Info

** transition to rj

= 9.38 in (238.3 mm) and At= 32.6 in* (21032 mm ) due to tongue thickness

duces smaller areas upstream of the throat than does the former. Frictional effects in the smaller-A„ portion of the volute are less prominent using the linear approach. A CFD assessment at all flow rates can be made to guide the design choice here. Finally, the one-dimensional constant rvVv method can be improved upon by integrating a constant rVs distribution over each cross section, and the proper design must satisfy also continuity26.

Estimated Performance Characteristics Detailed computation of hydraulic losses, together with leakage, disk friction, and other mechanical drags was done as described previously, and the results are presented in Figure 30. The method predicts the pump efficiency to be 85.5% at the design point of 2500 gpm (0.1577 m3/s), peaking at 86 percent at a 5% lower flow rate. The power consumption peaks at the design point at 77 hp (57 kW), indicating that this is a "non-overloading" design; that is, shaft power does not increase beyond this flow rate. The empirical methods reviewed earlier for shut-off head and power were applied here and blended into the one-dimensionally computed curves at half of the BEP flow rate.

The shut-off head coefficient value of 0.596 is close to the 0.585 value of Stepanoff4 and is admittedly open to alteration. The rise of head from design point to shut-off is from 104 up to 161 ft (31.7 up to 49.1 m) or 55%. This percentage could be smaller and still ensure stable operation in any typical system; however, the non-overloading feature could change, the power peaking at a higher flow rate. In retrospect, the design-point head coefficient C of 0.385 could be larger without the diffusion-factor results of Figure 29 becoming excessive. One would conclude from this exercise that the C-curve of Figure 12 is conservative and could be higher. Of more significance, however, is the demonstration in this design example of the utilization of easily applied fundamental fluid dynamical analyses such as the diffusion assessment illustrated in Figure 29 as the basic arbiters of design choices such as the head coefficient, number of blades, and so on. Furthermore, the shapes of the performance characteristics are revealed.

Shaft 40 power,

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