Reemergence of Trampolining in a Leidenfrost Droplet

TL;DR

This paper investigates the spontaneous trampolining and bouncing behaviors of Leidenfrost droplets, revealing that these phenomena occur due to vapor flow instabilities and resonance effects, and are universal across different liquids and conditions.

Contribution

It demonstrates the reemergence of trampolining in Leidenfrost droplets at small sizes and proposes a resonance-based mechanism for this behavior, highlighting its universality.

Findings

Trampolining occurs at droplet sizes as low as 0.1 times the capillary length.

Resonance-driven vapor flow causes the bouncing and trampolining behaviors.

The phenomena are universal across various liquids and temperature conditions.

Abstract

The levitating Leidenfrost (LF) state of a droplet on a heated substrate is often accompanied by fascinating behaviors such as star-shaped deformations, self-propulsion, bouncing, and trampolining. These behaviors arise due to the vapor flow instabilities at the liquid-vapor interface beneath the droplet at sizes typically comparable to the capillary length scale of the liquid. Here, we report on the spontaneous bouncing, trampolining, and hovering behavior of an unconstrained LF water droplet. We observe that a droplet exhibits intermittent increase in bouncing height at specific radii and subsequent reduction in the height of bounce leading to a quiescent LF state. The reemergence of the trampolining behavior from the quiescent hovering state without any external forcing is observed at sizes as low as 0.1 times the capillary length. We attribute the droplet bouncing behavior to the dynamics of vapor flow beneath the LF droplet. We propose that the trampolining behavior of the droplet at specific radii is triggered by subharmonic and harmonic excitation of the liquid-vapor interface. We attribute the intermittent trampolining events to the change in the natural frequency of the droplet and the vapor layer due to evaporative mass loss. This proposed mechanism of resonance-driven trampolining of LF droplets is observed to be applicable for different liquids irrespective of the initial volume and substrate temperatures, thus indicating a universality of the behavior.