In order to keep off foodstuff in better condition, a food storage locker requires 20 tons of refrigeration. The evaporator temperature is –8°C and the condenser temperature is 30°C. The refrigerant used in the refrigeration plant is Fr-12. This is subcooled by 5°C before entering to the expansion valve. The vapor is superheated to 6°C before leaving the evaporator coil. The compressor employed is of two cylinder, single-acting having stroke equal to 1.5 times the bore. The speed of the compressor is 900 r.p.m. The compression process may be assumed to be isentropic. Work out the following:
(i) Sketch the system and show the process on T-S and p-h diagrams
(ii) The refrigerating effect per kg of refrigerant
(iii) The mass flow rate of the refrigerant circulated
(iv) The theoretical piston displacement
(v) The power input to compressor if mechanical efficiency is 0.9.
(vi) The coefficient of performance
(vii) The bore and stroke if volumetric efficiency is 90%.
Use the following properties for the solution:
h1 = 356 kJ/kg h2 = 377 kJ/kg
hf3 = h4 = 225.5 kJ/kg v1 = 0.077 m3/kg
Where, 1, 2, 3 and 4 refer to inlet to compressor, outlet of compressor, exit of subcooler and capillary tube/expansion valve exit respectively.