Towards A Digital Twin of the Flocculation Process

In various environmental and engineering applications, small particles suspended in fluid aggregate to form flocculate particle clusters. These particle aggregates can be observed in the smoke from a fire, or in the sediment deposits of a river delta. The shape and size of these particles directly influence their behavior. For example, the shape and size of soot particles determines how quickly they settle after an explosion.

 

The formation of the aggregate particles begins with smaller sub-particles of roughly the same size, called monomers. The monomers join with each other to form dimers which then join, and so on until the aggregate particle cluster is formed. The monomers and flocs come together by Brownian motion and turbulent shear. To classify the aggregate particles, they will be organized by their number of monomers and their fractal dimension. The number of monomers determines the size, and the fractal dimension describes the shape of the particle, with values of 1.0, 2.0, and 3.0 corresponding to a linear chain, a plane, and a sphere of monomers, respectively.

 

The current issue with understanding these flocculate particles comes from the oversimplification of their shape. Presently, the general approach is to treat the aggregates as spheres, regardless of their actual shape. This is an issue for several reasons. Considering the shape of the floc is essential to understanding the hydrodynamic force and torque exerted on it by surrounding flow, such an oversimplification will lead to inaccuracies. For example, the simplification method cannot distinguish between the force on a linear chain of flocs aligned with the flow and one that is perpendicular to it. Additionally, it cannot predict the torque on the floc and the resulting motion. Lastly, it does not account for the fact that certain hydrodynamic forces experienced by the flocs can be strong enough to break them apart.