Deposition of particles in the impinging-jet cell for the high coverage regime

Particle deposition in the radial impinging-jet cell for the high coverage regime was studied theoretically and experimentally. A detailed description of the flow distribution in the cell was attained by solving the governing Navier-Stokes equation numerically. The macroscopic flow pattern was decomposed into simpler local flows. It was demonstrated that for tangential distances r/R > 0.5 the overall flow at the interface was dominated by the simple shear. The intensity of this flow was calculated numerically as a function of the Reynolds number and the distance from the cell center. Knowing the fluid velocity field the convective diffusion equation was formulated describing a two-dimensional transport of particles. As a result of nonlinearity of the boundary condition this equation was solved in an exact manner for low coverage only. For higher coverage, approximate methods were proposed exploiting the random sequential adsorption (RSA) approach. The validity of the theoretical predictions was verified experimentally using the direct microscope observation method and polystyrene latex particles of the size 0.87 mum. Particle coverage distribution was studied in detail as a function of the Re number governing the local shear rate. It was demonstrated that for low Re number (Re < 4) uniform particle monolayers of high coverage can be attained. On the other hand, for Re > 8 the particle coverage distribution became nonuniform as a result of the hydrodynamic scattering. This effect, leading to an apparent kinetic saturation of the surface at coverages of a few percents, was quantitatively interpreted in terms of the theoretical model. (C) 2002 Elsevier Science (USA).