Thermodynamics

This problem could be eliminated by using a working fluid with a verysteep saturated vapor line.3. The isentropic compression process (process 4-1) involves the compressionof a liquid–vapor mixture to a saturated liquid. There are two difficultiesassociated with this process. First, it is not easy to control the condensationprocess so precisely as to end up with the desired quality at state 4. Second, itis not practical to design a compressor that handles two phases.Some of these problems could be eliminated by executing the Carnotcycle in a different way, as shown in Fig. 10–1b. This cycle, however, presentsother problems such as isentropic compression to extremely high pressuresand isothermal heat transfer at variable pressures. Thus we concludethat the Carnot cycle cannot be approximated in actual devices and is not arealistic model for vapor power cycles.10–2 ■ RANKINE CYCLE: THE IDEAL CYCLEFOR VAPOR POWER CYCLESMany of the impracticalities associated with the Carnot cycle can be eliminatedby superheating the steam in the boiler and condensing it completelyin the condenser, as shown schematically on a T-s diagram in Fig. 10–2. Thecycle that results is the Rankine cycle, which is the ideal cycle for vaporpower plants. The ideal Rankine cycle does not involve any internal irreversibilitiesand consists of the following four processes:1-2 Isentropic compression in a pump2-3 Constant pressure heat addition in a boiler3-4 Isentropic expansion in a turbine4-1 Constant pressure heat rejection in a condenserChapter 10 | 553INTERACTIVETUTORIALSEE TUTORIAL CH. 10, SEC. 1 ON THE DVD.w pump,in2PumpBoiler3Turbine4w turb,outTq in3w turb,out1q inq outsCondenser241q outw pump,inFIGURE 10–2The simple ideal Rankine cycle.