INFLUENCE OF INTERPARTICLE INTERACTIONS ON BLOCKED AREAS AND DESORPTION DURING PARTICLE DEPOSITION TO GLASS IN A PARALLEL-PLATE FLOW CHAMBER

In this paper we measured the influence of interparticle interactions between flowing and adhering particles on initial deposition rates, blocked areas, and residence time dependent desorption during deposition of polystyrene latex particles to glass. The initial deposition rates increased linearly with particle concentrations in suspensions as expected from theoretical mass transport calculations. Deposition efficiencies of 0.78 and 0.62 were obtained for wall shear rates, G, of 15 and 50 s(-1), respectively. Blocked areas, A(1) expressed as the number of particle cross sections, gamma, decreased from initially high to low values (A(1,G=15) = 10 and A(1,G=50) = 18, at infinite particle concentration) as a function of the particle concentration. This decrease in blocked area with particle concentration was explained as a consequence of the increased backscattering of flowing particles colliding with adhering particles. Backscattering due to collisions between flowing particles is obviously more frequent at higher Concentrations. Blocked areas, calculated using pair distribution functions, corresponded well with those obtained from deposition kinetics. Initial desorption rate coefficients, beta(0) ranging from 0.3 x 10(-3) to 2.0 x 10(-3) s(-1), increased linearly with particle concentration in suspension due to an increase in the number of collisions between adhering and flowing particles per unit time. The final desorption rate coefficients, beta(infinity,) ranging from 0.002 x 10(-3) to 0.01 x 10(-3) s(-1), and the relaxation time, 1/delta, of the desorption rate coefficient, ranging from 50 to 1000 s, decreased as a function of the particle concentration because, as the effective interaction potential minimum is not the same for each adhering particle, weakly adhering particles will be removed first. The effective interaction potential minimum decreases as a function of shear rate due to increased hydrodynamic drag and lift forces resulting in higher desorption rate coefficients at higher shear rates.