The levitation of a droplet on a hot surface due to the rapid vaporization of the liquid at the proximity of the heat source is known as the Leidenfrost effect. This effect has been demonstrated when the surface is a solid or a liquid.
Fangye Lin, Zhejiang University, and colleagues explored the interaction between a liquid droplet and a hot granular material and found that the granual material, by essence, is a solid but adopts some behaviors similar to fluids. Their research was recently published in Physical Review Fluids.
Surprisingly, the team found that the droplet deeply penetrated the hot granular material. During the penetration process, the vapor production is so intense that the grains underneath the droplet are ejected. Consequently, the droplet moved downward under the action of gravity.
Fangye Lin sat down with the Physical Review Journal Club and discussed the team's results, which propose that granular material can be modeled as a rough surface and can be eroded when the vapor speed is sufficient.