(108h) Bimodal Vs. Monomodal Suspension Flows through An Abrupt Contraction-Expansion

The goal of this study is to understand the correspondence between concentrated bimodal and monomodal suspensions flowing through an abrupt contraction-expansion, which is a model geometry for materials processing operations. Previous studies have compared particle concentration profiles for monomodal and bimodal suspensions in unidirectional flows, emphasizing the differences between monomodal and bimodal suspension behavior. However, similar behavior can be identified clearly in the abrupt contraction-expansion flow, where distinctive particle concentration distributions for each bulk particle volume fraction form downstream of the expansion section.

In this work, suspensions of neutrally buoyant, noncolloidal spheres in viscous, Newtonian liquids undergo pressure-driven flow in an abrupt, axisymmetric 1:4 contraction-expansion. Nuclear magnetic resonance imaging (NMRI) is used to measure the steady-state particle concentration distribution and flow field. By adopting varied particle materials (i.e. rigid polymer vs. hydrogel) we can monitor distributions of small and large particles through the contrast in the spin-spin (T2) relaxation time among rigid solids, gels and suspending fluids. Results to date suggest that the large particle distributions observed in bimodal suspensions resemble those of monomodal suspensions of large particles with the same average steady shear viscosity.