Intermittent flow and transient congestions of soft spheres passing narrow orifices

TL;DR

This study investigates how soft hydrogel spheres discharge from silos, revealing that their flow becomes intermittent and can spontaneously resolve, contrasting with rigid particles due to viscoelastic effects.

Contribution

It provides new insights into the flow dynamics of soft particles, highlighting the fill-height dependence and spontaneous clog dissolution caused by viscoelasticity.

Findings

Flow becomes more fluctuating with smaller orifice and lower fill height

Flow can stop and spontaneously restart in narrow orifices

Viscoelasticity causes slow reorganization leading to non-permanent congestions

Abstract

Soft, low-friction particles in silos show peculiar features during their discharge. The outflow velocity and the clogging probability both depend upon the momentary silo fill height, in sharp contrast to silos filled with hard particles. The reason is the fill-height dependence of the pressure at the orifice. We study the statistics of silo discharge of soft hydrogel spheres. The outflow is found to become increasingly fluctuating and even intermittent with decreasing orifice size, and with decreasing fill height. In orifices narrower than two particle diameters, outflow can stop completely, but in contrast to clogs formed by rigid particles, these congestions may dissolve spontaneously. We analyze such non-permanent congestions and attribute them to slow reorganization processes in the container, caused by viscoelasticity of the material.