The behaviour of gas—liquid mixtures near Rushton turbine blades

The flow in the impeller region of an agitated tank dispersing gas in liquid has been studied using a rotating TV camera and fixed still and high speed ciné cameras. The roll vortices which form behind the horizontal edges of the blades continue as trailing vortices out into the main volume of the tank. Gas bubbles are captured by the centrifugal fields of these vortices and often form stable cavities centered along the vortex core lines. Dispersion occurs primarily as a result of the turbulent closure of the tip of the cavity, when small bubbles are broken off from the main mass of gas. Gas bubbles passing through the impeller region are much more likely to be coalesced—or at least agglomerate—with these cavities than to undergo rupture by the distortion mechanisms that have usually been envisaged.