Superheated steam enters an adiabatic turbine at 10 MPa and 500 °C, and exits at 4.5 MPa and 400 °C. The isentropic efficiency is closest to:Question 8Select one:a.77%b.80%c.71%d.74%
Question
Superheated steam enters an adiabatic turbine at 10 MPa and 500 °C, and exits at 4.5 MPa and 400 °C. The isentropic efficiency is closest to:Question 8Select one:a.77%b.80%c.71%d.74%
Solution
To solve this problem, we need to use the definition of isentropic efficiency for a turbine, which is given by:
η = (h1 - h2) / (h1 - h2s)
where:
- h1 is the enthalpy of the steam entering the turbine,
- h2 is the enthalpy of the steam exiting the turbine, and
- h2s is the enthalpy of the steam exiting the turbine in an isentropic process.
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First, we need to find the enthalpies h1, h2, and h2s. We can find these values from the steam tables using the given pressures and temperatures.
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For the initial state (10 MPa and 500 °C), we find h1 from the superheated steam table.
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For the final state (4.5 MPa and 400 °C), we find h2 from the superheated steam table.
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To find h2s, we need to assume an isentropic process from the initial state to the final state. This means that the entropy remains constant. So, we find the entropy at the initial state from the steam table, and then find the enthalpy at the final state that corresponds to this entropy. This is h2s.
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Once we have the values of h1, h2, and h2s, we can substitute them into the formula for isentropic efficiency and solve for η.
Please note that without the actual steam tables or the exact enthalpy values, I can't provide a numerical answer. But this is the process you would follow to solve this problem.
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