Effect of Macroinstabilities in Single- and Multiple-Impeller Stirred Tanks

In this work, a simplified analysis of the features of macroinstabilities in stirred tanks is proposed. The experimental part of the study is based on the collection of time series acquired by pressure transducers placed on the tank wall. The measurements are not invasive, because of the probe position, and they can be easily performed in laboratory and in industrial equipment, due to the instrumentation characteristics. With respect to previous investigations, the experimental analysis is extended from Rushton and pitched-blade turbines to Chemineer BT-6 and the effect of multiple impellers (MIs) is considered. The MI presence, frequency, velocity, and strength are obtained from the analysis of the collected pressure time traces; simplified correlations for their prediction are proposed. Finally, the dynamic pressure components associated to the MIs are presented, and a simplified model to assess their importance with respect to those produced by the blade passage frequency is suggested.