THE EFFECT OF INTERFACIAL INSTABILITIES IN A STRATIFIED RESUSPENSION FLOW ON THE PRESSURE LOSS

This study investigates the stability of a laminar, cocurrent flow of a concentrated suspension below a clear fluid layer in a plane, horizo ntal channel. The suspension is treated as a Newtonian fluid with effe ctive density and viscosity dependent on the particle concentration. I n such cases, the flow problem resembles the stratified flow of two di fferent superposed fluids, which is well known to be unstable to long interfacial waves. The evolution equation for long interfacial waves i s derived by employing a method of multiple time scales and a regular perturbation technique. In this study, the particle concentration with in the suspension layer is a function of the local height of the pertu rbed interface. A wall slip boundary condition for the suspension is e mployed at the bottom wall of the channel. The evolution equation is B urgers' equation, which predicts the behavior of an initial disturbanc e. The variable particle concentration affects the stability of the fl ow. For a small ratio of clear fluid to suspension layer thickness, an unstable region exists if the Froude number is below a critical value . Favorable density stratification stabilizes the flow. Finally, it is shown that interfacial waves modify the pressure loss in the channel, which is in agreement with an earlier experimental observation. (C) 1 998 American Institute of Physics. [S1070-6631(98)03111-0].