The kinetics of flowing dispersions: I. Concentrated suspensions of rigid particles

Abstract

In the viscous flow regime the velocity profiles of dilute suspensions of rigid spheres in Newtonian liquids undergoing Couette or Poiseuille flow were found to be identical with those predicted by the theory with no particles present. At concentrations low enough so that the formation of triplets and higher order multiplets could be neglected, a given sphere exhibited fluctuations about a fixed mean radial position. The measured distribution of lateral displacements agreed with a theory based on rectilinear approach and recession of colliding pairs, whereas the time average radial displacements were twice the predicted values. On increasing the concentration partial plug flow developed in the tube with a central core in which the particles traveled with identical velocities without rotating and at fixed radial positions. Outside this central core the particles described irregular paths which, however, were reversible with respect to translation and rotation when the direction of flow was reversed. The concentration profiles were found to be uniform over prolonged periods of flow, and the suspensions showed Newtonian behavior. The phenomena, many of which were similar in suspensions of rods and discs, were shown to result from a wall effect predicted by Vand and were not manifestations of non-Newtonian behavior.