Thermodynamics Mech3001 - Week 11 - Problem 1 (11.17)

11.17 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 compressor is 60 kPa and -34°C and the compressor is estimated to gain a net heat of 450 W from surroundings. Show the cycle on a T – s diagram. Determine:

a) The quality of the refrigerant at the evaporator inlet (Answer: 0.4796)
b) the refrigeration load (Answer: 5.404 kW)
c) the COP of the refrigerator (Answer: 2.15)
d) Theoretical maximum refrigeration load for the same power input to the compressor. (Answer: 12.72 kW)

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1.b An air conditioner with refrigerant-134a as the working fluid is used to keep a room at 26°C by rejecting
the waste heat to the outside air at 34°C. The room is gaining heat through the walls and the windows at
a rate of 250 kJ/min while the heat generated by the computer, TV, and lights amounts to 900 W. An
unknown amount of heat is also generated by the people in the room. The condenser and evaporator
pressures are 1200 and 500 kPa, respectively. The refrigerant is saturated liquid at the condenser exit and
saturated vapor at the compressor inlet. If the refrigerant enters the compressor at a rate of 100 L/min and
the isentropic efficiency of the compressor is 75 percent, determine (a) the temperature of the refrigerant
at the compressor exit, (b) the rate of heat generation by the people in the room, (c) the relative COP of
[10 Marks]
the air conditioner.
pintoined at 15°C, and it requires refrigeration at a rate of 100 kW.
on