Efficacy of a spinning disc as a bubble break-up device

Turbulence parameters including mean velocities, turbulent velocities, turbulent energy dissipation rates and one-dimensional turbulent energy spectra were determined in a tank of standard geometry, agitated by a Rushton turbine and a novel high-speed spinning disc-an impeller which has achieved success in the field of mineral flotation. Turbulence parameters were determined both in the unaerated tank and in the tank aerated with bubbles of various initial sizes. The relative performance of the Rushton turbine and spinning-disc impellers are compared both with respect to the generation of the above turbulent parameters and the resultant variation of these parameters with aeration. The relative bubble break up performance of the two impellers are compared in terms of measured local rates of energy dissipation and turbulent kinetic energy in the impeller zone. The results indicate that, though in the present study the spinning-disc impeller is found to be a less efficient device for bubble break up than a standard Rushton turbine, this could be rectified through a different selection of spinning-disc dimensions and operating conditions. (C) 1997 Elsevier Science Ltd.