Hydrodynamics of permeable aggregates in differential sedimentation

A Computational Fluid Dynamic (CFD) tool was used to evaluate the role of aggregate porosity on aggregate collisions due to differential sedimentation. This modeling study shows the influence of the hydrodynamics of porous aggregates on the rectilinear aggregation rate constant (βDS) for differential sedimentation. Porous aggregates are represented as homogeneously permeable spheres. Results are summarized in terms of a correction factor to the rectilinear collision kernel that expresses the degree to which flow around aggregates approaches the curvilinear case. The functional form of aggregate interactions extracted from these simulations is well represented by a previously developed analytical expression. It was found that with increasing aggregate permeability, there was a subsequent increase in the collisions and, therefore, the collision rate constant. This increase in the number of collisions of permeable aggregates by an order of magnitude, compared to solid spherical aggregates represented by a curvilinear fluid trajectory conceptual model, shows the importance of considering the permeability of aggregates in predicting the outcome of particle aggregation modeling.