Refrigeration & Air Conditioning-Engineering-Nov2019 - Grad Plus

Refrigeration & Air Conditioning-Engineering-Nov2019

T.E. (Mechanical)
(2015 Pattern) (Semester – II)

Time : 2½ Hours
Max. Marks : 70
Instructions to the candidates:
1) All question are compulsory.
2) Neat diagrams must be drawn wherever necessary.
3) Assume suitable data if necessary and mention it clearly.
4) Use of steam table and psychrometric chart is allowed.

Q1) a) Explain automotive air conditioning with its components and their function in brief. [4M]

b) Write any four eco-friendly refrigerants with their chemical formula and designation. [6M]


Q2) a) Explain aqua ammonia vapour absorption refrigeration system with schematic diagram. [4M]

b) An ideal vapour compression refrigerator uses methyl chloride (R40) as a refrigerant and operates between temperature limits of —10 °C and 45 °C. At entry to the compressor, the refrigerant is dry saturated and after compression it acquires a temperature of 60°C. There is no under-cooling. Find the COP of the refrigerator. Take CPV = 1.09 kJ/kg.K Draw p-h diagram of the cycle. [6M]
The relevant properties of methyl chloride(R40) are as follows:

Sat. Temphfhfsfsg

Q3) a) Compare vapour compression refrigeration system and vapour absorption system on any four criterion. [4M]

b) In an absorption type refrigerator, the heat is supplied to generator by condensing steam at 1.6 bar dry and saturated. The refrigeration temperature is –5 °C. Condensation takes place at 30 °C. Find maximum
possible COP of the system. If the refrigeration load is 150 TR and actual COP is 80% of maximum COP, calculate the mass of steam required per hour.
Use Tsat 113.3°C, hfg 2220.9 kJ/kg at 1.6 bar [6M]


Q4) a) Draw schematic and p-h diagram cascade refrigeration system and explain its working. [6M]

b) Why is flash gas intercooling is used in multistage compression. Explain it’s any two advantages. [4M]

Q5) a) Define specific humidity, relative humidity and by-pass factor. [6M]

b) The pressure of the air entering and leaving the adiabatic saturator is 1 bar. The air enters at 30 °C and leaves as saturated air at 20 °C. The specific humidity of entering steam of air is 0.0107 kg/kg of dry air. Calculate the specific humidity, relative humidity of exit the air- vapour mixture. [10M]


Q6) a) Write a note on indoor air quality requirement. [4M]

b) What is infiltration? [2M]

c) The atmospheric air at 25 °C DBT and 2 °C WBT is flowing at a rate of 100 m3/min through a duct. The dry saturated steam at 100°C is injected into the air stream at a rate of 72 kg/h. Calculate the specific humidity, DBT, WBT, relative humidity and enthalpy of air leaving the duct. Show the process on psychrometric chart. [10M]

Q7) a) Explain with neat sketch winter air conditioning system. [6M]

b) Explain with neat sketch capillary tube. [6M]

c) Explain with neat sketch working of thermostat. [6M]


Q8) a) Explain variable air volume system. State any two advantages over constant air volume system. [6M]

b) Explain with neat sketch water cooled condenser. [6M]

c) Draw p-v diagram of single acting single stage reciprocating compressor and explain its working in brief. [6M]

Q9) a) Explain any two duct shapes with sketches and list any four duct materials. [6M]

b) A rectangular duct, 800 mm x 550 mm size carries 5m3/s of air having density 1.15 kg/m3. Determine equivalent diameter of circular duct if
a) Air flow is same.
b) Air velocity is same.
Further find pressure loss per 100 m for F = 0.001. Also calculate total pressure required at inlet to the duct to maintain the same flow, and air power required. [10M]


Q10) a) Explain any two types of filters used in air conditioning system. [4M]

b) Explain any two types of supply air outlets with suitable diagrams. [6M]

i) Grille outlets
ii) Ceiling diffuser outlets
iii) Slot diffuser outlets

c) Explain equal friction method of duct design [6M]

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