The goal of this study is to enhance fundamental understanding of the flow of a concentrated suspension through an abrupt contraction-expansion. Contraction-expansion flows arise in such applications as materials processing or flow in the circulatory system. Measurements of the pressure distribution in concentrated suspension flows are rare, although very useful for comparison with other system properties, as well as for practical considerations such as pump sizing requirements. Of particular interest is the relationship of the particle concentration distribution, which can be spatially nonuniform, to the length of recirculating regions in the expansion and to the total pressure drop.

In this study, suspensions of neutrally buoyant, noncolloidal spheres in viscous, Newtonian liquids undergo steady, 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 and velocity profiles. Wall-mounted pressure transducers record the pressure drop across the contraction-expansion tube section. The effect of shear-induced particle migration on the concentration, velocity, and pressure fields in the system is investigated, and the role of particle and flow properties (e.g. particle volume fraction, particle size, flow Reynolds number, and inlet conditions) is examined. Comparison of experimental results with continuum model calculations can provide further insight into suspension flow behavior in a complex geometry. In addition, results on particle size separation obtained from a bimodal suspension will be presented.