Sauter mean bubble sizes and size distributions on a number basis were determined photographically in the neighbourhood of a Rushton turbine impeller. To determine the effect of gas density, four gases of molecular weights from 4 to 131 were used and deionized water (coalescing) and water saturated with carbon dioxide (repressed coalescence) were used as the liquids. Very low gassing rates with impeller speeds just above the flooding-loading transition were used to allow an unobstructed light path for photography of a flat-bottomed vessel of 0.61 m diameter.
All the bubble size distributions show positive skewness with most bubbles less than 0.2 mm in diameter. The Sauter mean is in the range of 0.35 to 0.7 mm. These sizes are smaller than have usually been reported because of the point of measurement. The Sauter mean diameters decrease with increasing impeller speed, but not as rapidly as implied by Kolmogoroffs theory of isotropic turbulence. The size also increases slightly with increasing gassing rate or molecular weight of gas.