Intermittent flow and transient congestions of soft spheres passing narrow orifices

Harth, Kirsten; Jing, Wang; Börzsönyi, Tamás; Stannarius, Ralf

doi:10.1039/d0sm00938e

Cited by 29 publications

(40 citation statements)

References 54 publications

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“…We perform numerical (Discrete Element Method) simulations to explore the effect of grain softness and surface friction on the flow rate as well as on the stress conditions inside the silo. Our work was motivated by recent investigations on clogging statistics of soft particles in two-dimensional hoppers [46][47][48] and X-ray tomographic measurements on the flow field of soft particles in a three-dimensional hopper [49,50], all of which noticed a fill height dependence of the clogging probability or the flow properties.…”

Section: Introductionmentioning

confidence: 99%

Flow in an hourglass: particle friction and stiffness matter

et al. 2021

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Granular flow out of a silo is studied experimentally and numerically. The time evolution of the discharge rate as well as the normal force (apparent weight) at the bottom of the container is monitored. We show, that particle stiffness has a strong effect on the qualitative features of silo discharge. For deformable grains with a Young's modulus of about Ym ≈ 40 kPa in a silo with basal pressure of the order of 4 kPa lowering the friction coefficient leads to a gradual change in the discharge curve: the flow rate becomes filling height dependent, it decreases during the discharge process. For hard grains with a Young's modulus of about Ym ≈ 500 MPa the flow rate is much less sensitive to the value of the friction coefficient. Using DEM data combined with a coarse-graining methodology allows us to compute all the relevant macroscopic fields, namely, linear momentum, density and stress tensors. The observed difference in the discharge in the low friction limit is connected to a strong difference in the pressure field: while for hard grains Janssen-screening is effective, leading to high vertical stress near the silo wall and small pressure above the orifice region, for deformable grains the pressure above the orifice is larger and gradually decreases during the discharge process. We have analyzed the momentum balance in the region of the orifice (near the location of the outlet) for the case of soft particles with low friction coefficient, and proposed a phenomenological formulation that predicts the linear decrease of the flow rate with decreasing filling height.

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Section: Introductionmentioning

confidence: 99%

Flow in an hourglass: particle friction and stiffness matter

et al. 2021

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“…It has been proposed that the clogging transition can be described with three universal variables, which can be traced to the loads and densities of granular media. Heavy tails appear in many of those systems [1,6,7] with features similar to those found in granular matter. Therefore, this study can have broad resonance in other fields.…”

Section: Introductionmentioning

confidence: 82%

On the broad tails in breaking time distributions of vibrated clogging arches

et al. 2021

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Flowing grains can clog an orifice by developing arches, an undesirable event in many cases. Several strategies have been put forward to avoid this. One of them is to vibrate the system in order to undo the clogging. Nevertheless, the time taken to break an arch under a constant vibration has a distribution displaying a heavy tail. This can lead to a situation where the average breaking time is not well defined. Moreover, it has been observed in some experiments that these tails tend to flatten for very long times, exacerbating the problem. Here we will review two conceptual frameworks that have been proposed to understand the phenomenon and discuss their physical implications.

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“…This phenomenon has been reported for pure hydrogel samples before. 25 The delay times can vary slightly between individual runs of the experiment. Compared to the pure hydrogel samples, the addition of few percents of hard grains even seems to slightly enlarge the average delay times.…”

Section: Non-permanent Cloggingmentioning

confidence: 99%

“…14 In the earlier experiments with soft, slippery hydrogel grains, it remained unexplained whether the softness of the particles (elastic modulus of the order of a few dozen kPa) or the low friction coefficient (in the order of 0.03), or a combination of both causes the quantitative differences to hard, frictional grains. Previous work on pure monodisperse hydrogel sphere (HGS) ensembles 25 has identified the viscoelastic properties of these spheres as one important feature that causes qualitatively new features of the discharge through narrow orifices.…”

Section: Introductionmentioning

confidence: 99%