Free settling of aggregates with mixed statistics

The free settling model is presented for aggregates of multilevel structure. Primary aggregates, formed by primary particles, join together to produce larger objects, which are treated as monomers for bigger clusters until the final aggregate is obtained. The objects at each structural level have specific size and the fractal dimension. The obtained aggregate free settling velocity normalized by that for primary particles can be expressed as dependent on the ratio of their sizes and the total number of primary particles. Some experimental data are quoted to support the obtained dependence. They are that for kaolin flocs of two-level structure measured by light-scattering technique and free settling test.