Representative shear rate for particle agglomeration in a mixing tank

Abstract

Polystyrene particles were dispersed in glycerol solution containing sodium chloride. The orthokinetic agglomeration process of the particles was observed in a mixing tank agitated by a six-blade Rushton turbine. It is found that the median diameter of agglomerates was initially increased and asymptotically approached a constant value. Bimodal particle size distributions were obtained within all of the experimental conditions and the stable size of produced agglomerates was independent of the rotational speed of the impeller. On the other hand, the amount of produced agglomerates was increased as the increase in the rotational speed of the impeller. Considering the experimental results, the population balance equation of a mathematical model to describe the evolution of the agglomerates was simplified. Then a representative shear rate taking into account the shear history of individual particles was proposed and its applicability was evaluated. It is showed that this shear rate is useful to predict agglomeration behavior of particles and a conventional representative shear rate in a mixing tank is overestimation.