Q6. A vapour cornpressian cycle using R134a as the working fluid is to be as a heat pump. The working fluid enters the compressor at a pressure and temperature of 2.006 bar and 0°C respectively with a specific volume of 0.1 m3⁄kg.
It leaves the compressor at a pressure and temperature of 7.7 bar and 50℃ respectively and the condenser at a temperature of 25°C. The compressor has a swept volume of 5.556 x 104 m3 and a volumetric efficiency of 90% at a speed 300 rev/ min.
The air cooling the condenser has flow rate or 25.73 m3⁄min.
The temperature of the air flowing over the evaporator falls by 8 degrees.
(a) Sketch the cycle on Pressure-specific enthalpy and temperature-specific entropy diagrams, inserting the values on the pressure and temperature axes. (4)
(b) Calculate EACH of the following:
(i) the compressor power; (4)
(ii) the coefficient of performance: (2)
(iii) The volume of air flowing over the evaporator;(3)
(iv) the temperature rise of air over the condenser. (3)
Note: for air Cp=1.005 kJ⁄(kg K), density = 1.177 kg⁄m3
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