1
Seat No.: Enrolment
GUJARAT TECHNOLOGICAL UNIVERSITY
PDDC SEMESTER VII- EXAMINATION SUMMER 2017
Subject Code: X71901 Date: 27/04/2017
Subject Name: Refrigeration and Air Conditioning
Time: 02.30PM to 05.00PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
4. Use of Refrigerant and psychometric chart is permitted.
Q.1

Discuss in detail about the Desirable Properties of Refrigerant
07

Explain the working principle and Construction of practical H2O-NH3 vapour absorption refrigeration (Aqua Ammonia) system with neat sketch.
07
Q.2

In a Refrigeration plant working on Bell-Coleman cycle, Air is compressed to 5 bar from 1 bar. Its initial temperature is 10° C. After compression air is cooled up to 20° C in a cooler before expanding back to a pressure of 1 bar. Determine the theoretical COP of the plant and net refrigerating effect. Take Cp =1.005 kJ/kg K and Cv =0.718 kJ/kg K
07

Discuss the advantages and disadvantages of air refrigeration system used for air
Crafts.
07
OR

Explain the working of boot-strap air refrigeration system with neat schematic. Also represent it on t-s diagram.
07
Q.3

Draw and Explain in Detail the actual vapour compression refrigeration system on p-h and t-s diagrams.
07

The following data refers to a 20 TR ice plant using NH3 as Refrigerant:
The temperature of water entering and leaving the condenser are 20° C and 27° C and temperature of brine in the evaporator is C. Before entering the expansion valve, NH3 is cooled to 20° C and NH3 enters the compressor dry saturated.
Calculate for 1 TR, the power expended, amount of cooling water in condenser and COP of the Plant. Use the Properties given in the table below
Tsat, C
Enthalpy kJ/kg
Entropy kJ/kg K
Sp.Heat kJ/kg K
hf
hg
Sf
Sg
Cpl
Cpg
-15
112.34
1426.54
0.4572
5.5490
4.396
2.303
25
298.90
1465.84
1.1242
5.0391
4.606
2.805
07
OR
Q.3

Explain compound compression with flash chamber but without intercooler with system diagram and p-h diagram.
07

A single compressor using R12 as refrigerant has three evaporators of capacity 10 TR, 20 TR and 30 TR .All the evaporators operate at C and the vapours leaving the evaporators are dry saturated. The condenser temperature is 40 C. The liquid refrigerant leaving the condenser is subcooled to 30° C. Assuming isentropic compression. Find: the mass of refrigerant flowing through each evaporator, the power required to drive the compressor and COP of the system.
Use p-h diagram of
07
2
Q.4

Explain following terms briefly:
Dew point temperature Wet bulb temperature Specific humidity Relative humidity Degree of saturation Comfort Air-conditioning Effective temperature.
07

The atmospheric air at 760 mm of Hg, dry bulb temperature 15° C and wet bulb temperature 11° C enters a heating coil whose temperature is 41° C. Assuming by-pass factor of heating coil as 0.5, determine dry bulb temperature wet bulb temperature and relative humidity of the air leaving the coil. Also determine the sensible heat added to the air per kg of dry air.
Use psychometric chart)
07
OR
Q.4

What do you mean by duct? Classify the duct. Discuss in brief about Economic considerations in selection of duct.
07

The amount of air supplied to an air conditioned hall is 300 m3/min. The atmospheric conditions are 35° C DBT and 55 RH. The required conditions are 20° C DBT and 60 RH. Find out the sensible heat and latent heat removed from the air per minute. Also find sensible heat factor for the system.
Use psychometric chart)
07
Q.5

Short note on thermostatic expansion valve
07

Draw and Explain the working of a steam-jet refrigeration system with neat sketch.
07
OR
Q.5

Explain the working of window room air conditioner with a schematic. How split air conditioner differs from it?
07

Explain the procedure for calculating cooling load due to infiltration air.
07