Impeller Systems

This chapter presents the logic required to achieve the best impeller system design. It delves into a bit of (qualitative) reaction engineering and then a bit of history. The chapter lists the major steps to impeller system design: choose number of impellers, choose placement of impellers, choose type(s) of impellers, choose power split or distribution, and choose D/T and shaft speed. Direct shear created by the impeller system is not the main source of shear damage. Instead, rupture of small bubbles at the liquid surface does most of the damage, as the shear rates in a rupturing film may be 100 000 or more times those produced by an agitator impeller. If the bubble size corresponding to the threshold of damage is known, it is possible to use CFD techniques to predict a bubble size distribution, which could be very helpful.