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Unformatted text preview: Chapter 11 11-12 An ideal vapor-compression refrigeration cycle with refrigerant-134a as the working fluid is considered. The COP and the power requirement are to be determined. Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible. Analysis In an ideal vapor-compression refrigeration cycle, the compression process is isentropic, the refrigerant enters the compressor as a saturated vapor at the evaporator pressure, and leaves the condenser as saturated liquid at the condenser pressure. From the refrigerant tables (Tables A-11, A- 12, and A-13), ) throttling ( kJ/kg 32 . 107 kJ/kg 32 . 107 liquid sat. MPa 1 kJ/kg 29 . 275 MPa 1 K kJ/kg 92927 . kJ/kg 77 . 252 vapor sat. C 4 3 4 MPa 1 @ 3 3 2 1 2 2 C 4 @ 1 C 4 @ 1 1 h h h h P h s s P s s h h T f g g The mass flow rate of the refrigerant is kg/s 750 . 2 kJ/kg 107.32) (252.77 kJ/s 400 ) ( 4 1 4 1 h h Q m h h m Q L L The power requirement is kW 61.93 kJ/kg 252.77) 29 kg/s)(275. 750 . 2 ( ) ( 1 2 in h h m W The COP of the refrigerator is determined from its definition, 6.46 kW 61.93 kW 400 COP in R W Q L 11-19 A refrigerator with refrigerant-134a as the working fluid is considered. The rate of heat removal from the refrigerated space, the power input to the compressor, the isentropic efficiency of...
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- Summer '07