EFFECT OF BLADE PITCH ON THE STRUCTURE OF THE TRAILING VORTEX AROUND RUSHTON TURBINE IMPELLERS

Effect of blade number on the structure of the trailing vortex around the Rushton turbine impeller is examined by analyzing the data of mean velocities, deformation rates, turbulent kinetic energy and energy di ssipation rates for 2-, 4-, 6- and 8-straight blades disk turbine impe llers in a baffled standard geometry stirred tank. The data of Sauter mean bubble diameter near the blade tip are combined with the turbulen t characteristics around the vortex to discuss how the blade number an d the strength of the vortex affect the performance of the gas dispers ion around the Rushton turbines under a low gassing rate. The results of this analysis show that if power input per each blade is the same, the impeller having four blades not only has the strongest average mea n deformation rates and the largest turbulent kinetic energy, but also disperses the smallest average bubbles under the same gassing rate.