MECHANISM OF SHEAR AGGREGATION

A model of shear aggregation is proposed using the ideas of fractal geometry of aggregates. It is shown that the aggregate structure depends on the constituent clusters parameters-their sizes and fractal dimensions. Generally the fractal dimension of formed aggregate increases with the ratio of sizes of constituent clusters. As a result of the collision sequence the aggregate size distribution is formed, as well as the effective fractal dimension of the population. The width of the aggregate size interval is related to the fractal dimension of the cluster population. The time decrease of aggregation rate is interpreted as caused by progressive exclusion of part of the cluster population from the mutual aggregation. At the end of aggregation all aggregates that would be produced are too weak to sustain the hydrodynamic stresses caused by shear. The model is successfully verified experimentally with no insert of adjustable parameters, so the mechanism of shear aggregation may be regarded as better understood.