Details of soft particle clogging in two-dimensional hoppers

TL;DR

This study investigates how soft particles clog in two-dimensional hoppers, revealing that softer and less frictional particles clog more easily, with clogging influenced by gravitational force, particle stiffness, and hydrostatic pressure effects.

Contribution

It provides new insights into soft particle clogging mechanisms through combined experiments and simulations, highlighting the roles of particle softness, friction, and hydrostatic pressure.

Findings

Clogging is easier with reduced gravity or stiffer particles.

Arch size depends on hopper exit width and particle diameter for low-friction particles.

Hydrostatic pressure influences clogging in soft particles.

Abstract

We study the outflow of soft particles through quasi-two-dimensional hoppers with both experiments and simulations. The experiments utilize spheres made with soft hydrogel, silicon rubber and glass. The hopper chamber has an adjustable exit width and tilt angle (the latter to control the magnitude of gravitational forcing). Our simulation mimics the experiments using purely two-dimensional soft particles with viscous interactions but no friction. Results from both simulations and experiments demonstrate that clogging is easier for reduced gravitational force or stiffer particles. For particles with low or no friction, the average number of particles in a clogging arch depends only on the ratio between hopper exit width and particle's diameter. In contrast for the silicon rubber particles with larger frictional interactions, arches are larger than the low friction case. Additionally, an analysis of the number of particles left in the hopper when clogging occurs provides evidence for a hydrostatic pressure effect that is relevant for the clogging of soft particles, but less so for the harder (glass) or frictional (silicon rubber) particles.