Gravity-driven flow of concentrated suspensions (solid volume fraction $\varphi >0.50$) of non-Brownian spherical particles through a channel contraction at low Reynolds number is studied experimentally. The abrupt change in the flow area at the contraction forms distinct shear-rate regions having different fluid pressures, which are related to the concept of particle pressure. A model involving particle pressure variation coupled to a Darcy-like behavior for the fluid captures the phenomenon of “self-filtration,” in which the effluent material has lower solid fraction than the input suspension. For $\varphi \doteq {\varphi }_{crit}\approx 0.58$, under added load from a weighted piston, the flow periodically alternates between fast and slow motions.

• Received 9 November 2009

DOI:https://doi.org/10.1103/PhysRevE.82.010402