AGGREGATION AND BREAKUP OF PARTICLES IN A SHEAR-FLOW

An experimental study was carried out to investigate aggregation and b reakup of particles in a Couette flow system with the inner cylinder r otating at constant speed. Experiments were conducted with monodispers e and polydisperse suspensions at different particle volume concentrat ions. Depending on both the shear stress and the particle concentratio n, three different regimes were found. In the first regime, when the c oncentration is less than a critical value, the final diameter of the aggregate is independent of concentration and depends only on the shea r. When the concentration is higher, two new regimes are identified, w ith the final diameter of the aggregate depending on both shear stress and particle concentration. Also, the transition between these two re gimes corresponds to the transition from laminar to turbulent flow. In addition, the final diameter of the aggregates in the turbulent flow regime is independent of the size of the primary particles and results to be is controlled by the Kolmogorov length scale. On the contrary, in the laminar flow regime the final diameter of the aggregates shows a light tendency to decrease as the diameter of the primary particles increases. (C) 1997 Academic Press.