Coarse-grained DEM study of solids sedimentation in water

The so-called coarse-grained discrete element method (DEM) is used here for efficient simulations of large-scale particle systems as its effectiveness has been successfully verified previously on the processes such as spouted beds, pneumatic conveying systems and bubbling fluidized beds. In this study, the coarse-grained DEM method is used to study the solid-liquid flow in the process of sedimentation of solids in water. Four specific types of particle systems are considered to verify the effectiveness of the coarse-grained model qualitatively and quantitatively, the particle systems considered being: the original-sized particle system; the coarse-grained particle systems in two different coarse graining ratios, and the simple large particle system. For qualitative evaluations of these systems, the evolutions of the sedimentation state, characterized by fluid velocity distributions and contour maps of void fractions, are compared using a range of snapshots at different times. For quantitative comparisons, the physical indexes such as the change of particle volume fraction, the potential energy of particles and liquid pressure changes are evaluated. These systems are also compared using four cases with different variable values for further investigation of the effectiveness of the coarse graining DEM method under different conditions. The four cases consist of one base case and three parametric cases which are different in terms of the particle number and height of the computational domain. These comparisons show that, for all four cases, the coarse-grained system in fact produces results that are in good agreement with those of the original-sized particle system both qualitatively and quantitatively. However, the simple large particle system fails to achieve a reasonable agreement with the original-sized particle system. It can be thus concluded that the coarse-grained model is a cost-effective and reliable tool to simulate the process of large-scale solids sedimentation in water. (C) 2019 Elsevier B.V. All rights reserved.