Effect of static contact angle on the droplet dynamics during the evaporation of a water droplet on the hot walls

The effect of surface wettability on the collision dynamics and heat transfer phenomena of a single water droplet impacting upon a heated solid surface has been studied experimentally. To modify the surface wettability, two modules of stainless steel coated by TiO₂ were employed. The first module was induced by ultraviolet irradiation to produce the hydrophilic surface, while the second one was not. The diameter and the depth of coating surface were 30 mm and 200 nm, respectively. The droplet size was varied from 1.90 to 2.90 mm and substrate temperature raised up to 340 C. The interaction of an impact water droplet with a heated solid surface was investigated using a high-speed video camera. As a result, it was found that; (1) in the lower surface temperature region the evaporation time decreases as the static contact angle decreases, (2) the wetting limit temperature decreases with the increase of static contact angle, (3) the ultraviolet irradiation on the TiO₂ surface does not change the qualitative behavior of the evolution of wetting diameters, and (4) the maximum wetting diameter increases with the decrease of static contact angle below the wetting limit temperatures.