Effects of Shape of Impeller, Baffle and Draft Tube on Gas Enfoldment in the Stirred Tank

Abstract

Impeller speeds at which gas enfoldment from the free liquid surface and stationary dispersion of enfolded bubbles began were measured by changing various factors such as the shape of the impeller, the number of baffles, the impeller location, the liquid depth, the tank diameter and surface tension and by installing a draft tube. For all impellers investigated (six-bladed disc turbine, four-bladed pitched fan turbine, three-bladed propeller), the installation of baffles and the increase of their number raised the impeller speed for gas enfoldment. For the condition of four baffles, the following expression was obtained: [Equation Ommited] where the values of A, c and d depended on the shape of the impeller. For impellers other than the disc turbine, installing the draft tube and lengthening it raised the impeller speed for gas enfoldment. Moreover, simultaneous installation of baffles and draft tube was found to raise the impeller speed for gas enfoldment for all impellers. © 1985, The Society of Chemical Engineers, Japan. All rights reserved.