Mixing of Liquids in Large Tanks

Abstract

A 1.2 m diameter tank has been used to model the mixing process in large storage tanks equipped with side-entry mixers.Terminal mixing times have been measured as a function of impeller speed, impeller diameter, liquid depth and impeller angle. it is shown that the indicator method for measuring mixing times yields results which are dependent upon the molecular diffusivity of the materials employed. A mathematical model is presented which accounts for this effect, and some of it's predictions have been tested using a 70 mm diameter tank. It is shown that the conductivity method for measuring mixing times gives results which can be used for scale-up using the rule NϒD2 /Τ2 = Const., and this has been tested on a 31 m diameter tank. Measurements have also been made of fluid velocities using a hot film anemometer, and these are shown to be consistent with a simple boundary layer theory.