Four impellers, including a 3-blade

Four impellers, including a 3-blade propeller (PR30, supplier: Heidolph), a 6-alternating pitched (45°) blade turbine (A-45PBT6), a 6-blade disc turbine (DT6) and a disc impeller (DI), were chosen in the experiments. The blades of A-45PBT6 arranged in such a way that they alternatively pump upward and downward, potentially introduce more chaotic flow and eventually minimize the IMRs. Photographs of the impellers used in this study are shown in Fig. 2. All impellers have identical diameter of 70 mm (i.e. diameter to tank ratio of 0.36), except that DI (without the blades) has diameter of 50 mm (D/T = 0.26). The detailed specifications of all impellers are shown in Table 1. It should be pointed out that the diameter of DI is smaller than the other impellers, but it is still reasonably hypothesized that even if the diameter of the DI is equivalent to the other impellers, the bladeless geometry will probably still be the least efficient of the four impellers.