Page 342 - Steam Turbines Design, Applications, and Rerating

316 Chapter Fifteen

785
V b /V j = 0.46; V j = V b /0.46 = = 1705 ft/s
.46

V j = 224 ΔH = 1705 ft/s
2
2
ΔH = (V j /224) = (1705/224) = 58.0 Btu/lb
h 1 (from Mollier chart or steam tables) = 1305.7 Btu/lb
h 2 = 1305.7 − 58.0 = 1247.7 Btu/lb
Exhaust pressure (from Mollier chart) = 230 psia

Assuming a stage efficiency of 80 percent, the stage exit conditions are:
exhaust pressure 230 psia;
h 2e = 1305.7 − (.8) (58.0) 1259.3 Btu/lb.
Example 15.3: Straight Rateau staging Conditions: 400 psig (415 psia), 600°F,
exhaust pressure 100 psig (115 psia). Find the number of 35-in diameter Rateau
stages required, at 5000 r/min, assuming optimum stage efficiency. (See Fig.
15.7.)
From Mollier chart, the isentropic heat available is:

1305.7 − 1184.2 = 121.5 Btu/lb

(a) (b)
Figure 15.7 Isentropic heat drop and end points for straight Rateau staging. (Elliott
Company, Jeannette, Pa.)