Analysis and prediction of cluster formation

An experimental and theoretical analysis of the interaction of titanium dioxide particles during coagulation was performed, using laser light dynamic scattering (LDS) and both von Smoluchowski and reversible coagulation approaches. For cluster formation, different initial particle numbers and different shear rates were investigated and the experimental data were fitted to a mathematical model based on aggregation and disaggregation processes. The primary particle size was less than 1 micrometre, but in all cases the LDS information showed that primary clusters of 3.5 micrometres were rapidly formed, which then went on to cluster further to provide larger aggregates. Hence, the modelling approach was one of cluster-cluster aggregation and disaggregation, rather than primary particle aggregation

The Structure of Bidisperse Suspensions at Low Reynolds Numbers

We present a simulation technique for the direct simulation of the motion of spherical particles suspended in fluids at low Reynods numbers. We use this method to simulate bidisperse suspensions at varying size ratios of the suspended spheres and compare to analytic results of Batchelor for the low concentration regime. We find that the pair correlation functions indicate that three body hydrodynamic e#ects are significant even at volume fractions of # = 0.01 and lead to a decrease of the settling velocity of the involved particle species. In order to describe the time evolution of the concentration profiles in a suspension that settles into a condensed sediment layer from an initially well-mixed state, we propose an advection-di#usion model. The functional forms of the required hindered settling and hydrodynamic di#usion terms are chosen to describe not only our simulation results but also match other experimental results and asymptotically known theoretical predictions...