☆ 4.7 Article

Comparative study by PEPT and DEM for flow and mixing in a ploughshare mixer

POWDER TECHNOLOGY (2012)

Journal

POWDER TECHNOLOGY

Volume 228, Issue -, Pages 171-186

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ELSEVIER

DOI: 10.1016/j.powtec.2012.05.013

Keywords

Granular flow; Particle; Mixing; Ploughshare; DEM; PEPT

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Abstract

Investigation of the granular flow induced by a single plough mixer was performed using positron emission particle tracking (PEPT) and Discrete Element Modelling (DEM). Both approaches showed the development of two loops of circulation, one on either side of the plough. Particles are pushed forward through the bed by the plough and then picked up and thrown through the space above the bed, before falling to the surface and then slowly flowing back into the trench left behind the plough blade. The flow patterns obtained experimentally were compared to those obtained using DEM for a speed of 2.25 Hz and showed reasonable qualitative agreement. However, the angle of repose of the trench down which the avalanching back flow occurs was found to be too shallow in the DEM predictions. This is due to the rice grains being represented as spheres in the model - a demonstration of the modelling penalty in over-idealising particles and ignoring their shape. In contrast, the PEPT process used was unable to resolve the dilute cloud of ballistic material thrown by the plough and was also unable to identify dead regions of the bed. Uneven sampling of the phase space in PEPT can be a consequence of density and size differences between the tracer particle used and the bulk material. Mixing rates for different blade speeds were characterised for both PEPT and DEM. Good quantitative correlation was found and a consistent picture of increasing mixing efficiency with increasing plough speed was observed. Finally, observations on the averaging of PEPT and DEM data and on the comparison results from these two methods are made. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.

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PEPT validated CFD-DEM model of aspherical particle motion in a spouted bed

Hanqiao Che, Mark Al-Shemmeri, Peter J. Fryer, Estefania Lopez-Quiroga, Tzany Kokalova Wheldon, Kit Windows-Yule

Summary: Computational Fluid Dynamics coupled with Discrete Element Method (CFD-DEM) was used to model the dynamics of aspherical particles in a spouted bed. The CFD-DEM results were rigorously validated against experimental data acquired using Positron Emission Particle Tracking (PEPT). The study showed that the Young's modulus, Poisson's ratio, and restitution coefficient did not significantly affect the system's dynamics, and that Gidaspow's correlation using equivalent intrinsic particle density was suitable for modelling drag forces. The analysis demonstrated that the PEPT-validated CFD-DEM models accurately captured key features of the system, including particle circulation time, velocity and occupancy distributions, and residence time in different regions. The study also showed that models using simple, spherical particles could quantitatively reproduce the dynamics of highly aspherical materials.

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