Modelling segregation of flowing bidisperse granular mixtures varying simultaneously in size and density

TL;DR

This paper develops a model for predicting segregation in flowing bidisperse granular mixtures with varying size and density, validated by DEM simulations, revealing concentration-dependent segregation directions.

Contribution

It introduces a novel segregation velocity model that accounts for combined size and density effects and their dependence on local concentration.

Findings

Segregation velocity depends linearly on shear rate and quadratically on concentration.

Predicted concentration profiles match DEM simulation results across various ratios.

Segregation direction varies with local concentration, enabling control of segregation behavior.

Abstract

Flowing granular materials segregate due to differences in particle size (driven by percolation) and density (driven by buoyancy). Modelling the segregation of mixtures of large/heavy particles and small/light particles is challenging due to the opposing effects of the two segregation mechanisms. Using discrete element method (DEM) simulations of combined size and density segregation we show that the segregation velocity is well described by a model that depends linearly on the local shear rate and quadratically on the species concentration. Concentration profiles predicted by incorporating this segregation velocity model into a continuum advection-diffusion-segregation transport model match DEM simulation results well for a wide range of particle size and density ratios. Most surprisingly, the DEM simulations and the segregation velocity model both show that the segregation direction for a range of size and density ratios depends on the local species concentration. This leads to a methodology to determine the combination of particle size ratio, density ratio, and particle concentration for which a bidisperse mixture will not segregate.