(274c) Simulating the Flow of Concentrated Suspensions

Concentrated suspensions are ubiquitous in technologies ranging from personal care products to construction, and their flow response can be complex, exhibiting shear thinning (decreasing viscosity) and shear thickening (increasing viscosity) in different shear-rate regimes. Attractive forces between particles can cause a yield stress, requiring a minimum applied stress to induce flow. Concentrations approaching maximum packing can exhibit re-entrant behavior and discontinuous shear thickening, in which the shear viscosity suddenly increases by orders of magnitude. We have simulated the flow of concentrated suspensions of both Brownian and non-Brownian spheres in a Newtonian suspending fluid at the particle level by taking into account the apparent breakdown of classical fluid lubrication and the onset of particle-particle friction when applied stresses force flowing particles together. A simple friction model is sufficient to capture the observed physical behavior and provides an avenue to the formulation of macroscopic models for processing flows, but the breakdown of the continuum assumption implied by particle contact points to a need for exploration of the molecular nature of the tribological interactions.

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