Particle-fluid velocities and fouling in rotating filtration of a suspension

The flow of dilute suspensions in a rotating filter separator consisting of a rigid, porous, polyethylene cylindrical filter rotating within an outer cylindrical shell was studied using laser-based velocity measurement techniques. The centrifugal instability of the Taylor-Couette flow results in toroidal vortices stacked in the annulus. The velocity field of the particles is very similar to that of the fluid indicating that the vortical structure readily entrains particles. Profiles of the concentration of particles in the device show that the particles tend toward a concentration polarization layer near the porous inner cylinder due to the radial flow, but the concentration in the layer is reduced as the velocity gradient near the wall is increased. This steep velocity gradient is a consequence of the vortices in the flow redistributing the azimuthal momentum. The vortices also distribute the particles uniformly across the annulus between the porous inner cylinder and the outer shell. Particles typically form a thin cake on the inner cylinder due to the radial flow. However, there is a critical Taylor number, which is related to the rotational speed of the inner cylinder, above which the particles are swept off of the inner cylinder and resuspended in the vortical flow. (C) 2002 Elsevier Science B.V. All rights reserved.