Gas–liquid mass transfer coefficient in stirred tanks interpreted through models of idealized eddy structure of turbulence in the bubble vicinity

Abstract

Experimental data on the average mass transfer liquid film coefficient ( k L) in an aerated tank stirred by two Rushton turbines on common shaft are presented. Liquid media used were distilled water and 0.5 M sodium sulphate solution. Volumetric mass transfer coefficient ( k L a) was measured by the dynamic pressure method with pure oxygen absorption. Specific interfacial area a was taken from Alves et al. [Chem. Eng. Proc., in press] who measured data on local gas hold-up and local average bubble diameter in the same apparatus and batches. Values of k L are quantitatively interpreted in terms of correlations based on idealized eddy structures of turbulence in the bubble vicinity, namely by “eddy” model by Lamont and Scott [AIChE J. 16 (1970) 513] in the form of k L=0.523( eν/ ρ) 0.25( D/ ν) 1/2, which fits the data with the mean deviation of 4.7%. It is shown that the decisive quantity to correlate k L in the stirred tank is power dissipated in the liquid phase rather than the bubble diameter and the slip velocity as assumed by Alves et al.