Influence of particle size in silo discharge

Diego Gella,Diego Maza,Iker Zuriguel

doi:10.1051/epjconf/201714003021

Abstract

Recently Janda et al. [Phys. Rev. Lett. 108 , 248001 (2012)] reported an experimental study where it was measured the velocity and volume fraction fields of 1 mm diameter stainless steel beads in the exit of a two-dimensional silo. In that work, they proposed a new expression to predict the flow of granular media in silos which does not explicitly include the particle size as a parameter. Here, we study if effectively, there is not such influence of the particle size in the flux equations as well as investigate any possible effect in the velocity and volume fraction fields. To this end, we have performed high speed motion measurements of these magnitudes in a two-dimensional silo filled with 4 mm diameter beads of stainless steel, the same material than the previous works. A developed tracking program has been implemented to obtain at the same time both, the velocity and volume fraction. The final objective of this work has been to extend and generalize the theoretical framework of Janda et al. for all sizes of particles. We have found that the obtained functionalities are the same than in the 1 mm case, but the exponents and other fitting parameters are different.

Highlights

Despite it has been studied since years ago, the discharge of silos through holes is still an open problem in granular matter physics
It is well known that the flow rate of particles W is a power law of the outlet size D = 2R, so that the exponent depends on the dimensionality of the system
The ideas above are difficult to justify from a physical point of view, they have been used in diverse systems[6] and Beverloo’s expression has been proved to be useful to fit the flow rate in different circumstances[7]

Summary

Introduction

Despite it has been studied since years ago, the discharge of silos through holes is still an open problem in granular matter physics. LkTphaecfkaicntgorfra√cgtioanrisaensd ρ the from density of the the concept of pure free fall arch developed by Brown and Richards [2]. This idea assumes the existence of a parabolic [3] or hemispheric [4] region over the outlet above which the particles are subject to contact stress and under which they fall freely under the action of gravity [5]. Instead of D, Eq(1) includes a reduced outlet size D − kd involving a term proportional to the particle size This term, supported by Brown and Richards [2] and known as empty annulus, is associated with the existence of a space of indefinite size near the outlet borders where particles are forbidden to pass through. The ideas above are difficult to justify from a physical point of view, they have been used in diverse systems[6] and Beverloo’s expression has been proved to be useful to fit the flow rate in different circumstances[7]

Objectives

Methods

Results

Conclusion