Adding active particles for overall aggregation in a mixing tank: a computational study

In order to achieve flocculation in a dense agitated solid-liquid suspension of nonaggregating particles, we explore scenarios where we add a limited amount of aggregative (ie, active) particles that can bind the nonaggregative particles. The performance of this process hinges on the competition between mixing (spreading the active particles over the flow volume) and aggregation among the active particles, with the latter reducing their effectiveness. The research has been conducted in a computational manner: direct simulations of transitional flow in a mixing tank (at an impeller-based Reynolds number of 4000) are two-way coupled with the dynamics of a collection of spherical, equally sized particles that are given specific aggregative properties. The overall solids volume fraction is 10%. A small fraction of all solid particles (5.8%) is active. Aggregation is quantified by means of the average coordination number as well as the aggregate size distribution. The way the active particles are released in the tank volume has a significant effect on the overall levels of aggregation, specifically for active particles with a strong aggregative force.