(83g) Apparent Suspension Viscosities Found By Computationally Simulating a Couette Viscometer

We report the results from direct numerical simulations of the flow of slurries in a Couette viscometer. We used a lattice Boltzmann technique with an immersed boundary model for studying the fully resolved response of a slurry to a simple shear as in a Couette viscometer. The slurries consisted of a Newtonian liquid carrying mono-sized spherical solid particles in the range 150-300 micron, up to solids volumes as high as 50%. We used either short-range spring forces or lubrication forces to deal with particles approaching each other closer than the lattice (grid) spacing. We computed the relative apparent viscosity for several shear rates and particle concentrations, and discuss the effects of these variables on particle rotation and cluster formations. The apparent viscosities increase with increasing particle Reynolds number (shear thickening) and solids fraction. As long as the particle Reynolds number is low (0.1), the computed viscosities are in good agreement with experimental measurements as well as with theoretical and empirical equations. To mimic the flow behaviour of iron oxide particles in a caustic medium, we added electric double layer forces to the simulation to model the pertinent repulsion between the particles. We report on the effect of pH in the range 9 through 12 and of the Debye length on spatial particle structures, resulting in a reduced apparent viscosity at higher solids volume fractions.