Directional Bouncing of Impacting Droplets on Non-Uniform Rough Surfaces with High Temperature

Directional transport of high-temperature droplets enjoys broad application prospects in the fields of drag reduction and heat transfer. In this paper, two adjacent regions with different surface roughness were constructed on 304 stainless steel by laser etching to control the directional movement of high-temperature droplets. It is found that the regions with different surface roughness have different Leidenfrost temperatures, and the Leidenfrost temperature is lower under smaller roughness. When the droplet hits the boundary of the adjacent regions at high temperatures, it will bounce towards the region with larger roughness spontaneously, and the directional bouncing distance tends to first increase and then decrease with the increase of temperature and Weber number. In addition, when the droplet impacts at the boundary of the adjacent regions which have different Leidenfrost temperatures, the two parts of the droplet will be in transition boiling and film boiling respectively. The resulting Young’s force is the main factor that drives the droplets to bounce directionally.