Flow-number

The values of the discharge flow number and of the circulation flow number calculated for the different working conditions are gathered in Table 4.12, together with fluid density and angular velocity. Discharge and circulation flow are calculated from flow field data as described in Appendix A.

Table 4.12: Discharge and circulation flow for simulations made for BE12500.

$Re$	Discharge flow	Circulation flow	Density	RPM
60	312.	311.	1000	50
1200	487.6	568.8	1000	50
12000	907.9	1134.3	1000	50
1200000	813.6	1058.7	1000	50

It can be observed that discharge and circulation flow are equal for simulation S1, while the difference between the flows increases with the Reynolds number. A larger amount of fluid is entrained by the jets discharged from the blades when the Reynolds is larger, i.e. when the discharged jets are more energetic or jets are released in a low viscosity fluid. Figure 4.38 shows values of discharge flow number and of circulation flow number plotted against Reynolds number. The trend for the discharge flow number is rather different from that of CE12500. Comparison between the discharge flow number for the retreated curved blade impeller and the turbofoil turbine is shown in Figure 4.39. The pumping ability of the turbofoil turbine is larger than for the retreated curved blades impeller in the high Reynolds range, and lower in the low Reynolds range. Since CE12500 and BE12500 are the same vessel equipped with two different agitators, this direct comparison is particularly informative.

Figure 4.38: Discharge Flow number and Circulation Flow number versus Reynolds number: BE12500.

Figure 4.39: Comparison of discharge flow number for retreated curved blade impeller and turbofoil turbine.

Power number values and corresponding discharge flow number are also used to calculate the pumping efficiency of the turbofoil turbine in the different operative conditions. Figure 4.40 shows variation of pumping efficiency as a function of Reynolds number. For the BE12500 pumping efficiency stabilizes around a value of 0.6 for Reynolds number larger than $10^4$. Comparison with Figure 4.27 obtained for the CE12500 reactor shows that pumping efficiency is larger for the turbofoil turbine in the high Reynolds range. Comparison between pumping efficiency for the retreated curved blade impeller and the turbofoil turbine is shown in Figure 4.41. The larger power consumption of the turbofoil turbine is well balanced by the enhanced pumping capability in the high Reynolds range. In these conditions, the turbofoil efficiency is higher than for the retreated curved blade impeller. In the low Reynolds range this is not true. The larger power consumption of the turbofoil is not balanced by a better pumping capability, and the retreated curved blade impeller is more efficient.

Figure 4.40: Pumping efficiency versus Reynolds number: BE 12500.

Figure 4.41: Comparison of pumping efficiency for the retreated curved blade impeller and the turbofoil turbine.