Self-Propulsion of Boiling Droplets on Thin Heated Oil Films

TL;DR

This paper investigates how boiling droplets can self-propel on thin heated oil films, driven by microsecond fluctuations and asymmetric vapor release, achieving velocities comparable to Leidenfrost droplets.

Contribution

It introduces a new understanding of droplet propulsion mechanism involving coupling of short and long timescale phenomena at the droplet-oil interface.

Findings

Droplets attain high velocities similar to Leidenfrost droplets.

Microsecond fluctuations at the interface drive asymmetric vapor release.

A coupled model explains the propulsion mechanism.

Abstract

We report on the self-propulsion of boiling droplets which, despite their contact with viscous, immiscible oil films, attain high velocities comparable to those of levitating Leidenfrost droplets. Experiments and model reveal that droplet propulsion originates from a coupling between seemingly disparate short and long timescale phenomena due to microsecond fluctuations induced by boiling events at the droplet-oil interface. This interplay of phenomena leads to continuous asymmetric vapor release and momentum transfer for high droplet velocities.