Q6. In the refrigeration plant shown in Fig Q6, A surface heat exchanger is used to cool the liquid entering the expansion valve. The operation of the heat exchanger may be considered to be adiabatic.
The refrigerant is ammonia and the compressor suction and discharge pressures are 2.465 bar and 11.67 bar respectively. The refrigerant leaves the condenser as a saturated liquid and enters the expansion valve at a temperature of 18℃.
At the evaporator outlet, the refrigerant is a dry saturated vapour.
During compression the specific entropy increases by 0.24 %.
(a) Calculate EACH of the following:
(i) The compressor suction temperature; (4)
(ii) The dryness fraction of the refrigerant entering the evaporator; (2)
(iii) The coefficient of performance of the cycle; (4)
(iv) The reversed Carnot cycle COP for the same pressure.(2)
(b) Sketch a Temperature-specific entropy diagram showing:
(i) The actual cycle;(2)
(ii) The reversed Carnot cycle operating between the same pressures;(1)
(iii) Irreversible processes as dash line. (1)
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