Particle Motions in Non-Newtonian Media. II. Poiseuille Flow

Abstract

The behavior of rigid and deformable particles suspended in pseudoplastic and elasticoviscous liquids undergoing tube flow was studied. The velocity profiles were more blunted than those obtained for Newtonian fluids and, as in Couette flow, the measured angular velocities of rigid spheres, rods, and discs were in accord with the theory for Newtonian liquids. There was also a drift in the orbit of the cylinders to limiting values corresponding to minimum energy dissipation in the flow. In elasticoviscous liquids, rigid particles migrated across the planes of shear towards the tube axis whereas in pseudoplastic liquids, the opposite was observed, rigid spheres actually coming in contact with the wall. The lateral migration of deformed liquid drops in elasticoviscous fluids was, as in Newtonian systems, towards the tube axis whereas in pseudoplastic liquids the drops attained an equilibrium position between the tube wall and axis. An accumulation of rigid spheres behind an advancing suspension-air meniscus was observed in elasticoviscous media at all initial volume concentrations, the rates of accumulation increasing with flow rate and particle size. In the pseudoplastic fluids, however, there was a dilution at concentrations less than 10% followed by an accumulation at higher values but the rates of accumulation decreased with increasing flow rate and particle size. As in the Couette flow of non-Newtonian suspension, it was not possible to interpret the observed radial migration of the particles in terms of the known rheological properties of the suspending fluids.