Understanding the effects of particle properties and particle-scale flow on suspension rheology

Abstract

Dense suspensions of solid particles immersed in a liquid are ubiquitous in industries. Understanding the rheology of dense suspensions plays an important role in improving industrial processes. In this thesis, the coupling of the Lattice Boltzmann Method (LBM), a class of computational fluid dynamics (CFD) methods for fluid simulation, and the Discrete Element Method (DEM), an effective numerical method in the analysis of granular systems, have been employed to simulate the non-Brownian dense suspensions. Such LBDEM simulations can capture the detailed flow field in the particle level and reveal the effect of the interactions between background fluid and particles.

We conduct DEM simulations of a binary model system composed of frictional and frictionless particles (Chapter 4) and investigate the relationship between the jamming volume fraction of dense suspension and the fraction f of frictional contacts, which is determined by the fraction of frictional particles. By comparing our data with simulations of shear thickening suspensions, which introduce a transition between frictional and frictionless contacts by the Critical Load Model (CLM), we show that the Wyart-Cates model of shear thickening is incomplete. The shear-thickening behaviour is then successfully captured by LB-DEM simulations of dense suspensions under simple shear (Chapter 5). The difference between LBDEM and DEM simulations of suspensions can be minor in terms of the bulk rheology because the averaged velocity fields under simple shear are similar for these two simulation approaches. The third part is the LBDEM simulations of pressure-driven flow in the square channel (Chapter 6), where interactions between fluid and particles are not negligible and cannot be captured by DEM simulations. We capture the shear-induced migration of suspensions in the channel and look into the effect of friction in the migration process. With detailed information of the fluid phase from LBM and the solid phase from DEM, we examine the suspension balance model for different volume fractions and friction coefficients. These results can serve as a database for the further theoretical study of pressure-driven flow.