Evaporation of Leidenfrost droplet on thin soluble liquid bath with thermal non-equilibrium effect

Abstract

Leidenfrost droplet evaporation on a liquid bath exhibits unique features such as ultra-low resistance to sample transition and low-temperature operation; however, the physical mechanisms responsible for these phenomena are incompletely understood. Droplet size and temperature are two key parameters influencing Leidenfrost droplet evaporation. We report herein the thermal non-equilibrium process of an FC-72 droplet over a thin oil layer. We show that the Leidenfrost droplet radius follows the power law R(t) ∼(1 - t/τ)n, where τ is the characteristic droplet lifetime and n ranges from 0.63 to 0.91. Based on experimental results and theoretical predictions, the remarkable nonmonotonic variation of droplet temperature departs from the saturation-temperature assumption. For lower oil superheating, a cold (subcooled) droplet can sustain evaporation until it disappears. For higher oil superheating, the droplet goes through both subcooled and superheating stages. This phenomenon is well described by sensible heat absorption and release throughout droplet evaporation. These results are helpful for applications such as drug delivery, wherein a cold droplet can float on a liquid bath, thereby extending the lifetime of the biological sample in a high-temperature environment via a localized, low-temperature system.