Thermodynamics

614 | Thermodynamicsand the turbine would produce 0.33 kW of power. This would decrease thepower input to the refrigerator from 1.81 to 1.48 kW and increase the rate ofheat removal from the refrigerated space from 7.18 to 7.51 kW. As a result,the COP of the refrigerator would increase from 3.97 to 5.07, an increase of28 percent.INTERACTIVETUTORIALSEE TUTORIAL CH. 11, SEC. 3 ON THE DVD.11–4 ■ ACTUAL VAPOR-COMPRESSIONREFRIGERATION CYCLEAn actual vapor-compression refrigeration cycle differs from the ideal onein several ways, owing mostly to the irreversibilities that occur in variouscomponents. Two common sources of irreversibilities are fluid friction(causes pressure drops) and heat transfer to or from the surroundings. TheT-s diagram of an actual vapor-compression refrigeration cycle is shown inFig. 11–7.In the ideal cycle, the refrigerant leaves the evaporator and enters thecompressor as saturated vapor. In practice, however, it may not be possibleto control the state of the refrigerant so precisely. Instead, it is easier todesign the system so that the refrigerant is slightly superheated at the compressorinlet. This slight overdesign ensures that the refrigerant is completelyvaporized when it enters the compressor. Also, the line connectingWARMenvironmentT4Condenser3Q H23252'6Expansionvalve Compressor1W in456 781Evaporator7 8Q LCOLD refrigeratedspacesFIGURE 11–7Schematic and T-s diagram for the actual vapor-compression refrigeration cycle.