Liquid migration in shear thickening suspensions flowing through constrictions

Abstract

Dense particulate suspensions often become more dilute as they move downstream through a constriction. We find that as a shear-thickening suspension is extruded through a narrow die and undergoes such liquid migration, the extrudate maintains a steady concentration ${\varphi }_c$, independent of time or initial concentration. This concentration ${\varphi }_c$ varies with volumetric flow rate $Q$ and die radius $r_{\mathrm{d}}$, but at low $Q$ collapses onto a universal function of $Q/r_{\mathrm{d}}^3$, a characteristic shear rate in the die. We explain quantitatively the onset of liquid migration in extrusion by coupling a recent model for discontinuous shear thickening and the `suspension balance model' for solvent permeation through particles.

5 pages, 5 figures