Thermodynamics

572 | ThermodynamicsSome steam leaves the turbine at a pressure of 1.2 MPa and enters the openfeedwater heater. Determine the fraction of steam extracted from the turbineand the thermal efficiency of the cycle.Solution A steam power plant operates on the ideal regenerative Rankinecycle with one open feedwater heater. The fraction of steam extracted fromthe turbine and the thermal efficiency are to be determined.Assumptions 1 Steady operating conditions exist. 2 Kinetic and potentialenergy changes are negligible.Analysis The schematic of the power plant and the T-s diagram of the cycleare shown in Fig. 10–18. We note that the power plant operates on the idealregenerative Rankine cycle. Therefore, the pumps and the turbines are isentropic;there are no pressure drops in the boiler, condenser, and feedwaterheater; and steam leaves the condenser and the feedwater heater as saturatedliquid. First, we determine the enthalpies at various states:State 1:P 1 10 kPaf h 1 h f @ 10 kPa 191.81 kJ>kgSat. liquid v 1 v f @ 10 kPa 0.00101 m 3 >kgState 2:P 2 1.2 MPas 2 s 1w pump I,in v 1 1P 2 P 1 2 10.00101 m 3 1 kJ>kg2311200 102 kPa4a1 kPa # b m3 1.20 kJ>kgh 2 h 1 w pump I,in 1191.81 1.202 kJ>kg 193.01 kJ>kgT515 MPa600°Cw turb,out5q inBoilerOpenFWHTurbine1.2 MPa 6710 kPa2436415 MPa3Pump II1.2 MPa1.2 MPa2Pump I110 kPaq outCondenser17sFIGURE 10–18Schematic and T-s diagram for Example 10–5.