Flow patterns
The improved TKE performance calls for an analysis of the flow patterns generated by the MBC agitator. Here, CFD predictions for the case ofN = 90 rpm are adopted. Firstly, the time-averaged mean velocity vectors on the r -z planes of P-10, P45, and P10 are plotted in Figure 11. To understand fully the magnitude of the total velocity, the contour plots are colored by the dimensionless velocity magnitude,U /U tip. It is found that the maximum velocities of about 0.9Utip occur near the upper and lower short blades. In the upper region, fluid discharge by the upper short blades produce two big vortexes and a strong axial down-flow in the center. In the axial direction down, part of the down-flow is discharged in the radial direction, which should be attributed to the long blades. The rest of the down-flow continues going down. Different from the flow patterns in the upper part of the vessel, two big vortexes are formed near the lower short blades and a strong axial up-flow in the center is generated. Similarly, part of the up-flow is discharged in the radial direction by the long blades and the rest goes up. The down-flow and the up-flow meet near the middle connected blades, producing a strong radial flow in combination with the discharge by the connected blades. It is noted that the radial flow along the whole long blade is beneficial for the mass exchange in the radial direction. In addition, different from the traditional RT impeller, strong impingement of the down-flow in the upper region and up-flow in the lower region results in effective mass exchange in the axial direction, due to the absence of the disk.