Figure 12. 3D contour plots of the dimensionless mean axial velocity (a)
and absolute radial velocity (b) at different axial positions.
Effective mass exchange in the axial and radial directions can be
further evaluated by the flow rates, which are calculated from the axial
flow rates by integrating the radial profiles of the time-averaged mean
axial velocity. Detailed information could be found in our previous work19. In this work, the
time-averaged axial flow rate per unit area cross the horizontal as a
function of z /T and time-averaged radial flow rate per
unit area as a function of r /R are calculated and plotted
in Figure 13, respectively. It is seen that there are two humps atz /T = 0.2 and z /T = 1.1 on the curves of the
axial flow rates, where the lower short blades and upper short blades
are located, respectively. In addition, the axial flow rate decreases
gradually from the maximum value at z /T = 0.2 to a minimum
value at z /T = 0.6, where the connected blades are
located. This provides a further proof that part of the up-flow is
gradually discharged to the radial flow along the axial direction.
Similar trends are found when z /T decreases from 1.1 to
0.6, corresponding to the gradually discharging of the down-flow to the
radial flow from the top. The profiles of the flow rate per unit areavs. r /R , as shown in Figure 13b, have obvious
maximum values at r /R = 0.4-0.5 where the up-flow and
down-flow meet with intensive interaction, implying that effective axial
mass exchange between the upper and lower parts of the tank can be
achieved.