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

Deposition of negatively charged polystyrene particles on quartz in a parallel (PP) and stagnation point (SP) flow chamber is compared at similar Peclet numbers for different ionic strengths and pH values. Initial deposition rates have been derived from the experiments and numerically calculated from the convective-diffusion equation. An upper limit for deposition, neglecting interaction forces, is obtained from the Smoluchowski-Levich solution of the convective-diffusion equation. Initial deposition rates were on average 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 rates and blocked areas were observed more strongly in the SP flow chamber than in the PP flow chamber, while the dependence of deposition on pH was absent in both flow chambers. Desorption probabilities of the polystyrene particles on the quartz surfaces were close to zero. The experimental reproducibilities obtained in the SP flow chamber were superior compared with those found in the PP flow chamber. Analysis of error propagation for the SP data could account for the final reproducibility observed, but for the PP data the final reproducibility could not be accounted for on the basis of system variabilities and enumeration errors, leading to the conclusion that mechanistically deposition in the PP flow chamber depends more on statistical processes, like diffusion and collisions between flowing and adhering particles, while deposition in the SP flow chamber is more interaction controlled.