Clogging of soft particles in two-dimensional hoppers

Abstract

Using experiments and simulations, we study the flow of soft particles through quasi-twodimensional hoppers. The first experiment uses oil-in-water emulsion droplets in a thin sample chamber. Due to surfactants coating the droplets, they easily slide past each other, approximating soft frictionless disks. For these droplets, clogging at the hopper exit requires a narrow hopper opening only slightly larger than the droplet diameter. The second experiments use soft hydrogel particles in a thin sample chamber, where we vary gravity by changing the tilt angle of the chamber. For reduced gravity, clogging becomes easier, and can occur for larger hopper openings. Our simulations mimic the emulsion experiments and demonstrate that softness is a key factor controlling clogging: with stiffer particles or a weaker gravitational force, clogging is easier. The fractional amount a single particle is deformed under its own weight is a useful parameter measuring particle softness. Data from the simulation and hydrogel experiments collapse when compared using this parameter. Our results suggest that prior studies using hard particles were in a limit where the role of softness is negligible which causes clogging to occur with significantly larger openings.

High-speed x-ray tomography of silo discharge

“…For a large variety of hard, frictional spherical grains, it has been shown that the diameter of the opening must be larger than approximately five times the particle diameter to avoid clogs [1,2]. When the particles are soft and slippery, they flow through much narrower outlets without clogging [3][4][5]. For non-spherical particles, shape parameters influence the discharge statistics [6,7].…”

“…with the determination of flow rates [1,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], the statistics of clogging [2,[23][24][25][26][27][28][29][30], the influences of obstacles near the orifice on the flow rates [31,32], and the role of gravity and embedding fluids [33][34][35]. The role of softness has been considered only recently in a few papers [3][4][5].…”

Redefining the role of obstacles in pedestrian evacuation

“…Pedestrian systems are probably the most dramatic example of clogging, but this phenomenon is rather general for systems composed of many discrete particles that flow through constrictions. Indeed, this topic has been the focus of research in a variety of fields such as microbial populations [8], colloids [9], droplets [10], granular matter [11] or robots [12]. Recently a phase diagram has been proposed to encompass clogging in such many different systems [13].…”

Disordered contact networks in jammed packings of frictionless disks

“…Soft particle packings, which yield hard particle systems in the limit of zero overlap, have also been the subject of considerable interest [32,33,34,35]. Recently such packings of soft frictionless particles have also been realized experimentally [36,37,38,39].…”