Bubble Size Distribution in a Gas Sparged Vessel Agitated by a Rushton Turbine

The effect of agitation, due to a Rushton turbine, on the bubble size and bubble size distribution has been studied in an aerated vessel. By using a noncoalescing system, it has been possible to study the bubble breakup process in isolation. Bubbles of two different sizes, with d[sub 32] of 300 [mu]m and 2.5 mm, are generated using porous spargers. With no agitation, the bubble populations are found to exhibit a log-normal distribution. The 300-[mu]m bubbles are too small to undergo further breakage for the range of impeller speeds studied, and the size distribution is preserved. The larger bubbles are broken by agitation and the d[sub 32] decreases. Also with increasing agitation, the size distribution changes from unimodal to bimodal, and again to unimodal, as the bubble population moves progressively down the size scale. A model proposed, based on the energy dissipated in the impeller zone, predicts the continually changing pattern of the bubble size distributions satisfactorily.