Propulsion Mechanisms for Leidenfrost Solids on Ratchets

TL;DR

This paper introduces a model for the propulsion of Leidenfrost solids on ratchets, based on vapor flow dynamics, providing a theoretical framework that aligns well with experimental observations.

Contribution

The paper develops a viscous drag-based model using Navier-Stokes equations and lubrication approximation to explain Leidenfrost solid propulsion on ratchets, including a scaling law for force dependence.

Findings

Model agrees with experimental data

Scaling law matches observed size dependence

Lubrication approximation effectively describes vapor flow

Abstract

We propose a model for the propulsion of Leidenfrost solids on ratchets based on viscous drag due to the flow of evaporating vapor. The model assumes pressure-driven flow described by the Navier-Stokes equations and is mainly studied in lubrication approximation. A scaling expression is derived for the dependence of the propulsive force on geometric parameters of the ratchet surface and properties of the sublimating solid. We show that the model results as well as the scaling law compare favorably with experiments and are able to reproduce the experimentally observed scaling with the size of the solid.