Coagulation in a shear field generated by stirring in a cylindrical vessel

Abstract

The coagulation of aqueous ZnO dispersions is investigated at various shear rates, in a shear field generated by stirring in a cylindrical vessel, and at different ~" potential values. Laser Doppler anemometry measurements permitted the construction of a model of the shear field by which average shear rates could be calculated. At low shear rates (~<200 sec-~), the experimental capture efficiencies are independent of the ~" potential (-20 ~" > -3 2 mV). At larger shear rates, the capture efficiencies rise with increasing -~, if the absolute value of the ~-potential is ~<30 mV, due to inertial pseudoforces. These are more effective for irregular than for spherical particles, probably because the penetration of the last liquid film between two particles is easier at edges than at smooth surfaces. This effect, however, can be counteracted by electrostatic repulsion.

Modeling Orthokinetic Coagulation in Spatially Varying Laminar Flow

“…A third method treated each volume element as a separate batch reactor and a volume average of the population size class balance was subsequently obtained. The modeling of independent volume elements was considered due to the hypotheses of several prior researchers (28)(29)(30). These previous researchers suggested that dividing the flow domain into regions of nearly equal flow parameters (strain rate, velocity gradient, or energy dissipation) would yield improved coagulation modeling results.…”

Surface charge and coagulation of aqueous ZnO dispersions

“…Electrokinetic and coagulation rate measurements were performed in dilute suspensions (3.2 mg in 25 ml), prepared as described previously (10). Adjustment of the pH in the initial suspension was much more rapid for preheated ZnO than for ZnO a.r.…”

Zeta potential and coagulation of ZnO in alcohols

“…Coagulation rates were determined in a stirred cylindrical vessel using a stirring speed of 700 rpm [9,14].…”