Abstract
The local bubble size distribution in gassed stirred tanks was investigated experimentally by using phase Doppler anemometry (PDA) and simulated numerically. From the measurements, the mean bubble velocity and the mean diameter d32 according to Sauter were calculated. The flow fields produced by impellers have a considerable impact on the distribution of the mean diameter. Large bubble sizes were detected in the ring vortices present in the large-scale flow fields, with a significant increase occurring in the lower ring vortex produced by the Rushton turbine. For the realistic treatment of bubble motion, the numerical code was implemented with the introduction of bubble break-up model. The model used is stochastic, based on the assumption that shear in the flow induces the breaking of the bubble. As a dominant parameter the dissipation of the turbulent kinetic energy was used. Results of the computed bubble velocity field agree very well with the measurements. The calculated and measured values of the mean bubble diameter are of the same order, there is a deviation of about 20 % in the local diameter distribution. The data obtained contribute to a better understanding of gas-liquid flows in stirred reactors.