Effect of cohesive forces on fluctuations in granular flows: linking experiments and simulations

Abstract

Granular flow is a complex process depending on a large set of parameters such as grain morphology, surface friction, flow geometry, stress field and cohesion (e.g. attractive interaction between grains). The latter arises from the presence of humidity, electrostatic charges and Van der Waals forces within the grains that lead, among other effects, to the appearance of surface flow fluctuations also called avalanches. Those surface fluctuations produce an intermittent granular flow and determine the processability of a powder in many application. In order to link the flow fluctuations and the cohesion between grains, we reproduced numerically with a DEM model the flow of cohesive granular materials in a 2D rotating drum. A simplified cohesive interaction between circular grains has been implemented and the granular flow has been analyzed through the flowing angle and the interface fluctuations. The numerical results are compared with experimental results obtained with GranuDrum instrument and a set of silicon carbide grains with different grain sizes and therefore different cohesiveness. The motivation behind this study is to determine to what extent a simplified model can reproduce a complex flow. The similarities between numerical and experimental results and also the discrepancies are discussed. This comparison gives a fundamental background to the cohesive index parameter measured with GranuDrum instrument from the interface fluctuations. Finally, we show that comparing the flow inside a rotating drum obtained numerically and experimentally is a practical way to calibrate a set of parameters before the simulation of a complex process.

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