Theoretical Leidenfrost point (LFP) model for sessile droplet

In the present paper, a theoretical investigation is undertaken in pursuit of a new mechanistically based Leidenfrost point (LFP) model for a sessile droplet. The model consists of sub-models describing temporal variations of droplet size and shape, and thickness of the vapor layer separating the droplet from the heating surface during the evaporation process. Starting from the film boiling regime, it is shown that decreasing surface temperature causes monotonic thinning of the vapor layer. The primary hypothesis of the model is that as Leidenfrost temperature is reached, the vapor layer becomes sufficiently thin to enable surface roughness protrusions to breach the droplet underside. It is shown that, because of the stochastic nature of surface roughness, an appropriate statistical parameter of surface height must be determined for comparison with the vapor layer thickness. Using surface profiles measured by the authors along with those obtained from prior studies, it is shown how this statistical parameter may be related to other commonly available parameters. Overall, the model shows good accuracy in predicting temporal records of droplet size and shape, and vapor layer thickness for different liquids and surface temperatures. Combined with the statistical surface height parameter, the model shows very good accuracy in predicting the Leidenfrost temperature, evidenced by a mean absolute error of 7.77%. (C) 2019 Elsevier Ltd. All rights reserved.