1
Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
PDDC SEMESTER-VII EXAMINATION WINTER 2018
Subject Code:X71901 Date: 15/11/2018
Subject Name: Refrigeration and Air-conditioning
Time: 10:30 AM TO 01:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1

What is refrigeration? Derive an expression of COP for Bell-Coleman air refrigeration cycle. Also show the process p-V and T-s diagram.
07

What is refrigeration? State the advantages of air cycle for air craft refrigeration.
07
Q.2

What is refrigerant? State the desirable characteristics of good refrigerant.
07

Explain the vapour compression cycle with superheated vapour before compression with suitable diagram.
07
OR

What is compound vapour compression refrigeration system? State the advantages and disadvantages of the same.
07
Q.3

Explain with neat sketch working of two stage vapour compression system with flash intercooler. Also derive suitable formula.
07

In a 15 TR Ammonia refrigeration plant, the condensing temperature is 25o C and evaporation temperature -10o C. The refrigerant ammonia is sub-cooled by 5o C before passing through the throttle valve. The vapour leaving the evaporator is 0.97 dry. Find: coefficient of performance, and power required. Use the following properties of ammonia:
Saturation
Temperature oC
Specific enthalpy
kJ/kg
Specific entropy
kJ/kg K
Specific heat
kJ/kg K
Liquid
Vapour
Liquid
Vapour
Liquid
Vapour
25
298.9
1465.84
1.1242
5.0391
4.60
2.80
-10
135.37
1433.05
0.5442
5.4770


07
OR
Q.3

Compare vapour absorption and vapour compression refrigeration system.
07

Draw a line diagram of Electrolux refrigerator and explain its working. What is the important role of hydrogen in this refrigeration system?
07
Q.4

Explain dry expansion type evaporator with neat sketch.
07

What is the principle of operation of steam jet refrigeration? Explain the working of the same with neat sketch.
07
OR
Q.4

Define the following:
Effective room sensible heat factor, Wet bulb depression,
bypass factor, Relative humidity, Dew point temperature, Degree of saturation. sensible heat factor.
07
2

50 m3 of air per minute at 30o C dry bulb temperature and 20o C wet bulb temperature is passed over the cooling coil whose surface temperature is 5o C. The coil cooling capacity is 3.5 tons of refrigeration under the given condition of air. Determine DBT and WBT of air leaving the cooling coil, the bypass factor, and amount of water condensed at coil.
07
Q.5

What is sensible and latent heat load? Explain total equivalent temperature difference.
07

Explain equal friction method of duct design. State its advantages and disadvantages.
07
OR
Q.5

Explain all air central air conditioning system briefly.
07

State the various dehumidifier and explain any one in detail with neat sketch.
07