Hydrodynamics of aggregated media

The hydrodynamic properties of fractal aggregates are evaluated by modeling them as porous media governed by the Brinkman equation. The dimensionless internal permeability of an aggregate is determined as dependent on the fractal dimension. Replacing real aggregates hy impermeable spheres of a size chosen such that tile overall permeability remains unchanged, the fractal dimension dependence of the structure factor is deduced. The obtained result is used for the normalization of the size and the volume fraction of aggregates in the system. It is shown in this way that the hydrodynamic behavior of aggregated media over wide ranges of concentration and fractal dimension can be successfully approximated by the methods of hard sphere system hydrodynamics. Other applications of the obtained result are mentioned and discussed. (C) 1996 Academic Press, Inc.