Modeling Stratified Segregation in Periodically Driven Granular Heap Flow

TL;DR

This paper develops a continuum model for stratified segregation in periodically driven granular heap flows, showing how feed rate modulation can produce well-segregated layers and reduce concentration variation during discharge.

Contribution

It introduces a novel advection-diffusion-segregation model for unsteady granular flows with periodic feed rate modulation, capturing transient segregation dynamics.

Findings

Periodic feed rate modulation creates well-segregated layers.

Layered segregation reduces streamwise segregation at high particle-size ratios.

Modulation significantly decreases concentration variation during hopper discharge.

Abstract

We present a continuum approach to model segregation of size-bidisperse granular materials in unsteady bounded heap flow as a prototype for modeling segregation in other time varying flows. In experiments, a periodically modulated feed rate produces stratified segregation like that which occurs due to intermittent avalanching, except with greater layer-uniformity and higher average feed rates. Using an advection-diffusion-segregation equation and characterizing transient changes in deposition and erosion after a feed rate change, we model stratification for varying feed rates and periods. Feed rate modulation in heap flows can create well-segregated layers, which effectively mix the deposited material normal to the free surface at lengths greater than the combined layer-thickness. This mitigates the strong streamwise segregation that would otherwise occur at larger particle-size ratios and equivalent steady feed rates and can significantly reduce concentration variation during hopper discharge. Coupling segregation, deposition and erosion is challenging but has many potential applications.