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.