Refrigeration & Air Conditioning - Dec 2013
Mechanical Engineering (Semester 8)
TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.
Solve any four:
1 (a) Draw a schematic diagram of standard vapour compression system and explain the cycle using P-H/T-S diagram(5 marks)
1 (b) Explain types of refrigerants. Discuss the numbering system for refrigerants with few examples(5 marks)
1 (c) Define the term 'Effective Temperature'. Explain the factors affecting it.(5 marks)
1 (d) Explain the working of cooling Tower and define the terms Approach and 'Range' and 'Tower efficiency'.(5 marks)
1 (e) Define the term 'By-Pass factor' used for heating and cooling coil. Also explain factors affecting BPF.(5 marks)
2 (a) A dense air refrigeration machine operators on reversed Brayton cycle and is required for 10 TR capacity. The cooler pressure is 4.2 bar and the refrigerator pressure is 1.4 bar. The air is cooled in the cooler to a temperature of 50°C and the temperature of air inlet to compressor is-20°C. Determine for the ideal cycle:
i) C.O.P ii) Mass of air circulated per min. Iii) Theoretical piston displacement of compressor and expander iv) Net Power per TR.
Show the cycle on P-V and T-S diagram.
C for Air, Take γ=1.4, Cp=1 kJ/kgK)(12 marks) 2 (b) What do you understand by 'Defrosting' ? Classify defrosting methods and explain the working of any one defrosting methods with the help of neat diagram.(8 marks) 3 (a) A R-22 vapour compression system includes a liquid to vapour heat exchanger in the system. A system of capacity 70kW operates between - 8°C and 42°;C respect. Refrigerant is subcooled by 5°C and superheated by 10°C before entering the compressor. If a four cylinder single acting reciprocating compressor with bore to stroke ration 1:12 and operating at 1200 RPM is used. Determine
i)Ideal cap ii) COP of system
iii) Mass flow rate of refrigerant iv) Theoretical piston displacement per min
v) Bore and stroke of compressor
Assume volumetric efficiency of compressor=80%,
Cpl=1.24kj/kgk, Cpv=0.74 kj/kgk
Refrigerant properties given below:
|Temp. °C||Specific Volume m3/kg||Enthalpy kJ/kg||Entropy kJ/kg k|
i) Relative Humidity
ii) Dew point temperature.
Assume that condition of atmospheric air is 30°C and 55%RH and pressure is 1.0132 bar.(8 marks) 4 (b) Describe how solid CO2 is manufactured in detail.(12 marks) 5 (a) An air conditioned auditorium is to be maintained at 27°C dry bulb temperature and 60% R.H. The ambient condition is 40°C dry bulb temperature and 30°C well bulb temperature. The total sensible heat load is 100000 kJ/hr and the total latent heat load is 40000 kJ/hr. 60% of the return air is recirculated and mixed with 40% of make-up air after the cooling coil. The condition of air leaving the cooling coil is at 18°C.
Determine i)RSHF ii) Condition of air entering the auditorium iii) Amount of show the process on the Psychometric chart.(12 marks) 5 (b) A rectangular duet section of 500mm × 350mm size carries 75m3/min of air having density of 1.15kg/m3. Determine the equivalent diameter of a circular duct if-
i) The quantity of air carried in both the cases is same and
ii) The velocity of air in both the cases is same.
If f=0.01 for sheet metal, find the pressure loss, per 100m length of duct.(8 marks) 6 (a) Explain with neat sketches various expansion devices.(10 marks) 6 (b) Explain various duct design methods with a neat sketch of Friction chart.(10 marks)
Write short notes any four of the following:
7 (a) Deep sea water air conditioning.(5 marks) 7 (b) Commercial ice manufacturing.(5 marks) 7 (c) Thermostat Types and explain any one type with sketch.(5 marks) 7 (d) Air filters- Types and explain any one type with sketch.(5 marks) 7 (e) Aircraft air refrigeration system-types and explain any one type in brief with sketch.(5 marks)