FLUID AND PARTICLE MOTION IN TURBULENT STIRRED TANKS - FLUID MOTION

Using streak photography, fluid velocities were measured in baffled tanks turbulently agitated by six-bladed turbine impellers. Outside of the impeller discharge zone (in most of the tank) the average and r.m.s. fluctuating velocities were found to be proportional to the rotational speed of the impeller and its diameter squared, and inversely proportional to the cube root of the tank volume. This relationship was verified over a wide range of impeller and tank sizes, fluid properties, and agitator speeds, and agrees in form with predictions based on dimensional analysis of the power dissipation in such tanks. The similarity of the turbulent power-dissipation correlation—i.e., constancy of the power number—for a large number of impeller-tank arrangements suggests that the present fluid velocity correlation may have broad applicability, and that maintaining a constant value of ND2/(T2H)1/3 may be a suitable scale-up criterion in many instances. Further, this fluid velocity correlation helps explain various anomalies in correlations which have been proposed for heat and mass transfer in stirred tanks. © 1968, American Chemical Society. All rights reserved.