Maximum size of drops levitated by an air cushion

TL;DR

This paper investigates the maximum size of liquid drops levitated by an air cushion, analyzing stability limits, experimental validation, and the development of a gas chimney that causes drop breakup.

Contribution

It introduces a boundary integral simulation approach to determine the stability and maximum size of levitated drops, revealing the existence of a critical radius and unstable solutions with gas chimneys.

Findings

Existence of a critical drop radius beyond which stable levitation is impossible.

Unstable drops develop a gas chimney leading to breakup.

Experimental data supports the theoretical and simulation results.

Abstract

Liquid drops can be kept from touching a plane solid surface by a gas stream entering from underneath, as it is observed for water drops on a heated plate, kept aloft by a stream of water vapor. We investigate the limit of small flow rates, for which the size of the gap between the drop and the substrate becomes very small. Above a critical drop radius no stationary drops can exist, below the critical radius two solutions coexist. However, only the solution with the smaller gap width is stable, the other is unstable. We compare to experimental data and use boundary integral simulations to show that unstable drops develop a gas "chimney" which breaks the drop in its middle.