Droplets jump at the cluster coalescence with the locally heated liquid layer

The effect of a droplet ejection upward during the collapse of a droplet cluster is described for the first time. Using a high-speed camera, the dynamics of the droplet motion is studied, based on which the average velocity of the steam– air flow along the droplet trajectory above the locally heated water surface is estimated. It was found that, for the largest observed droplets, the aerodynamic drag force by the Stokes’ law at this average velocity does not exceed their weight. This confirms the fast decay of the flow velocity with the height over the layer. We hypothesize that the thin gas interlayer between the droplet and the evaporating water surface affects the droplet clusters levitation mechanism and ensures the resistance of such droplets to coalescing with the subjacent water layer.