Aggregate formation and collision efficiency in differential settling

A new method of application of Stokesian dynamics, which can efficiently simulate movements of up to 500 particles with interparticle interactions in reasonable computational times, has been developed for the purpose of investigating particle–cluster aggregation in aqueous systems. The method is applied to monodisperse non-Brownian spherical particles aggregating in differential settling, while repulsive colloidal interaction is presumed to be negligible, so that a minimum separation distance can represent the attractive van der Waals force. The final aggregates formed by this algorithm, composed of 300 primary particles, have a common fractal dimension of ∼2.0. The computed collision efficiency, defined as the product of a global and a capture efficiency, is about 5.77×10 −3. This value is significantly larger than the collision efficiency of primary particles colliding with an impermeable solid sphere of the same size as the aggregate, illustrating the important interplay between the permeability and the formation of aggregates.