Outflow and clogging of shape-anisotropic grains in hoppers with small apertures

Ashour, Ahmed; Wegner, Sandra; Trittel, Torsten; Börzsönyi, Tamás; Stannarius, Ralf

doi:10.1039/c6sm02374f

Cited by 76 publications

(79 citation statements)

References 67 publications

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“…For hard spheres, Thomas et al [12] have shown that Beverloo's equation fits the continuous flow of hard particles at high opening sizes as well as the flow within avalanches through narrow openings, and that there is no discontinuity in the dynamic parameters. This was confirmed in our earlier experiments with non-spherical hard grains [19]. For the soft spheres, the validity of Beverloo's equation cannot be tested in the limit of small orifice sizes.…”

Section: Figsupporting

confidence: 65%

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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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Section: Figsupporting

confidence: 65%

“…Even small modifications of these features can have dramatic qualitative consequences [19]. However, studies of elastic particles, for example, are rather scarce.…”

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confidence: 99%

Silo outflow of soft frictionless spheres

et al. 2017

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“…In some experiments with the hard ASB, the system produced clogs. In those cases, flow was restarted by a manually triggered airflush into the orifice [7].…”

Section: Experimental Setup and Materialsmentioning

confidence: 99%

“…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]. Despite the high practical importance of this process in agriculture, building industry, pharmacy and many other fields where grains are stored and processed, our understanding of the discharge of grains through narrow orifices is still quite incomplete.…”

Section: Introductionmentioning

confidence: 99%

High-speed x-ray tomography of silo discharge

et al. 2019

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The outflow of granular materials from storage containers with narrow outlets is studied by means of ultrafast x-ray computed tomography (UFXCT). The used acquisition speed of this tomograph is high enough to allow high-speed recording of two horizontal cross sections (each of them at a rate of 1000 images per second) of the container during the discharge of material. Analyzing space-time plots that were generated from the tomograms, we retrieve velocity profiles and packing structures in the container. We compare hard spherical grains with soft, low-friction hydrogel spheres. Their flow profiles are qualitatively different. While the hard spheres form stagnant zones at the container side walls, the hydrogel spheres with extremely low friction coefficient flow in all regions of the container. Moreover, a shell-like positional arrangement of the soft spheres induced by the container walls is revealed. The results obtained for the flow field structure confirm earlier conclusions drawn from sequences of x-ray tomograms of clogged states.

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“…The placement of an obstacle above the orifice can prevent clogging if its position is appropriately selected [6]. Other variables that have been shown to affect clogging are orifice geometry [16,17], particle shape [18][19][20], particle polydispersity [21], and gravity [22][23][24]. Nevertheless, we are not aware of any work looking at the influence of the width of the silo, a variable that in most of the existing experiments and simulations remains uncontrolled.…”

Section: Introductionmentioning

confidence: 98%

Linking bottleneck clogging with flow kinematics in granular materials: The role of silo width

et al. 2017

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We demonstrate experimentally that clogging in a silo correlates with some features of the particle velocities in the outlet proximities. This finding, that links the formation of clogs with a kinematic property of the system, is obtained by looking at the effect that the position of the lateral walls of the silo has on the flow and clogging behavior. Surprisingly, the avalanche size depends nonmonotonically on the distance of the outlet from the lateral walls. Apart from evidencing the relevance of a parameter that has been traditionally overlooked in bottleneck flow, this nonmonotonicity supposes a benchmark with which to explore the correlation of clogging probability with different variables within the system. Among these, we find that the velocity of the particles above the outlet and their fluctuations seem to be behind the nonmonotonicity in the avalanche size versus wall distance curve.

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Outflow and clogging of shape-anisotropic grains in hoppers with small apertures

Cited by 76 publications

References 67 publications

Silo outflow of soft frictionless spheres

Silo outflow of soft frictionless spheres

High-speed x-ray tomography of silo discharge

Linking bottleneck clogging with flow kinematics in granular materials: The role of silo width

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