An improved permeability model for fractal aggregates settling in creeping flow

Aggregates often have mass fractal properties and there is, therefore, considerable interest in the hydrodynamics of mass fractal aggregates. There is no appropriate model in the literature to account for the non-homogeneous permeability within mass fractal aggregates. The new model proposed treats an individual aggregate as a self-similar object made up of a settling swarm of permeable spheres which are themselves made up of a settling swarm of sub-spheres and so on to the level of primary particles. This staged approach makes appropriate use of the fractal description of the aggregate to account for non-homogeneous distribution of porosity and quantify the drag correction for flow through effects. It also allows the settling properties to be quantified for multiple level aggregate structures, such as those formed from microflocs or by restructuring.