A steam turbine inlet is at 1200 kPa, 500°C. The exit is at 200 kPa.

1.	A steam turbine inlet is at 1200 kPa, 500°C. The exit is at 200 kPa. What is the lowest possible exit temperature? Which efficiency does that correspond to?
Answer» We would expect the lowest possible exit temperature when the maximum amount of work is taken out. This happens in a reversible process so if we assume it is adiabatic this becomes an isentropic process. Exit: 200 kPa, s = sin = 7.6758 kJ/kg K ⇒ T = 241.9°C The efficiency from measures the turbine relative to an isentropic turbine, so the efficiency will be 100%.

A steam turbine inlet is at 1200 kPa, 500°C. The exit is at 200 kPa. What is the lowest possible exit temperature? Which efficiency does that correspond to?

Answer»

We would expect the lowest possible exit temperature when the maximum amount of work is taken out. This happens in a reversible process so if we assume it is adiabatic this becomes an isentropic process.

Exit: 200 kPa, s = sin = 7.6758 kJ/kg K ⇒ T = 241.9°C

The efficiency from measures the turbine relative to an isentropic turbine, so the efficiency will be 100%.

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A steam turbine inlet is at 1200 kPa, 500°C. The exit is at 200 kPa. What is the lowest possible exit temperature? Which efficiency does that correspond to?

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