1. Course : B.Tech Mechanical
Subject : Elements of Mechanical
Engineering
Unit-4

2.  Introduction
 Principle & Application of Refrigeration
 Definitions of refrigeration
 Refrigerants and refrigerators
 Type of refrigeration systems
 Air conditioning
 Windows and splits air conditions
Refrigeration & Air Conditioning

3. Refrigeration
 The term refrigeration may be defined as the
process of removing heat from a substance
under controlled conditions.
 It also includes the process of reducing heat &
maintaining the temp. of a body below the
general temp. of its surroundings.
 In other words the refrigeration means a
continued extraction of heat from a body
whose temp is already below the temp. of its
surroundings.

4. Refrigeration Systems
 The mechanism used for lowering or
producing low temp. in a body or a space,
whose temp. is already below the temp. of its
surrounding, is called the refrigeration
system.
 Here the heat is being generally pumped from
low level to the higher one & is rejected at
high temp.
Introduction

5. How does it work?
High Temperature
Reservoir
Low Temperature Reservoir
R Work Input
Heat Absorbed
Heat Rejected
Principle of Refrigeration

6.  In chemical industries, for separating and
liquefying the gases.
 In manufacturing and storing ice.
 For the preservation of perishable food items in
cold storages.
 For cooling water.
 For controlling humidity of air manufacture and
heat treatment of steels.
 For chilling the oil to remove wax in oil
refineries.
 For the preservation of tablets and medicines in
pharmaceutical industries.
 For the preservation of blood tissues etc.,
 For comfort air conditioning the hospitals,
theatres, etc.,

7. Refrigerating Effect (N): It is defined as the
quantity of heat extracted from a cold body
or space to be cooled in a given time.
N= Heat extracted from the cold space
Time taken
Specific Heat of water and ice : It is the
quantity of heat required to raise or lower
the temperature of one kg of water (or ice),
through one kelvin or (10 c) in one second.
Specific heat of water, Cpw = 4.19 kJ/kg K
Specific heat of ice, Cpice = 2.1 kJ/kg K.

8. Capacity of a Refrigeration Unit :
 Capacity of a refrigerating machines are expressed
by their cooling capacity.
 The standard unit used for expressing the capacity
of refrigerating machine is ton of refrigeration.
 One ton of refrigeration is defined as, “the quantity
of heat abstracted (refrigerating effect) to freeze
(into ice) one ton of water in a duration of 24 hours
at 0o c”.
Heat extracted from at oo c = latent heat of ice
Latent heat of ice = 336 kJ/kg
i.e., 336 kJ of heat should be extracted one kg of
water at 0o C to convert it into ice.

9. One ton of refrigeration= 336x1000 kJ/24
hrs.
= 336x1000
kJ/min
24x60
One ton of refrigeration = 233.333 kJ/min
= 3.8889
kJ/sec
For calculation purpose,
One ton of refrigeration = 12600 kJ/hr
= 210
kJ/min
Ton of refrigeration = 3.5 kJ/s

10. Performance of Refrigerators (Co efficient of
Refrigerators) :
 The performance of heat engine is expressed
by its thermal efficiency.
 The performance of a refrigerator cannot be
expressed in terms of efficiency.
 In case of a refrigerator the aim is to extract
maximum quantity of heat from the sink with
minimum of work input.
 Hence a new term Co efficient of
Performance is brought into use to express
the performance of refrigerator.

11. Co efficient of Performance: It is defined as the
ratio of heat extracted in a given time
(refrigerating effect) to the work input.
Co efficient of performance = Heat extracted in evaporator
Work
Input
Co efficient of performance = Refrigerating Effect
Work
Input
Co efficient of performance = N
W
The COP is always greater than 1 and known as theoretical
coefficient of performance.

12. Any substance capable of absorbing heat
from another required substance can be used
as refrigerant i.e. ice ,water, brine, air etc.
Primary Refrigerant
Refrigerants:
Secondary Refrigerant
Refrigerants

13. Primary Refrigerant
 They take part directly in refrigerating
systems.
 Freon Ammonia , Carbon dioxide, Sulphur
dioxide etc.
Secondary Refrigerant
 First they are cooled by primary
refrigerants then they are circulated .
 Chilled water, brine solutions etc.
Refrigerants

14. Properties of Refrigerants
 Low Boiling Point
 Low Freezing Point.
 High Latent Heat.
 Chemically Inert & stable .
 Non Flammable
 Non toxic
 Should not react with lubrication oil of
comp.
 Should not be corrosive
Refrigerants

15. Important refrigerants
Refrigerant is the working fluid used in
refrigerators Commonly used refrigerants are:
1.Ammonia : used in ice plants, large cold storages, skating
rings etc.
2.Carbon dioxide : used in marine refrigerators, dry ice
making etc.
3.Methyl chloride: used in domestic & industrial
refrigerators (now obsolate)
4.Fluorocarbons : Freon -11,12,13,22,113,114, etc.
These are used in domestic & industrial
application. These chemicals damage the ozone
layer and hence they are being replaced.
Refrigerants

16. Properties of Ideal Refrigerants
 An ideal refrigerant should satisfy the
following thermodynamic , chemical &
physical requirements:
Thermodynamic properties.
 1. low boiling point
 2. high critical temperature & low critical
pressure.
 3.Freezing point should be lower than the
refrigeration system temperature to avoid
blocking of pipes.
Refrigerants

17. Properties of Ideal Refrigerants
Thermo physical properties.
 1. low viscosity.
 2. high thermal conductivity.
 3.high latent heat of vaporization.
 4.low specific volume.
 5.low specific heat.
Refrigerants

18. Chemical requirements of Ideal Refrigerants
1. Should be non inflammable.
2. It should not be toxic.
3. Should be non corrosive to metals.
4.Should be capable of mixing well with
lubricating oil.
5.Electric resistance should be high.
6.Leakage should be detected easily.
7.Should be odourless.
Refrigerants

19.  Ice Refrigerators : Ice is kept in the cabinet of
refrigerators and this acts as the refrigerating
means.
 Air Refrigerators : Air is used as working
agent in these types of refrigerators.
E.g., Bell Coleman Cycle.
 Vapour Refrigerators: The working agents
employed in this type of refrigerators are
ammonia, CO2, SO2, freons etc.,

20. Types of Refrigeration
• Vapour Compression
Refrigeration (VCR): uses
mechanical energy
• Vapour Absorption
Refrigeration (VAR): uses
thermal energy
Refrigeration systems

21. Types of Refrigeration
Vapour Compression Refrigeration
• Highly compressed fluids tend to get
colder when allowed to expand
• If pressure high enough
•Compressed air hotter than source
of cooling
•Expanded gas cooler than desired
cold temperature

22. Types of Refrigeration
Vapour Compression Refrigeration
Two advantages
• Lot of heat can be removed (lot of
thermal energy to change liquid to
vapour)
• Heat transfer rate remains high
(temperature of working fluid much
lower than what is being cooled)

23. Types of Refrigeration
Vapour Compression Refrigeration
Refrigeration cycle
1

24. Types of Refrigeration
Vapour Compression Refrigeration
Type of refrigerant
• Refrigerant determined by the
required cooling temperature
• Chlorinated fluorocarbons (CFCs) or
freons: R-11, R-12, R-21, R-22 and
R-502

25. Types of Refrigeration
Vapour Compression Refrigeration
Choice of compressor, design of
condenser, evaporator determined by
• Refrigerant
• Required cooling
• Load
• Ease of maintenance
• Physical space requirements
• Availability of utilities (water, power)

26. Types of Refrigeration
Vapour Absorption Refrigeration
Refrigeration cycle
2

27. In this system compression process of vapour
compression cycle is eliminated. Instead of
that the following three processes are carried
out.
1. Absorbing ammonia vapour into water.
2. Pumping this solution to a high pressure
cycle
3. Producing ammonia vapours from ammonia
solution by heating.
Vapour Absorption Refrigeration

28. Construction:
 The vapour absorption system consists of a
condenser, an expansion valve and an
evaporator.
 They perform the same as they do in vapour
compression method.
 In addition to these, this system has an
absorber, a heat exchanger, an analyser and
a rectifier.

29. Working:
1. Dry ammonia vapour at low pressure passes in
to the absorber from the evaporator.
2. In the absorber the dry ammonia vapour is
dissolved in cold water and strong solution of
ammonia is formed.
3. Heat evolved during the absorption of ammonia
is removed by circulating cold water through
the coils kept in the absorber.
4. The highly concentrated ammonia (known as
Aqua Ammonia) is then pumped by a pump to
generator through a heat exchanger.

30. Working:
6. In the heat exchanger the strong ammonia
solution is heated by the hot weak solution
returning from the generator to the
absorber.
7. In the generator the warm solution is further
heated by steam coils, gas or electricity and
the ammonia vapour is driven out of
solution.
8. The boiling point of ammonia is less than
that of water.
9. Hence the vapours leaving the generator are
mainly of ammonia.

31. Working:
9. The weak ammonia solution is left in the
generator is called weak aqua.
10. This weak solution is returned to the
absorber through the heat exchanger.
11. Ammonia vapours leaving the generator
may contain some water vapour.
12. If this water vapour is allowed to the
condenser and expansion valve, it may freeze
resulting in chocked flow.
13. Analyser and rectifiers are incorporated in
the system before condenser.

32. Working:
14. The ammonia vapour from the generator
passes through a series of trays in the analyser
and ammonia is separated from water vapour.
15. The separated water vapour returned to
generator.
16. Then the ammonia vapour passes through a
rectifier.
17. The rectifier resembles a condenser and water
vapour still present in ammonia vapour
condenses and the condensate is returned to
analyser.
18. The virtually pure ammonia vapour then
passes through the condenser.

33. Working:
19. The latent heat of ammonia vapour is rejected
to the cooling water circulated through the
condenser and the ammonia vapour is
condensed to liquid ammonia.
20. The high pressure liquid ammonia is throttled
by an expansion valve or throttle valve.
21. This reduces the high temperature of the
liquid ammonia to a low value and liquid
ammonia partly evaporates.
22. Then this is led to the evaporator.
23. In the evaporator the liquid fully vaporizes.

34. Working:
24. The latent heat of evaporation is obtained
from the brine or other body which is being
cooled.
25. The low pressure ammonia vapour leaving
the evaporator again enters the absorber and
the cycle is completed.
26. This cycle is repeated again to provide the
refrigerating effect.

35. S.No
.
Vapour Compression System Vapour Absorption System
1 This system has more wear
and tear and produces more
noise due to the moving parts
of the compressor.
Only moving part in this system
is an aqua pump. Hence the
quieter in operation and less
wear and tear
2. Electric power is needed to
drive the system
Waste of exhaust steam may be
used. No need of electric power
3. Capacity of the system drops
rapidly with lowered
evaporator pressure
Capacity of the system
decreases with the lowered
evaporative pressure, by
increasing the steam pressure
in generator.
4. At partial loads performance
is poor.
At partial loads performance is
not affected.
5. Mechanical energy is supplied
through compressor
Heat energy is utilised
6. Energy supplied is ¼ to ½ of Energy supplied is about one

36. S.No
.
Vapour Compression System Vapour Absorption System
7. Charging of the refrigerating
to the system is easy
Charging of refrigerant is
difficult
8. Preventive measure is needed,
since liquid refrigerant
accumulated in the cylinder
may damage to the cylinder
Liquid refrigerant has no bad
effect on the system.

37. Layout:
3

38. Air Conditioning
• It is the mechanism to maintain the atmosphere of an
enclosed space at a required temp, humidity and purity
• Air conditioning is the science which deals with the
supply and maintaining desirable internal atmospheric
condition irrespective of external condition.
• Refrigeration system is at heart of AC system
Types Used:
•Self-contained
•Refrigerant circulating
•Chill water circulating

39. Classification of Air Conditioning
A) According to purpose.
i) comfort air conditioning system
ii) Industrial air conditioning
B) According season of year.
i) Winter air conditioning
ii) Summer air conditioning
iii) Year round (All weather air conditioning)

40. Classification of Air Conditioning
C) According to equipment arrangement
i) central air conditioning
ii) unitary air conditioning
D) According to working substance used.
i) All air system
ii) chilled water system
iii) Air water system
E) According to general market requirements
i) Window air conditioning
ii) Split air conditioning

41. 4

42.  This is also called room air conditioner.
 This unit consists of the following.
1. A cooling system to cool and dehumidify the
air involves a condenser, a compressor and a
refrigerant coil.
2. A filter to any impurities in the air. The filter
is made of mesh, glass wool or fibre.
3. A fan and adjustable grills to circulate the air.
4. Controls to regulate the equipment
operation.

43.  The low pressure refrigerant vapour is
drawn from the evaporator to the hermetic
compressor through suction pipe.
 It is compressed from low pressure to the
high pressure and supplied to the
condenser.
 It is condensed in the condenser by
passing the outdoor air over the condenser
coil by a fan.
 The liquid refrigerant is passed through
the capillary into the evaporator.

44. 5. In the evaporator the liquid refrigerant picks
up the heat from the refrigerator surface
and gets vaporized.
6. A motor driven fan draws air from the room
through the air filter and this air is cooled
by losing its heat to the low temperature
refrigerant and cold air is circulated back
into the room.
7. The vapour refrigerant from the evaporator
goes to the compressor from evaporator and
the cycle is repeated.
8. Thus the room is air conditioned

45. 9. The quantity of air circulated can be
controlled by the dampers.
10. The moisture in the air passing over the
evaporator coil is dehumidified and drips
into the trays.
11. This water evaporator to certain extent and
thus helps in cooling the compressor and
condenser.
12. The unit automatically stops when the
required temperature is reached in the
room. This is accomplished by the
thermostat and control panel.

46. 5

47.  Construction
◦ A compressor
◦ An expansion valve
◦ A hot coil (on the outside)
◦ A chilled coil (on the inside)
◦ Two fans
◦ A control unit
Working of this system will be same as window type
a.c. system

48.  Image Refrences
 1- https://sp.yimg.com/ib/th?id=HN.608049691713736118&pid=15.1&P=0
 2-http://engin1000.pbworks.com/f/1299970370/absorption_refrigeration_diagram.jpg
 3- https://sp.yimg.com/ib/th?id=HN.607992044664326121&pid=15.1&P=0
 4-http://www.hometips.com/wp-content/uploads/2012/04/window-air-conditioner-diagram-
11.gif
 5-
https://www.growershouse.com/wordpress/wpcontent/uploads/2013/05/Mini_split_explanation_
diagram.jpeg
 Content References
 – Elements of Mechanical Engineering by H.G. Katariya, J.P Hadiya, S.M.Bhatt , Books India
Publication.
 -Elements of Mechanical Engineering by V.K.Manglik, PHI
 -Elements of Mechanical Engineering by R.K Rajput.
 -Elements of Mechanical Engineering by P.S.Desai & S.B.Soni

50. EXIT