Effect of an electric field on an intermittent granular flow

Granular gravity driven flows of glass beads have been observed in a silo with a flat bottom. A DC high electric field has been applied perpendicularly to the silo to tune the cohesion. The outlet mass flow has been measured. An image subtraction technique has been applied to visualize the flow geometry and a spatiotemporal analysis of the flow dynamics has been performed. The outlet mass flow is independent of voltage, but a transition from funnel flow to rathole flow is observed. This transition is of probabilistic nature and an intermediate situation exists between the funnel and the rathole situations. At a given voltage, two kinds of flow dynamics can occur : a continuous flow or an intermittent flow. The electric field increases the probability to observe an intermittent flow.Comment: Accepted for publication in PRE on Apr 9, 201

Analysis of pressure evolution in granular materials in converging bins during filling and emptying processes

A simplified analysis of deformation and stress states in converging hoppers during filling and discharge of granular material is presented. In particular we discuss a method for solving the set of differential equations governing the flow of granular material in a plane wedge hopper. The equilibrium conditions and stress-strain relations are satisfied for the planar slice elements assuming the dependence of displacement and stress on the Cartesian coordinate z. The transient flow of an icompressible, cohesionless granular material in a two-dimensional converging hopper is considered. We assume the material to be in elastic or elasto-plastic states within the hopper satisfying the Coulomb yield condition and the non-associated flow rule. The paper presents a detailed analysis of the evolution of pressure acting on the hopper wall during the filling and emptying processes when the initial active state of pressure is transformed into a passive state. Analytical and numerical analyses are presented. It is shown that at the initial stage of the emptying process a considerable switch overpressure develops, exceeding the steady-state passive pressure several times

Optical technique DPIV in measurements of granular material flows, Part 1 of 3 -- plane hoppers

The aim of this paper is topresen the evolution of plug flow developin in threedeneqR packedgranTRT materialsin the model of a hopper made of Plexiglas. For this purpose, the digital particle image velocimetry (DPIV)technqR4 is applied toandyRM the flow field of thegranMTy material.When discharge starts, a plug flowzon in the flowin material expanK upward. This zonchandM its width reachin the upper surface of the material. The plug flow evolution as afun;ddq of time is describedusin DPIV. Thistechn;Rd yields the velocity profiles of flowin gran4R; materials, velocitymagntyqK contyqK vector fields, velocity distribution on certain levelsin the modelan traces of the selected particles. The results obtainq for the evolution of the vertical velocity, heightan width of the plug flow zon as a fun;KqB of time, measured at the symmetry axis of the model for theamaran;M seed are compared to the results obtainq by Watersan Drescher.Measuremen; of thestagnJJ bounJJ as afunyMTq of time are compared to the results availablein the literature