Jamming during the discharge of granular matter from a silo

TL;DR

This study investigates how granular material jams during silo discharge, revealing a power law divergence in avalanche size near a critical outlet size and showing grain shape influences jamming, but material properties do not.

Contribution

It provides experimental evidence of a power law divergence in avalanche size and highlights the influence of grain shape on jamming, with a simple interpretative model.

Findings

Avalanche size diverges near a critical outlet radius.

Material properties do not affect arch formation.

Grain shape significantly influences jamming probability.

Abstract

In this work we present an experimental study of the jamming that stops the free flow of grains from a silo discharging by gravity. When the outlet size is not much bigger than the beads, granular material jams the outlet of the container due to the formation of an arch. Statistical data from the number of grains fallen between consecutive jams are presented. The information that they provide can help to understand the jamming phenomenon. As the ratio between the size of the orifice and the size of the beads is increased, the probability that an arch blocks the outlet decreases. We show here that there is a power law divergence of the mean avalanche size for a finite critical radius. Beyond this critical radius no jamming can occur and the flow is never stopped. The dependence of the arch formation on the shape and the material of the grains has been explored. It has been found that the material properties of the grains do not affect the arch formation probability. On the contrary, the shape of the grains deeply influences it. A simple model to interpret the results is also discussed.