chapter 6 examples heat transfer, Exercises of Heat and Mass Transfer

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6-23 Anautomobile engine consumes fuel at a rate of 22 L/h and delivers 55 kW of power to the wheels. If the fuel has a heating value of 44,000 kJ/kg and a density of 0.8 g/cm’, deter- mine the efficiency of thisengine. Answer: 25.6 percent 6-23 The power outputand fuel consumption rate of acar engine are given. Thethermal efficiency of the engine is to be determined. Assumptions The car operates steadily. Properties The heating value of the fuelis given tobe 44,000 ki/kg. Analysis The mass consumption rate of the fuel is tet = (MV ees = (0.8 kg/L)(22 L/h) = 17.6 kg/h ‘The rate of heat supply to the caris 2p, = Poa MV cat = (17.6 kg/h)(44,000 ki/kg) = 774,400 ki/h = 215.1 kW ‘Then the thermal efficiency of the carbecomes Wronoa _ _SSKW = = = 0.256 = 25.6% eG) DISTkW