Localization-delocalization transitions in turbophoresis of inertial particles

TL;DR

This paper challenges the traditional view of turbophoresis by showing that inertial particles can escape minima, leading to a phase transition that causes light particles to concentrate while heavy particles disperse, with broad implications.

Contribution

It provides an analytical solution revealing a phase transition in turbophoresis, showing particles can escape minima, which alters the fundamental understanding of the phenomenon.

Findings

Particles can escape minima if their equilibration time exceeds the time to reach the minimum.

A phase transition occurs as a sign change of the mean velocity.

Light particles concentrate in minima, heavy particles disperse away from minima.

Abstract

Small aerosols drift down temperature or turbulence gradient since faster particles fly longer distances before equilibration. That fundamental phenomenon, called thermophoresis or turbophoresis, is widely encountered in nature and used in industry. It is universally believed that particles moving down the kinetic energy gradient must concentrate in minima (say, on walls in turbulence). Here we show that this is incorrect: escaping minima is possible for inertial particles whose time of equilibration is longer than the time to reach the minimum. The best way out is always through: particles escape by flying through minima or reflecting from walls. We solve the problem analytically and find the phase transition as a sign change of the mean velocity. That means separation: light particles concentrate in a minimum while heavy particles spread away from it (gravity can reverse the effect). That discovery changes understanding of that fundamental phenomenon and may find numerous applications.