Motion of Long Levitating Drops in Tubes in an Anti-Bretherton Configuration

Phys Rev Lett. 2020 Nov 6;125(19):194501. doi: 10.1103/PhysRevLett.125.194501.

Abstract

In his seminal paper, Bretherton studied the motion of long bubbles in capillary tubes. Here, we unveil the negative configuration wherein a long liquid drop is stably transported in a capillary tube and surrounded by a flow-induced air cushion. These drops are formed when a liquid plug is pushed above a critical velocity sufficient to induce an inversion of the front meniscus with a radius of curvature smaller than the tube radius. The drop shape and lubricating air film thickness is reminiscent of Bretherton's calculation and can be inferred from an adapted analytical theory.