Kinetics of particle deposition in the radial impinging-jet cell

A detailed description of the flow distribution in the radial impinging-jet (RIJ) cell was attained by solving the governing Navier-Stokes equation nu merically. It was shown that for tangential distances r/R < 0.25 the flow c onfiguration in the vicinity of the solid interface approached the stagnati on point flow with the perpendicular velocity component independent of the radial distance. The intensity of this quasi-stagnation point flow, governe d by the a parameter, was calculated numerically as a function of the Reyno lds number. It was also found that the flow pattern in the RIJ cell resembl ed the flow occurring near a sphere immersed in a uniform flow. Knowing the fluid velocity field the convective diffusion equation was formulated. Thi s equation, describing a two-dimensional transport of particles, was solved numerically by using the implicit finite-difference method. In this way th e particle deposition rate for the low coverage regime (initial flux) can b e determined for various parameters such as particle size, Reynolds number, distance from the stagnation point, etc. The validity of the theoretical p redictions was verified experimentally using direct microscope observation of polystyrene latex particles of size 0.87 mum. The initial flux near the stagnation point was measured as a function of Reynolds number and ionic st rength of the suspension. The dependence of the local mass transfer rate on the distance from the stagnation point was also determined experimentally. This enabled one to estimate the error associated with indirect (optical) measurements of protein absorption in the RIJ cell. A good agreement betwee n predicted and measured flux values was found, which validates the applica bility of the numerical solutions of the flow field and mass transfer in th e RIJ cell. It was suggested that by measuring the initial flux for colloid particles microscopically one can determine in a direct way the local mass and heat transfer rates for the impinging-jet configuration used widely in practice. (C) 2001 Academic Press.