GATE 2016 ME (ME1) – Question 57
An ideal Rankine-cycle plant receives superheated steam at 3 MPa, 350°C; condenser pressure is 75 kPa. The thermal efficiency is ______ %. Data at 75 kPa: hf = 384.39 kJ/kg, vf = 0.001037 m³/kg, sf = 1.213 kJ/kg K, hfg = 2278.6 kJ/kg, sfg = 6.2434 kJ/kg K. At 3 MPa, 350°C: h = 3115.3 kJ/kg, s = 6.7428 kJ/kg K.
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Correct answer: 25.8 to 26.1
Explanation
Isentropic turbine expansion gives exit quality x=(6.7428−1.213)/6.2434≈0.8857. Exit enthalpy is384.39+x·2278.6; pump work is0.001037(3000−75)=3.0332kJ/kg. Heat input is3115.3−384.39−3.0332. Divide turbine work minus pump work by this heat input to get **26.017%**.