Numerical investigation on settling process of bi-disperse cohesive particle clouds

Abstract

Cohesive forces lead to widespread particle flocculation, significantly altering the settling dynamics of particle clouds. The microscopic dynamics of cloud settling require further investigation, especially considering inter-particle cohesion and poly-dispersity caused by particle density variations in practical engineering applications. Motivated by this, we employ an Eulerian–Lagrangian computational fluid dynamics-discrete element method (CFD–DEM) coupling model to investigate the settling behavior of bi-disperse cohesive particle clouds in a stationary flow field. The results indicate that, for non-cohesive clouds, the large inertia of heavy particles prevents them from following the vortex back into the cloud, resulting in the upward segregation and leakage of heavy particles. The introduction of cohesion reduces the vertical particle segregation at low density ratios and intensifies segregation at high density ratios. This behavior is associated with floc formation and vortex structures. These segregation characteristics provide valuable insights into the directional recovery of heavy metal particles from wastewater. Furthermore, involving cohesion promotes the horizontal dispersion of particles by influencing the vortex structure. It contributes to a better understanding of particle dispersion in aquatic environments and providing guidance for the use of flocculants in engineering applications.