Diffusion, mixing, and segregation in confined granular flows

TL;DR

This study uses simulations and continuum modeling to explore how pressure influences diffusion and segregation in confined granular flows, revealing conditions that promote mixing or segregation.

Contribution

It introduces a pressure-dependent continuum model that accurately predicts segregation and diffusion behaviors in bidisperse granular flows.

Findings

Diffusion is independent of overburden pressure.

Segregation rate decreases with increasing pressure.

High pressure can suppress segregation, promoting mixing.

Abstract

Discrete element method simulations of confined bidisperse granular shear flows elucidate the balance between diffusion and segregation that can lead to either mixed or segregated states, depending on confining pressure. Results indicate that the collisional diffusion is essentially independent of overburden pressure. Because the rate of segregation diminishes with overburden pressure, the tendency for particles to segregate weakens relative to the re-mixing of particles due to collisional diffusion as the overburden pressure increases. Using a continuum approach that includes a pressure dependent segregation velocity and a pressure independent diffusion coefficient, the interplay between diffusion and segregation is accurately predicted for both size and density bidisperse mixtures over a wide range of flow conditions when compared to simulation results. Additional simulations with initially segregated conditions demonstrate that applying a high enough overburden pressure can suppress segregation to the point that collisional diffusion mixes the segregated particles.