MU Mechanical Engineering (Semester 8)
Total marks: --
Total time: --
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary
1.a. Explain difference between vapour compression refrigeration system and vapour absorption refrigeration system.
1.b. Explain the need of aircraft refrigeration. Draw reduced ambient air refrigeration cycle with neat schematic an T-S diagram.
1.c. Define the term 'by pass factor' used for heating and cooling coil.
1.d. What is the difference between heat pump and refrigerator. Derive the relationship for COP between refrigerator and heat pump.
2.a. Explain the working of simple vapour compression cycle with schematic and p-h and T-s diagrams.
2.b. 100kW power is used for refrigeration system working on bootstrap air refrigeration cycle. Required data are given below:
Ambient air pressure = 1bar
Ambient air temperature = 288K
Compressor delivery pressure = 3.5bar
Cabin pressure = 1 bar
Maximum pressure = 5.6bar >br> Heat exchanger effectiveness for both heat exchanger = 0.85
Efficiency of main and auxiliary compressor is 0.83 and 0.75 resp.
Turbine effieciency = 0.77
Cabin is maintained at 28°C and 1 bar
i) Refrigeration capacity in TR
iii) Determine the percentage of turbine power used by auxillary compressor.
3.a. Explain the ozone depletion and global warming issues. Discuss desirable properties of good refrigerant and designation of refrigerant with example.
3.b. A food storage locker has a capacity of 12 TR and operates between the evaportation temperature of -8°C and condenstion temeprature of 30°C. The refrigerant R-12 is sub-cooled by 5°C before throttling and the vapour is superneated by 2°C before leaving the evaporator. Assuming a twin cylinder single acting compressor running at 1000 RPM with L:D ratio 1.5.. Calculate:
i) COP os system
ii) Specific power required
iv) Stroke compressor having volumetric efficiency of 0.945 Draw p-h and T-s diagram.
4.a. What are the types of expansion valves? Explain the working of the thermostatic expansion valve.
4.b. The design conditions for an air conditions for an air conditioned hall are:
Inside condition 24°C, 60% RH
Outside 38°C DBT, 28°C WBT
Sensible heat gain = 45kW
Latent heat gain = 11.25kW
Infiltrated air = 1200m3/h
Coil ADP = 10°C
60% total air is re-circulated and mixed with conditioned air after cooling coil. Find
i) Condition of air entering hall
ii) Refrigeration load.
5.a. What is aspect ratio? Discuss the different methods of duct design.
5.b. Explain Li-Br Water vapour absorption system with neat sketch.
5.c. Explain briefly types of condensers.
6. Write short note any five question
6.a. Cooling tower performance and selection
6.b. Air conditioning and human comfort
6.c. Deep sea water air conditioning
6.d. Dairy process plant
6.e. Types of psychrometric processes
6.f. Steam jet refrigeration
6.g. Controls used in Refrigeration and Air Conditioning.