MODELING THE COMPRESSION OF PARTICLE PACKINGS USING THE DISCRETE ELEMENT METHOD, 2008 Advanced Coating Fundamentals Symposium

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This paper concerns the use of the Discrete Element Method (DEM) for the 3D numerical simulation of the compression of particle packings in a surrounding liquid. The accuracy of DEM as a simulation tool is first assessed using X-ray Micro Tomography experiments (XMT) from the literature in the case of polydisperse particle distributions. It is shown that numerical simulations that only account for gravitational and contact forces yield loose random packings in excellent agreement with literature data. However, within the framework of paper coating processes, such gravity-driven consolidation results are not physically relevant. The reason is that the time scales of buoyancy effects are usually much larger than those related to the compression during the metering and calendering operations, and to the drag forces during the drainage of the liquid into the basesheet, which are the two main competing mechanisms governing the transient particle/pigment consolidation. In order to simulate more realistically the deposition of particles on the basesheet under drainage conditions, three modelling strategies are considered in this work, which consist of respectively taking into account: (i) gravity, (ii) mechanical compression and (iii) uniform drag compression. Drag compression is actually not uniform so that a fourth model is introduced, which explicitly takes into account the two-way coupling between the dynamics of the liquid phase and that of the solid particles. Overall results show that modelling strategies (i) and (ii) yield stratified structures and rather similar bulk porosities. On the other hand, it is observed that the use of uniform drag compression leads to significant changes in the particle dynamics and packing properties. Finally, preliminary results obtained with the two-way coupling model reveal that this novel approach shows promise for predicting compression of wet granular media.