Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 6th Sem New 2161908 Refrigeration And Air Conditioning Previous Question Paper
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI (NEW) EXAMINATION ? WINTER 2018
Subject Code:2161908 Date:15/12/2018
Subject Name:Refrigeration and Air Conditioning
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) What are the limitations of Carnot cycle for air refrigeration? 03
(b) Define: Refrigeration, Dry Bulb Temperature, COP, Saturated air. 04
(c) Explain Electrolux refrigerator with line diagram. 07
Q.2 (a) Explain use of hygrometer and sling psychrometer. 03
(b) In a Bell-Coleman refrigeration plant, the air is drawn from cold chamber
at 1 bar and 15? C and compressed to 6 bar. Then air is cooled to 28? C
in the cooler before expanding in the expander to the cold chamber
pressure of 1 bar. The compression and expansion processes are
isentropic. Calculate: 1) COP of the plant, 2) Refrigerating effect per kg
of air.
Assume for air ? = 1.4 and Cp = 1.005 kJ/kgK
04
(c) An ammonia vapour compression refrigeration system produces 10 ton
of ice from and at 0? C in a day. The system is operating between pressure
limits of 2.9 bar and 12.3 bar. The ammonia vapour is dry and saturated
at the end of compression. Calculate : (1) Mass flow rate of refrigerant
and (2) Power required to drive the compressor.
Assume (COP)act = 60 % of (COP)ideal.
For ice L = 330 kJ/kg, for water Cp = 4.187 kJ/kgK
Use following properties for Ammonia
Pressure
(bar)
Saturation Temp
(?C)
Specific enthalpy
(kJ/kg)
Specific Entropy
(kJ/kg K)
Liquid Vapour Liquid Vapour
2.9
-10
154.01 1450.7 0.8293 5.7569
12.3
+32
351.45 1487.11 1.5196 5.2412
07
OR
(c) An aircraft simple air refrigeration system having a load of 10 TR. The
atmospheric pressure and temperature are 0.92 bar and 15 ?C
respectively. The pressure after ramming process is 1.015 bar. The air is
cooled by 52 ?C in the heat exchanger. The cabin pressure is 1 bar and
temperature of air leaving the cabin is 24 ?C. Calculate i) mass of air
circulated per minute, ii) Power required to take the load of cooling in
the cabin, iii) COP of the system.
Assume compression and expansion processes are isentropic and
pressure ratio in main compressor is 4.
07
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?VI (NEW) EXAMINATION ? WINTER 2018
Subject Code:2161908 Date:15/12/2018
Subject Name:Refrigeration and Air Conditioning
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
MARKS
Q.1 (a) What are the limitations of Carnot cycle for air refrigeration? 03
(b) Define: Refrigeration, Dry Bulb Temperature, COP, Saturated air. 04
(c) Explain Electrolux refrigerator with line diagram. 07
Q.2 (a) Explain use of hygrometer and sling psychrometer. 03
(b) In a Bell-Coleman refrigeration plant, the air is drawn from cold chamber
at 1 bar and 15? C and compressed to 6 bar. Then air is cooled to 28? C
in the cooler before expanding in the expander to the cold chamber
pressure of 1 bar. The compression and expansion processes are
isentropic. Calculate: 1) COP of the plant, 2) Refrigerating effect per kg
of air.
Assume for air ? = 1.4 and Cp = 1.005 kJ/kgK
04
(c) An ammonia vapour compression refrigeration system produces 10 ton
of ice from and at 0? C in a day. The system is operating between pressure
limits of 2.9 bar and 12.3 bar. The ammonia vapour is dry and saturated
at the end of compression. Calculate : (1) Mass flow rate of refrigerant
and (2) Power required to drive the compressor.
Assume (COP)act = 60 % of (COP)ideal.
For ice L = 330 kJ/kg, for water Cp = 4.187 kJ/kgK
Use following properties for Ammonia
Pressure
(bar)
Saturation Temp
(?C)
Specific enthalpy
(kJ/kg)
Specific Entropy
(kJ/kg K)
Liquid Vapour Liquid Vapour
2.9
-10
154.01 1450.7 0.8293 5.7569
12.3
+32
351.45 1487.11 1.5196 5.2412
07
OR
(c) An aircraft simple air refrigeration system having a load of 10 TR. The
atmospheric pressure and temperature are 0.92 bar and 15 ?C
respectively. The pressure after ramming process is 1.015 bar. The air is
cooled by 52 ?C in the heat exchanger. The cabin pressure is 1 bar and
temperature of air leaving the cabin is 24 ?C. Calculate i) mass of air
circulated per minute, ii) Power required to take the load of cooling in
the cabin, iii) COP of the system.
Assume compression and expansion processes are isentropic and
pressure ratio in main compressor is 4.
07
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2
Q.3 (a) List out factors affecting human thermal comfort and explain any one. 03
(b) State and explain various heat loads to be considered for cooling load
calculation of typical building.
04
(c) 50 m
3
of air per minute at 30? C DBT and 20? C WBT is passed over the
cooling coil whose surface temperature is 5? C. The cooling coil capacity
is 3.5 tones of refrigeration under the given condition of air. Determine
DBT and WBT of air leaving the cooling coil, the bypass factor and water
condensed at coil.
07
OR
Q.3 (a) How are refrigerants classified? 03
(b) Represent following processes on psychrometric chart
1) Sensible cooling, 2) Dehumidification, 3) Heating with
humidification, 4) Chemical dehumidification
04
(c) Explain vapour compression refrigeration cycle with superheated
refrigerant before compression with p-h and T-s diagram.
07
Q.4 (a) How will you assign number to the refrigerants: Dichloro difluoro
methane and dichloro tetra fluoro ethane ?
03
(b) Discuss application of refrigeration in food industries. 04
(c) Explain practical vapour absorption refrigeration system with schematic
diagram.
07
OR
Q.4 (a) Advantages of vapour compression system over air refrigeration system. 03
(b) Explain working of cascad refrigeration system. 04
(c) Explain in brief the following: i) Filters, ii) Humidifiers used in air
conditioning systems.
07
Q.5 (a) Explain velocity reduction method with advantages and disadvantages. 03
(b) Explain with neat sketch working of hermetically sealed compressor. 04
(c) Explain all water central air conditioning system with diagram. 07
OR
Q.5 (a) Write short note on split air conditioner. 03
(b) Explain working of flooded type evaporator with neat sketch. 04
(c) Explain difference between all air system and all water system? What are
the advantages of all water system compared to all air system?
07
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This post was last modified on 20 February 2020