Continuous Avalanche Segregation of Granular Mixtures in Thin Rotating Drums

TL;DR

This paper develops a continuum theory to analyze granular mixture segregation in thin rotating drums, accurately predicting experimental profiles and revealing a transition to smooth segregation as grain size differences diminish.

Contribution

It introduces a flux-dependent velocity model for surface flows, improving predictions of segregation patterns in granular mixtures.

Findings

Smallest and roughest grains localize at the drum center.

Complete segregation occurs for large size differences.

A transition to smooth segregation with power-law decay is predicted as size ratio approaches one.

Abstract

We study segregation of granular mixtures in the continuous avalanche regime (for frequencies above ~ 1 rpm) in thin rotating drums using a continuum theory for surface flows of grains. The theory predicts profiles in agreement with experiments only when we consider a flux dependent velocity of flowing grains. We find the segregation of species of different size and surface properties, with the smallest and roughest grains being found preferentially at the center of the drum. For a wide difference between the species we find a complete segregation in agreement with experiments. In addition, we predict a transition to a smooth segregation regime - with an power-law decay of the concentrations as a function of radial coordinate - as the size ratio between the grains is decreased towards one.