Disentangling the Free-Fall Arch Paradox in Silo Discharge

Rubio-Largo, S.M.; Janda, Álvaro; Maza, Diego; Zuriguel, Iker; Hidalgo, R. C.

doi:10.1103/physrevlett.114.238002

Cited by 126 publications

(115 citation statements)

References 22 publications

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“…Moreover, they have found that, instead of considering a reduce outlet, a dilatancy at the outlet should be taken into account (φ 0 ≈ φ b [1−α 1 e −α 2 D ]). A recent work [10] has shown that close to the outlet, the particles are accelerated leading to the scaling of the velocity, but not in an idealised free fall. We adapted this model to propose a new expression for the flow rate :…”

Section: Resultsmentioning

confidence: 99%

Discharge flow of a granular media from a silo: effect of the packing fraction and of the hopper angle

2017

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Abstract. Silos are widely used in the industry. While empirical predictions of the flow rate, based on scaling laws, have existed for more than a century (Hagen 1852, translated in [1] -Beverloo et al. [2]), recent advances have be made on the understanding of the control parameters of the flow. In particular, using continuous modeling together with a mu(I) granular rheology seem to be successful in predicting the flow rate for large numbers of beads at the aperture (Staron et al.[3], [4]). Moreover Janda et al. [5] have shown that the packing fraction at the outlet plays an important role when the number of beads at the apeture decreases. Based on these considerations, we have studied experimentally the discharge flow of a granular media from a rectangular silo. We have varied two main parameters: the angle of the hopper, and the bulk packing fraction of the granular material by using bidisperse mixtures. We propose a simple physical model to describe the effect of these parameters, considering a continuous granular media with a dilatancy law at the outlet. This model predicts well the dependance of the flow rate on the hopper angle as well as the dependance of the flow rate on the fine mass fraction of a bidisperse mixture.

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Section: Resultsmentioning

confidence: 99%

Discharge flow of a granular media from a silo: effect of the packing fraction and of the hopper angle

2017

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“…D is reduced by kd avg due to boundary effects, where d avg characterizes the grain size, and k is an order-one constant [2]. Recent studies [17,18] have provided micromechanical insights into this equation with a coarse-grain technique. An important open question concerns the relevance of this relation for non-spherical particles.…”

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confidence: 99%

Orientation, flow, and clogging in a two-dimensional hopper: Ellipses vs. disks

Tang

Behringer

2016

EPL

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-Two-dimensional (2D) hopper flow of disks has been extensively studied. Here, we investigate hopper flow of ellipses with aspect ratio α = 2, and we contrast that behavior to the flow of disks. We use a quasi-2D hopper containing photoelastic particles to obtain stress/force information. We simultaneously measure the particle motion and stress. We determine several properties, including discharge rates, jamming probabilities, and the number of particles in clogging arches. For both particle types, the size of the opening, D, relative to the size of particles, is an important dimensionless measure. The orientation of the ellipses plays an important role in flow rheology and clogging. The alignment of contacting ellipses enhances the probability of forming stable arches. This study offers insight for applications involving the flow of granular materials consisting of ellipsoidal shapes, and possibly other non-spherical shapes.Hopper flows of granular materials involve dynamical granular states with important industrial applications [1,2]. Time-averaged granular flow theories, often using hopper flow as a test case, have progressed from continuum mechanics models to mesoscopic models [2][3][4][5][6]. Fluctuations and clogging (or jamming) are also important characteristics for hopper flow. Experiments [7][8][9] have examined the the clogging transition of hopper flow for different grain properties and hopper geometries. Most recent results from [8] imply that all hoppers have a nonzero probability to clog. Other studies [10][11][12][13][14][15] have also sought to understand flow and clogging (or jamming) mechanisms from a microscopic viewpoint. However, for simplicity, theories developed from the above studies often tend to assume spherical particles, including disks in two dimensions (2D). The effect of particle shape on hopper flow is usually not their focus. In reality, particle shapes are often not spherical; rice and M&M's are roughly ellipsoids; sand particles have irregular shapes. Thus, it is scientifically and industrially relevant to explore how particle shape affects flow rheology and clogging mechanisms.A simple way to explore particle shape effects is to contrast 2D hopper flows of disks and ellipses for the time-averaged discharge rate,Ṁ , and jamming probability. Discharge rates of hopper flow often follow the wellestablished Beverloo equation [16], which relatesṀ to the hopper opening size, D :Ṁ ∝ (D − kd avg ) (n−1/2) , where n is the spatial dimension (e.g. n = 2 or 3 for two or three-dimensional systems). D is reduced by kd avg due to boundary effects, where d avg characterizes the grain size, and k is an order-one constant [2]. Recent studies [17,18] have provided micromechanical insights into this equation with a coarse-grain technique. An important open question concerns the relevance of this relation for non-spherical particles. Several studies have used DEM simulation methods to understand how the aspect ratio of an ellipse could affect the discharge rate [21][22][23][24][25][26][...

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“…When the outlet diameter is smaller than about 5 particle diameters [9][10][11][12][13], clogs form after some time at the orifice and block further outflow, mostly unwanted. Spontaneous arch formation [14,15], the preceding kinetics [16], as well as the inherent force distributions [17,18] have been analyzed in the literature. In order to study the geometry and statics of such clogs, often 2D container geometries are chosen.…”

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confidence: 99%

Silo outflow of soft frictionless spheres

et al. 2017

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Outflow of granular materials from silos is a remarkably complex physical phenomenon that has been extensively studied with simple objects like monodisperse hard disks in two dimensions (2D) and hard spheres in 2D and 3D. For those materials, empirical equations were found that describe the discharge characteristics. Softness adds qualitatively new features to the dynamics and to the character of the flow. We report a study of the outflow of soft, practically frictionless hydrogel spheres from a quasi-2D bin. Prominent features are intermittent clogs, peculiar flow fields in the container and a pronounced dependence of the flow rate and clogging statistics on the container fill height. The latter is a consequence of the ineffectiveness of Janssen's law: the pressure at the bottom of a bin containing hydrogel spheres grows linearly with the fill height.

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Disentangling the Free-Fall Arch Paradox in Silo Discharge

Cited by 126 publications

References 22 publications

Discharge flow of a granular media from a silo: effect of the packing fraction and of the hopper angle

Discharge flow of a granular media from a silo: effect of the packing fraction and of the hopper angle

Orientation, flow, and clogging in a two-dimensional hopper: Ellipses vs. disks

Silo outflow of soft frictionless spheres

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