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ME212PS2 - ME 212 PS II 19.03.2008 1 A commercial...

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ME 212 PS II 19.03.2008 1) A commercial refrigerator with refrigerant- 134a as the working fluid is used to keep the refrigerated space at 30°C by rejecting its waste heat to cooling water that enters the condenser at 18°C at a rate of 0.25 kg/s and leaves at 26°C. The refrigerant enters the condenser at 1.2 MPa and 65°C and leaves at 42°C. The inlet state of the compressor is 60 kPa and -34°C and the compressor is estimated to gain a net heat of 450 W from the surroundings. Determine ( a ) the quality of the refrigerant at the evaporator inlet, ( b ) the refrigeration load, ( c ) the COP of the refrigerator, and ( d ) the theoretical maximum refrigeration load for the same power inputto the compressor. 2) Consider a two-stage cascade refrigeration system operating between the pressure limits of 1.2 MPa and 200 kPa with refrigerant-134a as the working fluid. The refrigerant leaves the condenser as a saturated liquid and is throttled to a flash chamber operating at 0.45 MPa. Part of the refrigerant evaporates during this flashing process,

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ME212PS2 - ME 212 PS II 19.03.2008 1 A commercial...

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