Q6. The vapor compression refrigeration plant show in Fig.Q6 uses R134a as the working fluid. The evaporator cools dry air entering a compartment containing electrical equipment, the air leaving the compartment is used to cool the condenser.
At a particular operating condition.
The pressure and temperature at the compressor section are 2.4335 bar and 5℃ respectively.
The compressor discharge pressure and temperature are 6.6525 bar and 45℃ respectively. The liquid refrigerant enters the expansion valve at a temperature of 25℃.
Dry air enters the evaporator at a temperature of 15℃ and leaves at a temperature of -2.79℃.
The air gains 4 kW of heat energy as it passes through the compartment.
The compressor has a swept volume of 4.6457 x 10-3 m3 and a volumetric efficiency of 0.95 at a speed of 270 rev/min.
(a) Calculate EACH of the following:
(i) The compressor power; (4)
(ii) The volume of air flowing through the system; (4)
(iii) The temperature of the air leaving the condenser coils. (4)
(b) Sketch the cycle on a Pressure-specific enthalpy diagram showing.
(i) The cardinal points and vapour dome; (1)
(ii) Irreversible processes as dashed lines; (1)
(iii) The regions of work and heat transfer. (2)
Note: For R134a at 2.4335 bar and 5℃ specific volume v = 0.0993 m3/kg
For air Cp = 1.004 kJ/kg K, ρ = 1.263 kg/m3.
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