Advances in Water Treatment and Enviromental Management

FOULING PHENOMENON IN CROSS-FLOW MICROFILTRATION PROCESSES 175hydrodynamical parameters are obtained by repeating measurements for the sameexperimental conditions when increasing porous tube length.Fig. 1: Experimental setup. Silicon oil flow (v=50 cSt) in a ceramicporous tube (L=.5m,D i =3.10 -2 m, e=10 -2 m, K=10 -12 m 2 ) with wall suction2.2 ResultsThe bulk numerical model is applied in order to predict the evolution of the hydrodynamicalfield for fixed crossflow filtration conditions.Computed pressure variations for a porous tube are compared to experimental data obtainedfor increasing filtration flux (Fig. 2). The figure shows good agreement between computed andmeasured values. Numerical results have been corrected in order to take into account theover pressure drop due to porous wall of the tube when Re w =0.Fig. 2: Evolution of the dimensionless pressure as a function of Re wThe numerical work has been developed for the special case of flow in a dead ended poroustube with wall suction (SCHMITZ 1989). Computed pressure variations are compared toexperimental data of Quaile and Levy to validate the model. Our model was performed topredict axial pressure variations for backwashing in membrane separation processes usinghollow fibers with an external membrane skin.2.3 DiscussionIn the real case of water crossflow filtration we have to take into account a dilute suspension ofparticles instead of a single fluid phase. The experience proves fouling of membranes duringthe filtration process leading to a decrease yeld. A study of the flow at microscopic scale performedby particle trajectories analysis shows conditions under which particles deposit on the porouswall and lead to the formation of a fouling cake (SCHMITZ, GOUVERNEUR, HOUI 1989).In order to take into account the changing boundary conditions at the interface between fluidand porous media due to the formation of a cake, it seems very important to characterize thestructure of the deposit.Parameters such as the permeability and the thickness of the cakeare obtained by modelling the formation of a cake consisting of spherical particles.3. SIMULATION OF DEPOSIT FORMATIONIn membrane separation process concerning water purification, surface deposits we canindentify consist generally of solid micronic particles, colloidal objects and macromolecules.