based on the temporal evolution of the average velocities of the jumping droplets for each direction. Numerical results show that the horizontal offset distance is significantly pronounced at both the high asymmetry in wettability and the high aspect ratio of the ridge geometry. The phenomenon occurs when the droplet detaches from the ridge surface in the retraction process. We determine the role of the distribution within the ridge structure on its wettability, as well as the role of the aspect ratios of the ridge in facilitating the efficient transport of droplets.