Demonstration of secondary currents in the pressure-driven flow of a concentrated suspension through a square conduit.

The existence of secondary flows in the pressure-driven flow of a concentrated suspension of noncolloidal particles through a conduit of square cross section under creeping flow conditions is confirmed experimentally. This Letter lends support to the idea that secondary currents, rather than shear-induced migration, may actually be the dominant mechanism that determines particle distribution in noncolloidal suspension flows through nonaxisymmetric geometries. This work also establishes that coextrusion of two concentrated suspensions through nonaxisymmetric geometries with a stable suspension-suspension interface is not possible, except in special situations.