A steam turbine inlet is at 200 psia, 800 F. The exit is at 40 psia, 600 F. What is the isentropic efficiency?
Question 7.227E: A steam turbine inlet is at 200 psia, 800 F. The exit is at ...
from table F.7.2
Inlet: h _{ in }=1425.31 Btu / lbm , s _{ in }=1.7659 Btu / lbm R
Exit: h _{ ex }=1333.43 Btu / lbm , s _{ ex }=1.8621 Btu / lbm R
Ideal Exit: 40 psia , s = s _{ in }=1.7659 Btu / lbm R \Rightarrow h _{ s }=1241.05 Btu / lbm
w _{ ac }= h _{ in }- h _{ ex }=1425.31-1333.43=91.88 Btu / lbm
w _{ s }= h _{ in }- h _{ s }=1425.31-1241.05=184.3 Btu / lbm
\eta=\frac{w_{a c}}{w_{s}}=\frac{91.88}{184.3}=0.498
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