PARTICLE DEPOSITION ON PARTIALLY COATED SURFACES

The flux of colloidal particles to a collector surface depends on the fluid velocity field in the vicinity of the collector which, in turn, is affected by the presence of previously deposited particles. The hydrodynamic force exerted by the deposited particles on the fluid in a stagnation point flow was estimated from effective medium theory, using the so-called point-force theory, by solving a system of integral equations for various coating densities. The mass transfer equation, with appropriate boundary conditions, was solved for the disturbed flow field, under the assumption that hydrodynamic and van der Waals interactions between particles and the collector cancel each other (Smoluchowski-Levich approximation). Colloidal interactions between deposited and flowing particles have a significant influence on blocking. It has been shown that for low coating densities the blocking is more pronounced for high Peclet numbers. However, for large coating densities the effective flux is higher for large Peclet numbers because intensive flow pushes more particles towards the collector surface. Since the flux to partially coated surfaces depends on the colloidal interactions between particles, the magnitude of these interactions can, in principle, be determined from the rate of particle deposition on such surfaces, which can be readily measured experimentally.