The effects of blade angle, blade number, tongue length, and scroll contour have been dis-cussed in the previous section are organized in Table 4. It should be noticed that the recommen-dations in Table 4 are based on cost/performance and the balance between higher static pressure rise, higher flow rate, and lower manufacturing cost. Based on the conclusions recorded in Table 4, the virtual Model A+ was modified from Model A with all favored parameter changes:
A, D, and G.
The schematic of the impeller wheel and the scroll for virtual Model A+ is shown in Figure 15. The virtual Model A+ was first constructed in CAD and then imported into GAMBIT and FLUENT. Simulations were performed to produce performance data. Comparing simulated results between Models A and A+, the performance and efficiency curves are shown in Figure 16. It can be found that the performance curve for the optimized model moves upward-right, meaning higher static pressure and volume flow rate. The peak efficiency for the optimized model decreases about 5%. However, the efficiency increases significantly in the high flow rate region. Taking an average from all operating points, the optimized design exhibits a 7.9% improvement in static pressure and a 1.5% improvement in efficiency. The results show that the optimization is successful. The conclusive favored parameter changes are a valuable ref-erence for future blower designs.
CONCLUSION
In this study, backward-curved airfoil centrifugal blowers were numerically simulated and analyzed. The results from numerical simulations and measurements were compared to verify the validity of numerical simulation.
The numerical simulations of centrifugal blowers are shown to be effective. The deviations of the performance curves and the efficiency curves are within 4.8% and 15.1%, respectively. The effects of blade angle, blade number, tongue length, and scroll contour were numerically stud-ied. Some favored parameter changes were determined and utilized to redesign one of the
Figure 15. Schematic of the blower with the optimized parameters (virtual Model A+).
Figure 16a. Performance comparison between Model A and virtual Model A+ (SI units).
Figure 16b. Performance comparison between Model A and virtual Model A+ (I-P units).
blowers. The optimized model indeed exhibits a better value of cost/performance. This further shows that the presented simulation scheme is successful and that the favored parameter changes are a good reference for future blower designs.
ACKNOWLEDGMENT
The authors gratefully acknowledge the support from National Science Council (NSC) of Tai-wan (Grant number NSC 94-2622-E-027-045-CC3).
NOMENCLATURE
bhp = brake horsepower, W (Btu/h) g = acceleration of gravity, m/s2 (ft/s2) H = net head, m (ft)
= mass flow rate, kg/s (lb/s) Q = volume flow rate, m3/s (ft3/m) r = radius, m (ft)
T = torque, N⋅m (ft⋅lbf) U = tangential speed, m/s (ft/s) V = velocity, m/s (ft/s) w = impeller wheel width, m(ft) W = work, J (Btu)
1 = inner periphery of impeller wheel 2 = outer periphery of impeller wheel
t = tangential component n = normal component
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