Lattice Boltzmann modeling of self-propelled Leidenfrost droplets on ratchet surfaces

TL;DR

This study uses a thermal multiphase lattice Boltzmann model to simulate and analyze the self-propelled motion of Leidenfrost droplets on ratchet surfaces, revealing the effects of surface asymmetry, aspect ratio, and inclination on droplet dynamics.

Contribution

It introduces a validated lattice Boltzmann model for simulating evaporation and droplet motion on ratchet surfaces, providing new insights into the mechanisms of self-propulsion and uphill climbing.

Findings

Droplets move toward the slowly inclined side of ratchets, consistent with experiments.

A critical ratchet aspect ratio maximizes droplet velocity.

Maximum inclination angle for uphill climbing depends on initial droplet radius.

Abstract

In this paper, the self-propelled motion of Leidenfrost droplets on ratchet surfaces is numerically investigated with a thermal multiphase lattice Boltzmann model with liquid-vapor phase change. The capability of the model for simulating evaporation is validated via the D2 law. Using the model, we first study the performances of Leidenfrost droplets on horizontal ratchet surfaces. It is numerically shown that the motion of self-propelled Leidenfrost droplets on ratchet surfaces is owing to the asymmetry of the ratchets and the vapor flows beneath the droplets. It is found that the Leidenfrost droplets move in the direction toward the slowly inclined side from the ratchet peaks, which agrees with the direction of droplet motion in experiments [Linke et al., Phys. Rev. Lett., 2006, 96, 154502]. Moreover, the influences of the ratchet aspect ratio are investigated. For the considered ratchet surfaces, a critical value of the ratchet aspect ratio is approximately found, which corresponds to the maximum droplet moving velocity. Furthermore, the processes that the Leidenfrost droplets climb uphill on inclined ratchet surfaces are also studied. Numerical results show that the maximum inclination angle at which a Leidenfrost droplet can still climb uphill successfully is affected by the initial radius of the droplet.