Understanding the rheology and dynamics of solid-in-liquid suspensions

Abstract

The transport and flow behavior of solid-in-liquid suspensions is an important area of research in modern fluid mechanics, with profound implications spanning industrial processing, chemical manufacturing, and biological systems. This talk will explore the complex behavior and transport phenomena governing solid-in-liquid suspensions across a wide spectrum of particle concentrations. The fundamental framework systematically tracing how microscopic interactions scale up to dictate macroscopic flow properties will be presented. At the very dilute limit, the background flow field plays the dominant role in governing suspension dynamics, where hydrodynamic drag and single-particle mechanics dictate the rheology and dynamics. As the particle concentration increases into the dilute regime, the onset of interparticle hydrodynamic interactions introduces collective behaviors, including intriguing microstructural phenomena such as pattern formation, even though the flow behavior remains strictly that of the carrier fluid. With further increase in concentration, the strong influence of particle-particle and particle-wall interactions gives rise to a net flux of particles away from regions of high shear intensity. This phenomenon, known as shear-induced particle migration, will be evaluated through two primary constitutive modeling frameworks: the Diffusive Flux Model (DFM), which treats migration as a phenomenological diffusion process driven by shear-rate and viscosity gradients, and the Suspension Balance Model (SBM), which derives migration from the conservation of particle-phase momentum and anisotropic particle-phase stresses.  The talk will demonstrate how shear-induced migration manifests in complex geometries, altering velocity and concentration profiles. The practical implications of this phenomenon will be highlighted through its critical role in hemodynamics and blood flow behavior. Finally, the talk will address the experimental and computational rheology of very dense, shear-thickening suspensions, providing a physical look into the underlying mechanisms that drive both continuous and discontinuous shear-thickening transitions. To capture the physics of highly concentrated and dense regimes, the utility of Stokesian Dynamics (SD) simulations will be presented.