FLUX-CONTROLLING FACTORS IN CROSS-FLOW MICROFILTRATION OF DILUTE SLURRIES

The constant-pressure filtration characteristics in the crossflow microfiltration of dilute slurries are examined under various operating conditions, using a tubular ceramic membrane. On the basis of correlating a newly defined flux-controlling factor, a method for analysing both transient and steady filtration rates is studied. With a membrane having much smaller modal pores, much smaller than the size of the suspended solids, inspection of the crossflow filtration data points to a common feature: gradual reduction initially, followed by a substantially uniform value of filtration flux. The time dependence of the flux is represented by introducing a dynamic filtration coefficient, defined as the ratio of cake resistance in unstirred and stirred microfiltration, into the conventional Ruth filtration-rate equation. The dynamic filtration coefficient is related to a number of operational variables, in view of the fact that the final steady flux can be estimated as a power-law function of both the shear stress acting on the cake surface and the constant-pressure filtration coefficient. Positive agreement between calculations and experiments is confirmed for the filtration rate of slurries of polymethyl-methacrylate particles and baker's yeast.