Jawaharlal Nehru Technological University Hyderabad B. Tech IV REFRIGERATION AND AIR CONDITIONING Previous Question Paper (January/February - 2023 - R18)

An air craft moving with speed of 1000 km/h uses simple gas refrigeration cycle for air conditioning. The ambient pressure and temperature are 0.35 bar and -10°C respectively. The pressure ratio of compressor is 4.5. The heat exchanger effectiveness is 0.95. The isentropic efficiencies of compressor and expander are 0.8 each. The cabin pressure and temperature are 1.06 bar and 25°C. Determine temperature and pressures at all points of the cycle. Also find the volume flow rate through compressor inlet and expander outlet for 100 TR. Take C_p=1.005 kJ/kg K; R=0.287 kJ/kg K and C_p/C_v=1.4 for air.

Explain Boot strap evaporative cooling of air refrigeration system. Draw its schematic diagram and represent the processes on P-h and T-S diagrams. Write down the equations for calculating the power and COP of the system.

In an ammonia vapor compression refrigerator, the temperature is refrigerator is -10°C and temperature of NH₃ coming out of compressor is 30°C. The vapor is condensed in the condenser at 30°C. Find the theoretical C.O.P. of the cycle when the vapor at the end of compression is 0.9 dry. Latent heat of NH₃ at 30°C = 1442 kJ/kg. Specific heat of liquid NH₃ = 4.7 kJ/kg.

What are the differences between ideal and actual VCRS. Derive the expression for COP of actual VCRS.

A refrigerating plant works between -10°C evaporator temperature and 40°C condenser temperature when F-12 is used as refrigerant. A compressor used has 2 cylinders and the diameter and stroke of the cylinder are 56.5 mm and 50 mm respectively. If the clearance is 4% of the stroke and compressor runs at 1450 R.P.M., find the following: a) Refrigerating capacity of the plant b) Power required to run the compressor c) COP of the system. Take γ=1.13 for F-12.

In an absorption type refrigerator, the heat is supplied to NH₃ generator by condensing steam at 2 bar and 90% dry. The temperature to be maintained in the refrigerator is -5°C. The temperature of the atmosphere is 30°C. Find the maximum C.O.P. possible of the refrigerator. If the refrigeration load is 20 tons and actual C.O.P. is 70% of maximum C.O.P., find the mass of steam required per hour.

Atmospheric air at 35°C and 60% R.H. is conditioned to 22°C DBT and 55% R.H. This is done first by cooling and dehumidifying and then heating. If the quantity of air flow is 60 cu. m. per minute find the following. a) Mass of water drained. b) Capacity of cooling coil. c) Capacity of heating coil. Take p_t= 1.033 bar.