Figure 14. The predicted torques acting on the shaft and on the vessel.
(a) N = 90 rpm; (b) N = 120 rpm.
As the momentum transfer occurs between the blade and the fluid, leading
to the vortex motion, thus, the torques, like other transient simulation
variables, oscillate continuously with time, as shown in Figure 14. It
is seen that the amplitude of the torque oscillation acting on the
vessel is slightly larger than that on the shaft. The power consumption
is then calculated by taking the average values of the torque.
The measured and predicted power consumption and the corresponding power
number, NP , is listed in Table 3. Here, two cases
of N = 90 rpm and N = 120 rpm are considered. We can see
that only a slight difference (less than 0.5%) exists between the
calculated NP values by the torques acting on the
shaft and on the wall. In addition, the CFD predictions demonstrate
satisfactory agreement with the experimental results, with a mean error
of 2.30%. It is noted that the experimental Nprises by 11.99 to 12.94 when N increases from 90 rpm to 120 rpm,
although the flow is in a turbulent regime30. Meanwhile, the
averaged value of NP in the case ofH /T =1.5 can reach 12.5. Whereas for the Maxblend impeller,
the NP value is just around 2 in a turbulent
regime in the case of H /T =1.131. This indicates that
the proposed MBC agitator can load the energy into the fluid
effectively, which is why efficient mass exchange in both axial and
radial directions have been achieved with improved TKE performance.
Table 3.
The
predicted and experimental torques and the corresponding power number
during an averaged time period of 50s.