Download Thermodynamic Cycles Knowledge Check

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Wt.actual = actual work done by the turbine (ft-lbf)
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Wt.ideal = work done by an ideal turbine (ft-lbf)
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(hin – hout)actual = actual enthalpy change of the working fluid
(BTU/lbm)
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(hin – hout)ideal = actual enthalpy change of the working fluid in an ideal
turbine (BTU/lbm)
Figure: Entropy Diagram Measures System Efficiency
A vertical line on the T-s diagram is a constant entropy ideal process.
Entropy increases in the actual turbine process. The smaller the increase in
entropy, the closer the turbine efficiency (ηt) is to 1.0 or 100 percent.
If an ideal turbine became a real turbine, its output would decrease due to
losses such as friction, windage, moisture, and tip leakage. To raise the
turbine back to its original output, the turbine steam supply valves would
open, increasing the mass flow rate of the steam going into the turbine. The
work of the turbine increases to overcome the losses. Opening the steam
supply valves decreases steam generator pressure and adding more heat
raises the steam generator pressure back to its original value. However,
since the heat added is greater than the increase in work from the turbine,
the cycle efficiency decreases.
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