The schematic diagram of experimental setup is shown in
Fig. 1. Experiments were carried out in a semi-batch manner The diameter of the stirred tank is 0.24 m and the total height is 0.428 m. Four baffles with width of
0.024 m are equipped equally-spaced at the wall. The liquid height for all experiments is set at H¼T. The sparger with diamete of 0.08 m and 16 holes (diameter of 0.0015 m) is
installed underneath the impeller. The off-bottom clearance of the
sparger is T/10 in most experiments; and T/4 and T/6 are just used
to test the influence of sparger locations with respect to the
impeller. Different types of stirrers are used as shown in Fig. 2,
namely, Rushton disk turbine (RDT), half circle blade disk turbine
(HCDT), 451 pitched blade turbine downflow (PBTD) and 451
pitched blade turbine upflow (PBTU). The four impellers have