Impact of liquid droplets on heated surfaces

The phenomenon of droplet impact on heated surface happens ubiquitously in nature and in a wide range of industrial applications which include but are not limited to spray cooling and fuel-spray impingement in internal combustion engines. The impact process could be significantly affected by the heat transfer or phase change. We experimentally study the impact dynamics by high-speed imaging using liquids with different viscosities within wide ranges of Weber number and substrate temperature. We identify a mode of droplet bouncing (bouncing-with-spray mode) that can reduce the residence time significantly compared with the traditional retraction-bouncing mode. A scaling law is proposed for the transition boundary between the retraction-bouncing mode and the bouncing-with-spray mode. This study not only provides physical insight into the mechanism of the impact dynamics, but also can be helpful in the optimization of this process in the relevant applications.