Thermodynamics

Chapter 10 | 559EXAMPLE 10–2 An Actual Steam Power CycleA steam power plant operates on the cycle shown in Fig. 10–5. If the isentropicefficiency of the turbine is 87 percent and the isentropic efficiency ofthe pump is 85 percent, determine (a) the thermal efficiency of the cycleand (b) the net power output of the plant for a mass flow rate of 15 kg/s.Solution A steam power cycle with specified turbine and pump efficienciesis considered. The thermal efficiency and the net power output are to bedetermined.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. 10–5. The temperatures and pressures of steam at variouspoints are also indicated on the figure. We note that the power plant involvessteady-flow components and operates on the Rankine cycle, but the imperfectionsat various components are accounted for.(a) The thermal efficiency of a cycle is the ratio of the net work output to theheat input, and it is determined as follows:Pump work input:w pump,in w s,pump,in v 1 1P 2 P 1 2h p h p 10.001009 m3 >kg23116,000 92 kPa40.85 19.0 kJ>kg1 kJa1 kPa # b m315.9 MPa35°C 15.2 MPa3625°CBoiler415 MPa52 16 MPa600°Cw turb,outT4w pump,inTurbineη T = 0.875Pumpη P = 0.85610 kPa19 kPa38°CCondenser322s16s 6sFIGURE 10–5Schematic and T-s diagram for Example 10–2.