A simple model for power consumption in gassed and boiling stirred vessels

The aim of this work is to investigate the influence of the main geometrical and hydrodynamic characteristics of gas-liquid stirred tanks on the ventilated cavities forming at the rear of impeller blades and the effect of their size on power consumption. The experimental part of the work was carried in a standard baffled vessel, mechanically stirred with a Rushton turbine. The influence of the sparger diameter on the cavity dimensions and the power consumption was evaluated first, using two different gas spargers. The experimental data confirm that the gas distributor plays an important role on the interactions between the gas-liquid mixture and the impeller. On the modeling side, a simplified correlation to predict the cavity size is developed, that is based on the analogy with the phenomenon of ventilated cavity formation at the rear of vehicles traveling through water. After testing its consistency by adopting available literature data, the correlation is implemented in a mechanistic model for evaluating the power consumption for aerated modern turbines as well as stirred boiling systems, and acceptable predictions are obtained. (c) 2008 American Institute of Chemical Engineers.