THE VARIATION OF CROSS-FLOW FILTRATION-RATE WITH WALL SHEAR-STRESS AND THE EFFECT OF DEPOSIT THICKNESS

The crossflow filtration of magnesium hydroxide slurries is described. The pseudo steady state flux is shown to correlate with the wall shea r stress. A deposit of appreciable thickness builds up on the filter t ube, and the correlation improves when the deposit thickness is includ ed in the calculation of wall shear stress. A technique to deduce the deposit thickness from pressure measurement in a single filtering tube is described. The model has been tested using filter tubes with an un coated diameter of 4 mm and 14 mm filtering non-Newtonian slurries wit h solids concentrations ranging from 13% to 24% by volume. For particl es which can substantially penetrate a filter the wall shear stress mo del is shown not to apply, as the filter membrane is subject to intern al blocking, which severely reduces the filtration rate.