Velocity and density scaling at the outlet of a silo and its role in the expression of the mass flow rate

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

doi:10.1063/1.4812021

Cited by 5 publications

(6 citation statements)

References 13 publications

(16 reference statements)

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“…Hence, distinguishing between the kinetic and contact components of the stress tensor, we accurately identify a singular region where the granular flow changes its nature and scales with the size of the orifice. Furthermore, the mean acceleration shows the same scaling, which is totally compatible with the velocity profiles obtained at the silo outlet [3,18]. As a result, the mass flow rate correlations previously introduced [1][2][3] can be consistently derived.…”

supporting

confidence: 69%

“…In both situations the coarse-graining magnitudes display monotonic behavior with height: When approaching the orifice, velocity increases and volume fraction decreases. For completeness we have checked that the kinetic profiles at z ¼ 0 are coherent with previous results [3,18].…”

supporting

confidence: 60%

“…As the gradient of contact stress is constant, regardless the outlet size, it is plausible to accept that V max is controlled by the distance from the RVE to the border of the orifice, which is in agreement with the role of R as the only characteristic length of the discharge process. Finally, based on the acceleration profiles collapsed with R, we explain the scaling of the exit velocity with ffiffiffiffiffi ffi gR p [3,18] as well as the traditional mass flow rate correlations used in engineering [ …”

mentioning

confidence: 99%

“…The ratio between normal and tangential damping coefficients was taken as ν n =ν t ¼ 3 with ν n ¼ 10 3 s −1 . Accordingly, the equations of motion were integrated with Δt ¼ 10 −6 s (more details can be found in [18,20]). A flat-bottom cylindrical container is implemented with a radius W ¼ 32r p and walls with equivalent mechanical properties to those of the particles.…”

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confidence: 99%

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Disentangling the Free-Fall Arch Paradox in Silo Discharge

et al. 2015

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Several theoretical predictions of the mass flow rate of granular media discharged from a silo are based on the spontaneous development of a free-fall arch region, the existence of which is still controversial. In this Letter, we study experimentally and numerically the particle flow through an orifice placed at the bottom of 2D and 3D silos. The implementation of a coarse-grained technique allows a thorough description of all the kinetic and micromechanical properties of the particle flow in the outlet proximities. Though the free-fall arch does not exist as traditionally understood-a region above which particles have negligible velocity and below which particles fall solely under gravity action-we discover that the kinetic pressure displays a well-defined transition in a position that scales with the outlet size. This universal scaling explains why the free-fall arch picture has served as an approximation to describe the flow rate in the discharge of silos.

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supporting

confidence: 69%

supporting

confidence: 60%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Disentangling the Free-Fall Arch Paradox in Silo Discharge

et al. 2015

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“…While there has been much progress in classifying granular behaviour experimentally [5][6][7][8][9][10][11] and using mathematical modelling [12][13][14][15], there remains a need for further work to fully understand the physics of granular phenomena. For silo flows, in particular, there is a large body of experimental and numerical work ( [16][17][18][19][20][21][22][23][24][25], for example). Most silo studies focus on the case where there is a single silo opening (where the particles discharge under gravity) located at the centre of the silo.…”

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confidence: 99%

The dynamics of granular flow from a silo with two symmetric openings

et al. 2019

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The dynamics of granular flow in a rectangular silo with two symmetrically placed exit openings is investigated using particle image velocimetry (PIV), flow rate measurements and discrete element modelling (DEM). The flow of mustard seeds in a Perspex silo is recorded using a high-speed camera and the resulting image frames are analysed using PIV to obtain velocity, velocity divergence and shear rate plots. A change in flow structure is observed as the distance L between the two openings is varied. The mass flow rate is shown to be at a maximum at zero opening separation, decreasing as L is increased; it then reaches a minimum before rising to an equilibrium rate close to two times that of an isolated (non-interacting) opening. The flow rate experiment is repeated using amaranth and screened sand and similar behaviour is observed. Although this result is in contrast with some recent DEM and physical experiments in silo systems, this effect has been reported in an analogous system: the evacuation of pedestrians from a room through two doors. Our experimental results are replicated using DEM and we show that inter-particle friction controls the flow rate behaviour and explains the discrepancies in the literature results.

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