Dynamics of liquid drops levitating on superheated surfaces

Abstract

The determination of the spreading dynamics and Leidenfrost temperature of drops impacting on a superheated surface is very complicated because it needs the rigorous determination of relevant time and length scales. We experimentally measured the parameters related to these phenomena for different fluid drops (water, ethanol, and FC-72). Although the drop spreading dynamics, which are represented by the maximum spreading ratio, can be qualitatively modeled by existing energy (kinetic, surface, and viscous dissipation energies) conservation theory, we find that the estimates for the surface area of the drop and the relevant length and time scales should be modified for the accuracy and generality of the model. For drops with a low Weber number, the side surface area should be considered. Further, using experimental data, we reveal that the minimum drop thickness and time scale expressed by the thickness are more suitable for describing the spreading dynamics than the drop diameter and relevant time scale. Moreover, we present a scaling procedure for the Leidenfrost temperature, for which a proper scale for the vapor film thickness is essential. As a result of the scaling analysis, the vapor film thickness scale is expressed in terms of the drop diameter and as a power function of the Weber number. Together with the scaling result, we propose a Leidenfrost temperature scale relation.