Stratification, segregation and mixing of granular materials in quasi-2D bounded heaps

TL;DR

This study explores how particle size ratio, flow rate, and heap rise velocity influence the formation of stratified, segregated, and mixed states in quasi-2D granular heaps, revealing new control parameters for these transitions.

Contribution

It introduces the heap rise velocity as a new control parameter affecting segregation and mixing, expanding understanding beyond previous flow rate-focused studies.

Findings

Boundary between stratified and unstratified states depends on flow rate.

Transition from segregated to mixed states depends on heap rise velocity.

Critical rise velocity varies strongly with particle size ratio.

Abstract

Segregation and mixing of granular mixtures during heap formation have important consequences in industry and agriculture. This research investigates three different final particle configurations of bi-disperse granular mixtures -- stratified, segregated and mixed -- during filling of quasi-two dimensional silos. We consider a larger number and relatively wider range of control parameters than previous studies, including particle size ratio, flow rate, system size and heap rise velocity. The boundary between stratified and unstratified states is primarily controlled by the two-dimensional flow rate, with the critical flow rate for the transition depending weakly on particle size ratio and flowing layer length. In contrast, the transition from segregated to mixed states is controlled by the rise velocity of the heap, a control parameter not previously considered. The critical rise velocity for the transition depends strongly on the particle size ratio.