The influence of Rushton impeller blade and disk thickness on the mixing characteristics of stirred vessels

The influence of impeller blade and disk thickness on the mixing characteristics of stirred vessels operating with a single Rushton impeller have been investigated. Laser Doppler anemometry (LDA) measurements of the mean and fluctuating velocities, ensemble-averaged over both 360 degrees of impeller revolution and between a specific impeller blade pair (over 60 degrees), were performed in vessels of diameter (T) 100 mm and 294 mm in order to characterize the flow in the impeller vicinity and to assess the effect of vessel scale. The velocity profiles are presented and how numbers (Fl) are calculated, which show Fl to decrease by up to 15% as the ratio of impeller blade and disk thickness (t) to diameter (D), was increased from 0.008 to 0.033. Torque measurements performed using a telemetric strain gauge arrangement showed a reduction in impeller power number (Po) by up to 33%, with a similar increase in impeller thickness ratio, while the mixing time (t(M)) increased by around 15% with increasing t/D. The effects of t/D on the mean and fluctuating velocity components in the two vessels are also reported and the influence of vessel scale on the flow characteristics is assessed.