Influence of geometry and angular velocity on performance of a rotating disk filter

The influence of internal geometry and angular velocity on the performance of a rotating-disk filtration device is described. This module consists of a disk rotating at speeds up to 2,000 rpm inside a cylindrical housing equi pped with a fixed flat membrane. The test fluid was a calcium carbonate sus pension (4.7-mu m mean particle diameter), and the membranes were in nylon (0.2-mu m mean pore diameter) and PVDF (0.1 and 0.18 mu m). The shear stres s on the stationary membrane in the laminar boundary-layer regime was estim ated from a similarity solution, and in the turbulent regime from the frict ion coefficient for a flat plate. Several inlet and outlet configurations w ere tested. The permeate flux was independent of the axial gap (disk to mem brane), but increased when the radial gap (from disk to housing) was raised from 2 to 5 mm. The inviscid fluid core in the axial gap was observed to r otate at 42% of angular velocity with a smooth disk. This factor rose to 64 % when the disk was equipped with small vanes. Fouling was limited to the c entral part of the membrane at 1,500 rpm and disappeared completely for a d isk equipped with vanes. Permeate fluxes were consistently much higher than in classic cross-flow filtration.