Self-stabilization of levitating droplet clusters: A new idea and its experimental confirmation

Abstract A method of self-stabilization of a droplet cluster levitating over the locally heated water surface is proposed for the first time. The physical analysis of the problem shows that the desired result can be reached by dissolving a small amount of sodium chloride in a layer of water. This is explained by simultaneous action of two processes with opposite effects on evaporation. On the one hand, when water evaporates, a thin layer of increased salt concentration that prevents evaporation is formed at its surface. On the contrary, diffusion of salt in water decreases the surface concentration of salt. Different combinations of water heating intensity and average salt concentration are expected to result in the stable size of nearly identical levitating droplets, when there is a balance between the droplet evaporation and the condensation of vapor from the ascending vapor-air flow. The predicted phenomenon has been observed experimentally. In a series of laboratory experiments, a range of parameters has been obtained for which self-stabilization of the droplet cluster takes place. An analysis of the combined problem of heat transfer, water evaporation, and salt diffusion in water made it possible to obtain the minimum required value of the salt concentration, which is very close to that obtained experimentally.