Effect of Impeller Blade Number on KLa in Mechanically Agitated Vessels
Journal
Korean Journal of Chemical Engineering
Journal Volume
16
Journal Issue
5
Pages
703-708
Date Issued
1999
Author(s)
Abstract
Effects of impeller blade number on gas dispersion and mass transfer rate were thoroughly investigated for mechanically agitated vessels equipped with 2-, 4-, 6- and 8-straight blades disk turbine impellers. The results show that under the same rotational speed, the impeller with more blades always can disperse gas more effectively, which induces a higher value of 〈KLa〉. However, with the same total power consumption, the 4-blade impeller can obtain a higher 〈KLa〉 value than the 6- and 8-blade impellers under a lower gassing rate condition (Qg<0.5 vvm), but if Qg exceeds 0.5 vvm, the 6-blade impeller will perform better than the 4- and 8-blade impellers. To examine the results obtained from the single impeller systems, the same approach is applied to measure 〈KLa〉 values for the triple stage 6-blade impeller system (3×6) and quadruple stage 4-blade impeller system (4×4). From the experimental results, it can be found that the 4×4 system gives higher 〈KLa〉 value than the 3×6 system under gas completely dispersed conditions. By correlating 〈KLa〉 with nb, N and Vs, the following correlation can be given as: 〈KLa〉 =0.00119nb0.62N1.56Vs0.4 or 〈KLa〉 =0.0297nb0.1(Pg/V)0.34V s0.48 These two correlations can also be used to evaluate the mass transfer coefficient of each impeller region for the multiple impeller systems and the deviation is always less than 10%.
Type
journal article