Repeat Problem 9.58 for a turbine having an isentropic efficiency of 90% and a pump having an isentropic efficiency of 85%.

Problem 9.58

A regenerative Rankine cycle operates with a first-stage turbine inlet state of 800° C and 5MPa and a second-stage exhaust pressure of 0.01 MPa. A single open feedwater heater, as shown in Fig. 9.17, is used with an extraction pressure of 0.7MPa. Assume the exit states of condenser and of the feedwater heater are both saturated liquid. The turbine and pump efficiencies are 100%. Determine the first-law thermal efficiency for the cycle and the total turbine work rate per unit boiler mass flow rate (kJ/kg).

 Fig. 9.17

m Boiler Morn m ym Pump 2 m Open feed- water heater (a) (1-y) m 3 6 Pump 1 Turbine (1-y) m Condenser Temperature, T 21 6 m y m (1-y) m Entropy, s (b) 5 3 m 4 (1-y) m S