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Fundamentals of Refrigeration and Air Conditioning, Assignments of Electronics

Various aspects of refrigeration and air conditioning, including definitions, thermodynamic properties, refrigeration cycles, and system components. It also includes theory questions and numerical problems related to refrigeration systems.

Typology: Assignments

2019/2020

Uploaded on 09/24/2020

harekrishna-ray
harekrishna-ray 🇮🇳

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REFRIGERATION AND AIRCONDITIONING
Objectives
1. Define: Refrigeration [1]
2. Define: Tonnage of Refrigeration [1]
3. Define COP of Refrigeration and give the equation for the same for VCR system
with proper notations [2]
4. Prove: 1 TR = 3.15 kJ/s [2]
5. Prove: (COP)
heat
pump
= 1+ (COP)
refrigerat
or
[2]
6. In a refrigerating machine, if the lower temperature is fixed, then the COP of the
machine can be increased by _____________ [1]
7. The COP of reversed Carnot Cycle most strongly depends on___________ [1]
8. The efficiency of a Carnot heat engine is 80%. The COP of refrigerator working
on reversed Carnot cycle is _____ [1]
9. The COP of reversed Carnot Refrigerator is 4. The ratio of its highest temperature
to lowest temperature is ______ [1]
10.
Air refrigeration cycle is used in _________ [1]
11.
In a refrigerating machine heat rejected is __________ than heat absorbed. [1]
12.
During refrigeration heat is rejected by the refrigerant in a __________ [1]
13.
In a VCR system the condition of the refrigerant before entering the condenser is
__________ [1]
14.
The highest temperature during the cycle in a VCR system occurs after
_________ [1]
15.
The lowest temperature during the cycle in a VCR system occurs after _________ [1]
16.
In a domestic refrigerator commonly used refrigerant is __________ [1]
17.
In a VAR system the compressor unit is replaced by ____, _____, and _____ [1]
18.
The COP of a practical VCR system is ________ as compared to VAR system [1]
19.
In aqua-ammonia and Li-Br water absorption refrigeration systems, the refrigerant
are respectively __________ and ___________ [1]
20.
In Li-Br water absorption refrigeration system ________ is used as refrigerant. [1]
21.
In aqua-ammonia absorption refrigeration system ________ is used as absorbent. [1]
22.
The refrigerant R-717 is_____________ [1]
23.
Chemical formula for R-12 is ______ [1]
24.
Dichloro-trifluoroethane is written as __________ [1]
25.
The refrigerant supplied to compressor must be_____________ [1]
26.
A condenser is used in the ____________ pressure side of a refrigerating system. [1]
27.
A evaporator is used in the ___________pressure side of a refrigerating system. [1]
28.
An evaporator is also known as______ [1]
29.
Capillary tube is an example of _________ [1]
30.
Throttling is an _________ process [1]
31.
In a refrigerating system expansion device is connected between ____ & _____ [1]
32.
In domestic refrigerator commonly used expansion device is _________ [1]
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REFRIGERATION AND AIRCONDITIONING

 Objectives

1. Define: Refrigeration [1]

2. Define: Tonnage of Refrigeration [1]

3. Define COP of Refrigeration and give the equation for the same for VCR system

with proper notations

[2]

4. Prove: 1 TR = 3.15 kJ/s [2]

5. Prove: (COP)heat pump = 1+ (COP)refrigerator [2]

6. In a refrigerating machine, if the lower temperature is fixed, then the COP of the

machine can be increased by _____________

[1]

7. The COP of reversed Carnot Cycle most strongly depends on___________ [1]

8. The efficiency of a Carnot heat engine is 80%. The COP of refrigerator working

on reversed Carnot cycle is _____

[1]

9. The COP of reversed Carnot Refrigerator is 4. The ratio of its highest temperature

to lowest temperature is ______

[1]

10. Air refrigeration cycle is used in _________ [1]

11. In a refrigerating machine heat rejected is __________ than heat absorbed. [1]

12. During refrigeration heat is rejected by the refrigerant in a __________ [1]

13. In a VCR system the condition of the refrigerant before entering the condenser is

__________

[1]

14. The highest temperature during the cycle in a VCR system occurs after

_________

[1]

15. The lowest temperature during the cycle in a VCR system occurs after _________ [1]

16. In a domestic refrigerator commonly used refrigerant is __________ [1]

17. In a VAR system the compressor unit is replaced by ____, _____, and _____ [1]

18. The COP of a practical VCR system is ________ as compared to VAR system [1]

19. In aqua-ammonia and Li-Br water absorption refrigeration systems, the refrigerant

are respectively __________ and ___________

[1]

20. In Li-Br water absorption refrigeration system ________ is used as refrigerant. [1]

21. In aqua-ammonia absorption refrigeration system ________ is used as absorbent. [1]

22. The refrigerant R-717 is_____________ [1]

23. Chemical formula for R-12 is ______ [1]

24. Dichloro-trifluoroethane is written as __________ [1]

25. The refrigerant supplied to compressor must be_____________ [1]

26. A condenser is used in the ____________ pressure side of a refrigerating system. [1]

27. A evaporator is used in the ___________pressure side of a refrigerating system. [1]

28. An evaporator is also known as______ [1]

29. Capillary tube is an example of _________ [1]

30. Throttling is an _________ process [1]

31. In a refrigerating system expansion device is connected between ____ & _____ [1]

32. In domestic refrigerator commonly used expansion device is _________ [1]

 Theory Questions

  1. What is the difference between Refrigerator and Heat Pump? Derive the expression for the Performance factor for both if they run on reversed Carnot cycle.

[6]

  1. Describe the mechanism of a simple VCR system. [6]
  2. Explain with reference to ph- diagram, the stages involved in vapour compression process of refrigeration. Establish the expression for the COP.

[6]

  1. What is the basic function of compressor in VCR system? How this function is achieved in VAR system?

[6]

  1. Draw a neat sketch of simple VAR system and explain the working for the same. [6]
  2. Discuss the advantages of VAR system over VCR system. [6]
  3. Enlist the desirable properties of a refrigerant. [6]
  4. Explain the construction and working of a window air conditioner. [6]
  5. Explain the construction and working of split AC. [6]
  6. Differentiate VCR and VAR system. [6]
  7. Explain the nomenclature method of a refrigerant giving three examples. [6]

 Numericals

  1. A machine working on carnot cycle operates between 305 K and 260 K. Determine the COP when it is operated as refrigerator, heat pump, and heat engine.

[6]

  1. A Carnot refrigeration cycle absorbs heat at 270 K and rejects it at 300 K:
    1. Calculate COP for this system.
    2. If the cycle is absorbing 1130 kJ/min at 270 K, how many kJ of work is required per second?
    3. How many kJ/min will the heat pump deliver at 300 K if it absorbs 1130 kJ/min at 270 K.

[6]

  1. A cold storage is maintained at -5oC while the surroundings are at 35oC. The heat leakage from the surroundings into the cold storage is 29 kW. Find the power required to drive the system.

[6]

  1. A refrigerator using carnot cycle requires 1.25 kW per Tonne of Refrigeration to maintain a temperature of -30oC. Find the COP of Carnot Refrigerator, Temperature at which the heat is rejected, and heat rejected per tonne of refrigeration.

[6]

  1. A refrigerating plant requires to produce 2.5 Tonnes of ice per day at -4oC from water at 20oC. If the temperature range in the compressor is between 25oC and –6oC, calculate the power required to drive the compressor. Latent heat of Ice is 335 kJ/kg and specific heat of ice is 2.1 kJ/kg.

[6]

  1. A carnot refrigeration system has working temperature of -30oC and 40oC. What is the maximum COP possible? If the actual COP is 75% of the maximum, calculate the actual refrigerating effect produced per kW/hr.

[6]

  1. In an ammonia vapour compression refrigeration system, the pressure in the evaporator is 2 bar. Ammonia at exit to evaporator has dryness 0.85and at entry has dryness 0.19. During compression work done per kg of ammonia is 150 kJ. Calculate the COP and the volume of vapour entering the compressor per minute, if the rate of ammonia circulation is 4.5 kg//min. The latent heat and specific volume at 2 bar are 1325 kJ/kg and 0.58 m^3 /kg respectively.

[6]

  1. The temperature limits of an ammonia refrigerating system are 25oC and -10oC. If the gas is 0. dry at the entry to compressor and dry at the exit to compressor. Calculate the COP of the cycle.

[6]