An air-conditioner with refrigerant-134a as theworking fluid is used to keep a room at 23°C by rejectingthe waste heat to the outdoor air at 34°C. The roomgains heat through the walls and the windows at a rate of250 kJ/min while the heatgenerated by the computer, TV, and lights amounts to 900 W. The refrigerant enters the compressorat 400 kPa as a saturated vapor at a rate of 80 L/minand leaves at 1200 kPa and 70°C. Determine (a) the actualCOP, (b) the maximum COP, and (c) the minimumvolumeflow rate of the refrigerant at thecompressor inlet for thesame compressor inlet and exit conditions.

a) COPactual=4.33

b) COPmaximum=26.91

c) vminimum=0.00021 m^3/s

Explanation:

The properties of saturated refrigerant R-134a can be obtained from tables at 400 kPa

h1=enthalpy=255.61 kJ/kg

v1=specific volume=0.05127 m^3/kg

The properties of superheated refrigerant R-134a can be obtained from tables at 1.2 MPa and 70°C

h2=300.61 kJ/kg

a) the mass flow rate is:

where v11 is the volume flow rate at inlet 1= 80 L/min=0.00133 m^3/s. Replacing values:

The power consumption of the compressor is:

The refrigeration load is:

Qheat=250 kJ/min=4.17 kJ/s

The coefficient of performance is:

b) The maximum coefficient of performance of a reversible refrigerator is:

TL=23°C=296 K

TH=34°C=307 K

Replacing:

c) The minimum power input to the condenser is:

The minimum mass flow rate is:

The minimum volume flow rate is:

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