Comparison of mass transfer performance for various single and twin impellers

The mass transfer in the air-water system was investigated for various sing le- and twin-impeller systems including the standard Rushton impellers, pit ched-blade impellers, concave-blade impellers and comb-blade impellers. For twin-impeller systems, the effects of the two impellers operating at vario us speed combinations, opposite impeller rotation and alternate impeller ro tation were investigated. Results showed that although slightly better perf ormance was achieved by using the concave-blade and comb-blade impellers, a ll the volumetric mass transfer coefficients, k(L)a, obtained were mainly d etermined by the specific power consumption (P/V) and the superficial gas v elocity (U-s) and correlated reasonably well by a single correlation due to van't Riet. The possible reason for the better performance of the comb-bla de impellers is discussed.