Q6. A vapour compression refrigeration plant using ammonia is used is used to maintain the temperature of a cold room at -25℃ when the ambient conditions are 30℃.
The cold room bulkheads have an overall thermal conductivity of 0.5 W/m2K and a total surface area of 162 m2.
The ammonia enters the compressor as a dry saturated vapour at -28℃ and leaves at a pressure and temperature of 9.134 bar and 122℃. It enters the expansion valve at a temperature of 22℃.
The two-cylinder single acting compressor has a bore of 76 mm and a stroke of 80 mm and runs at a speed of 320 rev/min.
(a) Sketch the cycle on a Temperature specific entropy diagram showing ALL the temperature. (3)
(b) Calculate EACH of the following:
(i) The cooling load; (2)
(ii) The cycle coefficient of performance;(4)
(iii) The Carnot cycle coefficient of performance when operating between the same pressure; (2)
(iv) The volumetric efficiency of the compressor. (5)
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