MODELLING OF NON-STANDARD MIXERS STIRRED WITH MULTIPLE IMPELLERS†

Abstract

Little attention has so far been devoted to characterizing fluid-dynamic behaviour of multiple-impeller mixers which are often implicitly modelled as perfectly stirred tanks.

In the present paper a study is made of this type of equipment—stirred with four turbines; either six- or four-flat-blade disc turbines were used. Mean local concentration inside the mixers was measured and experimental pulse-response curves were compared with the theoretical curves corresponding to two one-parameter models (i.e., a cascade of ideal stages with backmixing and one-dimensional diffusion model) and to perfect mixing.

The results of both analyses show that both the one-parameter models considered represent the actual fluid-dynamic behaviour quite satisfactorily and the model of perfect mixing can be considered only as a first approach for macromixing modelling purposes.

Extensive investigation was then carried out in order to determine the dependence of the characteristic parameter of the stagewise model on operating conditions. Certain anomalies regarding situations where non-Newtonian fluids are used are also presented.

Notes

† Paper presented at the 7th CHISA congress, Prague, August 31-September 4, 1981.

Additional information

Notes on contributors

G. PASQUALI

Author to whom all corespondence should be addressed.