Experimental investigation and numerical modelling of density-driven segregation in an annular shear cell

TL;DR

This study combines experimental and numerical approaches to understand density-driven segregation in granular materials within an annular shear cell, revealing how particle density differences influence segregation patterns and validating a continuum model against experimental data.

Contribution

It introduces a new continuum model for density-driven segregation and validates it with detailed experiments in an annular shear cell.

Findings

Segregation depends on density ratios and particle concentration.

The continuum model accurately predicts segregation patterns.

Experimental results show exponential shear profiles influence segregation.

Abstract

Granular materials segregate spontaneously due to differences in particle size, shape, density and flow behaviour. In this paper we experimentally investigate density-difference-driven segregation for a range of density ratios and a range of heavy particle concentrations. The experiments are conducted in an annular shear cell with rotating bumpy bottom that yields an exponential shear profile. The cell is initially filled with a layer of light particles and an upper layer of heavier grains and, on top, a load provides confinement. The segregation process is filmed through the transparent side-wall with a camera, and the evolution of particle concentration in space and time is evaluated by means of post-processing image analysis. We also propose a continuum-approach to model density-driven segregation. We use a segregation-diffusion transport equation, constitutive relations for effective viscosity and friction coefficient, and a segregation velocity analogous to the Stokes' law. The model, which is validated by comparison with experimental findings, can successfully predict density-driven segregation at different density ratios and volumetric fraction.