Page 341 - Steam Turbines Design, Applications, and Rerating

Elliott Shortcut Selection Method for Steam Turbines 315

568
V b
V b /V j = 0.23; V j = = = 2470 ft/s
.23 .23

V j = 224 ΔH = 2470 ft/s
ΔH = 121.5 Btu/lb

h 1 (from Mollier chart or steam table) = 1459.9 Btu/lb
h 2 = 1459.9 − 121.5 = 1338.4 Btu/lb
Exhaust pressure (from Mollier chart) = 590 psia
Assuming a stage efficiency of 70 percent, the stage exit conditions are:
exhaust pressure 590 psia
h 2e = 1459.9 − (.7) (121.5) 1374.8 Btu/lb.
Example 15.2: Rateau stage performance Conditions: 400 psig (415 psia),
600°F, 5000 r/min, 35-in wheel diameter. Assume 1-in blade height. Find isen-
tropic heat drop and end point. (See Fig. 15.6.)
πDN (3.14)(35 + 1)(5000)
V b = = = 785 ft/s
720 720
From Fig. 15.4, velocity ratio for optimum Rateau stage efficiency = 0.46

(a) (b)
Figure 15.6 Isentropic heat drop and end points for a Rateau stage. (Elliott Com-
pany, Jeannette, Pa.)