Discharge of liquid and grains from a silo with multiple orifices

Abstract

Using a multi-orifice cylindrical silo, the average flow rates Q1 and QN through one and N orifices, respectively, were first measured for the discharge of water or dry grains and then for the mixture. As expected, QN=NQ1 for monophasic discharges. Nevertheless, for the mixture, QN≪NQ1, and the effect becomes more notorious as N augments and when the grain size is decreased. A simplified continuum model of a flow through a dynamic porous medium, with hydrodynamic resistance that increases with N, is used to reproduce the experimental results. Additional analysis in a two-dimensional cell reveals interacting parabolic flow profiles of the immersed particles close to the orifices, with a reduction in the average velocities when N is increased, which helps to understand the non-additivity of the total flow rate.