Condensed droplet growth on surfaces with various wettability

Droplet condensation, which has better heat transfer performance than film condensation, improves the efficiency of various engineering applications. Since the surface wettability decides the condensed droplet behavior, which then decides the condensation performance, the influence of the surface wettability on the droplet growth needs to be understood. In this study, four surfaces were prepared including a hydrophilic surface (surface A), two hydrophobic surfaces (surface B and C) and a superhydrophobic surface (surface D) with the droplet behavior and the droplet growth properties investigated. The results show that the droplets have non-circular triple lines and non-smooth coalescences on surface A; the droplet coalescence on surface B is smoother but still immobile; most coalescences on surface C are immobile, but the self-propelled droplet motion occurs occasionally; surface D is a superhydrophobic surface, where the self-propelled droplet motion occurs frequently. These different droplet behaviors greatly influence the droplet growth on various surfaces. Generally, with larger surface contact angle, the droplet grows more slowly, the surface coverage fraction is lower, the relative standard deviation of droplet sizes is larger. However, on the superhydrophobic surface D, the frequent self-propelled droplet motion disturbs the normal droplet growth, resulting in unpredictable droplet growth properties.