A numerical investigation into the influence of mixing on orthokinetic agglomeration

The scale-up behaviour of orthokinetic agglomeration in a 1, 10, 100 and 1000 liter vessel was investigated numerically, using constant Re-number, constant power input and constant impeller tip speed as scale rules. It was found that scale-up at constant <(<epsilon>)over bar> yielded the most constant results. At increasing volume, the influence of the macroscopic mixing time scale could be seen. In practice, laboratory scale experiments to determine agglomeration rate constants are carried out in stirred tanks of 1-10 liter. The results of this study indicate that this flow system exhibits too high turbulent intensities for agglomeration to occur readily. This is consistent with the experimental observation that small stirred tanks agglomerate badly, while large reactors do agglomerate. Laboratory scale stirred tanks will therefore be less suited for measuring these kinetic data.