Size Segregation of Granular Matter in Silo Discharges

TL;DR

This study investigates size-based segregation of granular materials during silo discharge, revealing surface segregation patterns and flow dynamics through experimental imaging and modeling.

Contribution

It provides new experimental insights into the surface segregation mechanism and flow behavior in silo discharges of bi-disperse granular matter.

Findings

Larger particles concentrate at the center during flow.

Segregation occurs mainly on the surface, not deep inside the flow.

Flow region is confined to a parabolic zone near the orifice.

Abstract

We present an experimental study of segregation of granular matter in a quasi-two dimensional silo emptying out of an orifice. Size separation is observed when multi-sized particles are used with the larger particles found in the center of the silo in the region of fastest flow. We use imaging to study the flow inside the silo and quantitatively measure the concentration profiles of bi-disperse beads as a function of position and time. The angle of the surface is given by the angle of repose of the particles, and the flow occurs in a few layers only near the top of this inclined surface. The flowing region becomes deeper near the center of the silo and is confined to a parabolic region centered at the orifice which is approximately described by the kinematic model. The experimental evidence suggests that the segregation occurs on the surface and not in the flow deep inside the silo where velocity gradients also are present. We report the time development of the concentrations of the bi-disperse particles as a function of size ratios, flow rate, and the ratio of initial mixture. The qualitative aspects of the observed phenomena may be explained by a void filling model of segregation.