Liquid migration in shear thickening suspensions flowing through constrictions

TL;DR

This study investigates how shear-thickening suspensions undergo liquid migration during extrusion through constrictions, revealing a universal concentration behavior dependent on flow rate and die size, explained by a coupled shear thickening and solvent permeation model.

Contribution

It introduces a quantitative model coupling shear thickening behavior with solvent permeation to explain liquid migration during suspension extrusion.

Findings

Extrudate concentration remains steady and independent of initial conditions.

Concentration varies with flow rate and die size, collapsing onto a universal function.

Model accurately predicts the onset of liquid migration in shear-thickening suspensions.

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 $\phi_c$, independent of time or initial concentration. This concentration $\phi_c$ varies with volumetric flow rate $Q$ and die radius $r_{\rm d}$, but at low $Q$ collapses onto a universal function of $Q/r_{\rm d}^3$, 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.