Segregation by thermal diffusion in granular shear flows

TL;DR

This paper investigates how thermal diffusion causes segregation of an intruder in sheared granular gases, revealing a transition between upward and downward segregation influenced by gravity and temperature gradients.

Contribution

It extends the analysis of segregation by thermal diffusion to sheared granular gases using the inelastic Boltzmann equation, highlighting the effects of shear and gravity.

Findings

Segregation transitions depend on gravity and thermal gradients.

Shear enhances the strength and clarity of segregation mechanisms.

Phase diagrams show sensitive dependence on gravity relative to temperature gradient.

Abstract

Segregation by thermal diffusion of an intruder immersed in a sheared granular gas is analyzed from the (inelastic) Boltzmann equation. Segregation is induced by the presence of a temperature gradient orthogonal to the shear flow plane and parallel to gravity. We show that, like in analogous systems without shear, the segregation criterion yields a transition between upwards segregation and downwards segregation. The form of the phase diagrams is illustrated in detail showing that they depend sensitively on the value of gravity relative to the thermal gradient. Two specific situations are considered: i) absence of gravity, and ii) homogeneous temperature. We find that both mechanisms (upwards and downwards segregation) are stronger and more clearly separated when compared with segregation criteria in systems without shear.