Nonstandard Geometries Aspect Ratios Greater Than 1 and Multiple Impellers

6 Nonstandard Geometries Aspect Ratios Greater Than 1 and Multiple Impellers 

Cooke et al. (1988) reported mixing times for a range of multiple-impeller systems. They found the time increased very significantly but did not distinguish whether the increase was due particularly to the increase in height or the extra number of impellers. The equation that they gave for multiple Rushton turbines is similar to eq. (9-2)  

Cronin et al. (1994) showed by a decolorization technique Ihe staged mixing associated with radial flow Rushton turbines, and Otomo et al. (1993) showed similar results with radial flow hollow-blade turbines. The latter also used conductivity probes and found mixing times about twice as long as with a single impeller, with values close to the predictions of the equation of Cooke et al. (1988). 

Clearly, once mnltiple impellers are employed, particularly with aspect ratios significantly different from 1, the system becomes considerably more complex. Mixing times can greatly increase and the choice of impellers now can be very significant. 

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