Thermodynamics

w pump,in213 MPa75 kPaPumpBoilerFIGURE 10–3Schematic and T-s diagram for Example 10–1.q inIt is also interesting to note the thermal efficiency of a Carnot cycle operatingbetween the same temperature limitsh th,Carnot 1 T minT max 1 The difference between the two efficiencies is due to the large external irreversibilityin Rankine cycle caused by the large temperature differencebetween steam and combustion gases in the furnace.3 MPa350°C3w turb,outTurbine75 kPa 4q outCondenser75 kPa191.76 2732 K1350 2732 K 0.415 Chapter 1034s 3 = s 4| 557T, °C35021s 1 = s 2 s3 MPa75 kPa10–3 ■ DEVIATION OF ACTUAL VAPOR POWERCYCLES FROM IDEALIZED ONESThe actual vapor power cycle differs from the ideal Rankine cycle, as illustratedin Fig. 10–4a, as a result of irreversibilities in various components.Fluid friction and heat loss to the surroundings are the two common sourcesof irreversibilities.Fluid friction causes pressure drops in the boiler, the condenser, and thepiping between various components. As a result, steam leaves the boiler at asomewhat lower pressure. Also, the pressure at the turbine inlet is somewhatlower than that at the boiler exit due to the pressure drop in the connectingpipes. The pressure drop in the condenser is usually very small. To compensatefor these pressure drops, the water must be pumped to a sufficientlyhigher pressure than the ideal cycle calls for. This requires a larger pumpand larger work input to the pump.The other major source of irreversibility is the heat loss from the steam tothe surroundings as the steam flows through various components. To maintainthe same level of net work output, more heat needs to be transferred toINTERACTIVETUTORIALSEE TUTORIAL CH. 10, SEC. 2 ON THE DVD.