Optimal Impeller Clearance for a Dual Stirred Unbaffled Tank with a Concave Blade Impeller

An experimental investigation of unbaffled stirred tanks is carried out with the use of a dual concave blade impeller to evaluate the mass transfer coefficient, power number, and vortex depth. The effect of the impeller clearance on mass transfer is analyzed to estimate the optimal impeller clearance for lower and upper impellers. It is found that the lower impeller positioned at 0.25 of the tank diameter with the clearance between the lower and upper impellers equal to 0.38 of the tank diameter gives the maximum mass transfer coefficient. A comparison with the results for dual Rushton and Rushton-concave impellers at the optimal clearance shows that the concave-concave impellers are most efficient. The scale-up criteria for optimal, geometrically similar systems of unbaffled stirred tanks with a dual concave impeller are proposed. © 2016, Springer Science+Business Media New York.