Comparison of particle deposition in a parallel plate and a stagnation point flow chamber

Deposition of negatively charged polystyrene particles on quartz in a paral lel (PP) and stagnation point (SP) flow chamber is compared at similar Pecl et numbers for different ionic strengths and pH values. Initial deposition rates have been derived from the experiments and numerically calculated fro m the convective-diffusion equation. An upper limit for deposition, neglect ing interaction forces, is obtained from the Smoluchowski-Levich solution o f the convective-diffusion equation. Initial deposition rates were on avera ge 5 times higher in the SP than in the PP flow chamber, in accordance with theoretical results. Effects of ionic strength on the initial deposition r ates and blocked areas were observed more strongly in the SP flow chamber t han in the PP flow chamber, while the dependence of deposition on pH was ab sent in both flow chambers. Desorption probabilities of the polystyrene par ticles on the quartz surfaces were close to zero. The experimental reproduc ibilities obtained in the SP flow chamber were superior compared with those found in the PP flow chamber. Analysis of error propagation for the SP dat a could account for the final reproducibility observed, but for the PP data the final reproducibility could not be accounted for on the basis of syste m variabilities and enumeration errors, leading to the conclusion that mech anistically deposition in the PP flow chamber depends more on statistical p rocesses, like diffusion and collisions between flowing and adhering partic les, while deposition in the SP flow chamber is more interaction controlled .