Dispersion of a suspension plug in oscillatory pressure-driven flow

We investigate the dispersion of finite lengths of concentrated suspended particles, or suspension plugs, in a microcapillary as they are sheared in an oscillating pressure-driven flow. In the experiments, plugs of neutrally buoyant, noncolloidal particles (90-mu m mean diameter) suspended in viscous fluid at low and high concentrations are observed for various values of applied strain of this cyclic shearing flow. No significant increase in the overall plug length is seen near the centerline after numerous cycles. However, significant streamwise particle migration was observed near the walls of the capillary, becoming more pronounced with increasing strain amplitude. Related numerical simulations for a suspension plug sheared in a planar channel show similar results and elucidate the dynamics for this strongly inhomogeneous flow and the anomalous particle fluxes that develop.