JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III REFRIGERATION AND AIR CONDITIONING Previous Question Paper (November/December - 2020 - R16)

An air refrigerator working on the principle of Bell-Coleman cycle. The air into the compressor is at 1 atm at -10°C. It is compressed to 10 atm and cooled to 40°C at the same pressure. It is then expanded to 1 atm and discharged to take cooling load. The air circulation is 1 kg/s. The isentropic efficiency of the compressor = 80%. The isentropic efficiency of the expander = 90%. Find the following:

A dense air refrigeration machine operating on Bell-Coleman cycle operates between 3.4 bar and 17 bar. The temperature of air after the after the cooler is 15°C and after the refrigerator is 6°C. For a refrigeration capacity of 6 tonnes, find:

A simple saturation cycle using F12 is designed for taking a load of 10 tones. The refrigerator and ambient temperatures are -10°C and 30°C respectively. A minimum temperature difference of 5°C is required in evaporator and condenser for heat transfer. Find:

A refrigerating plant of 28 kW capacity has its evaporation temperature -8°C and condenser temperature of 30°C. The refrigerant, R-12 is sub-cooled 5°C before entering the expansion valve and the vapour is superheated 6°C before leaving the evaporator coil. The compression of the refrigerant in the compressor is isentropic. If there is a suction pressure drop of 0.2 bar through the valves; and discharge pressure drop through the valve of 0.1 bar, determine the C.O.P. of the plant, theoretical piston displacements/min and the heat removed in the condenser. Solve the problem with the help of P-h chart. Give also a diagrammatic sketch of this cycle on the T-s chart.