Study of sedimentation of non-cohesive particles via CFD-DEM simulations

TL;DR

This study uses CFD-DEM simulations to analyze non-cohesive particle sedimentation, validating models, exploring segregation, and linking contact forces to effective stress in soil mechanics, providing insights into sedimentation dynamics and deposition stages.

Contribution

The paper introduces a validated CFD-DEM model for sedimentation, demonstrating segregation effects, and connecting contact forces to effective stress principles in soil mechanics.

Findings

Segregation decreases with higher initial solid concentration.

Effective stress principle is demonstrated via contact forces.

Deposition stage and critical sedimentation time are characterized.

Abstract

The sedimentation process of granular materials exists ubiquitously in nature and many fields which involve the solid-liquid separation. This paper employs the coupled computational fluid dynamics and discrete element method (CFD-DEM) to investigate the sedimentation process of non-cohesive particles, including the hindered settling stage and the deposition stage. Firstly, the coupled CFD-DEM model for sedimentation is validated by the hindered settling velocity at different solid volume concentrations of suspension (0.05~0.6). Two typical modes of sedimentation are also presented by the concentration profiles and the equal-concentration lines. Then, the comparisons between mono- and poly-dispersed particle system are detailed. In the sedimentation of the poly-dispersed particle system, the segregation phenomenon is simulated. Furthermore, this segregation effect reduces with the increase of the initial solid concentration of suspension. From the simulations, the contact force between every pair of particles can be obtained, hence we demonstrate the "effective stress principle" from the view of the particle contact force by giving the correspondence between the particle contact force and the "effective stress", which is a critical concept of soil mechanics. We also demonstrate the effective stress principle from the view of the contact force acting on particles. Moreover, the deposition stage can be simulated by CFD-DEM method, therefore the solid concentrations of sediment bed on different conditions are studied. Based on the simulation results of maximum solid concentration and the theory of sedimentation, this paper also discusses a method to calculate the critical time when sedimentation ends of two typical modes of sedimentation.