Take-off of small Leidenfrost droplets

TL;DR

This paper investigates the late-stage evaporation behavior of small Leidenfrost droplets, revealing a spontaneous take-off phenomenon below a critical size and establishing a theoretical relation between droplet size and elevation.

Contribution

It introduces a theoretical model linking droplet radius to elevation and demonstrates the spontaneous take-off of small droplets due to lubrication breakdown.

Findings

Droplets below a critical size spontaneously take off.

Vapor layer thickness increases as droplets become smaller.

Model predictions agree with experiments on water and ethanol droplets.

Abstract

We put in evidence the unexpected behaviour of Leidenfrost droplets at the later stage of their evaporation. We predict and observe that, below a critical size $R_l$, the droplets spontaneously take-off due to the breakdown of the lubrication regime. We establish the theoretical relation between the droplet radius and its elevation. We predict that the vapour layer thickness increases when the droplets become smaller. A satisfactory agreement is found between the model and the experimental results performed on droplets of water and of ethanol.