Silo discharge of mixtures of soft and rigid grains

TL;DR

This study investigates how mixtures of soft elastic and hard frictional grains influence silo discharge and clogging, revealing that even small amounts of hard grains significantly affect flow dynamics and arch formation.

Contribution

It provides the first detailed comparison of clogging behavior and flow dynamics in mixtures of soft and hard grains, highlighting the role of inter-species friction.

Findings

Small amounts of hard grains alter clogging probabilities.

Mixtures affect arch formation and flow velocities.

Experimental results align with numerical simulations.

Abstract

We study the outflow dynamics and clogging phenomena of mixtures of soft, elastic low-friction spherical grains and hard frictional spheres of similar size in a quasi-two-dimensional (2D) silo with narrow orifice at the bottom. Previous work has demonstrated the crucial influence of elasticity and friction on silo discharge. We show that the addition of small amounts, even as low as 5\%, of hard grains to an ensemble of soft, low-friction grains already has significant consequences. The mixtures allow a direct comparison of the probabilities of the different types of particles to clog the orifice. We analyze these probabilities for the hard, frictional and the soft, slippery grains on the basis of their participation in the blocking arches, and compare outflow velocities and durations of non-permanent clogs for different compositions of the mixtures. Experimental results are compared with numerical simulations. The latter strongly suggest a significant influence of the inter-species particle friction.