This document provides an overview of refrigeration and air conditioning systems. It discusses the definition and necessity of refrigeration, as well as its major applications in food processing, chemical industries, and other special uses. It then describes the vapor compression refrigeration cycle and its components in detail. Other refrigeration cycles discussed include vapor absorption, air refrigeration (Bell Coleman cycle), and refrigeration systems used in aircrafts such as the bootstrap air cooling system. Key concepts like the unit of refrigeration, coefficient of performance, and the working of open and closed air systems are also summarized.

1. REFRIGERATION &
AIR CONDITIONING
S CHANDRA SEKHAR
Mechanical Dept.

2. Contents
INTRODUCTION TO REFRIGERATION:
Necessity and applications
Unit of refrigeration and C.O.P.
Mechanical refrigeration
Types of ideal cycles of refrigeration
Air refrigeration:
Bell coleman cycle
Open and dense air systems
Refrigeration systems used in air crafts and

3. REFRIGERATION
Refrigeration may be defined as a process of removing heat from a substance and
pumping it to the surroundings. It also includes the process of maintaining and reducing
the temperature of a body below the general temperature of its surroundings.

4. To understand the above definition, let us
consider an example from the daily life.
It is a well-known fact that the spoilage of food and many other items reduces at
a lower temperature.
At a lower temperature, molecular motion slows down and the growth of
bacteria that causes food spoilage also retards.
Thus to preserve many types of perishable food products for a longer duration,
we use refrigerators in our homes, canteens, hotels, etc.
The temperature of the food products has to maintained at a level below that of
surroundings.
For this we keep the food products in a refrigerator. The inside volume of the
refrigerator where we store food products or any other items is much less than
the volume of the room where the refrigerator is kept. The room in this case is
the surrounding environment.
Food products in the refrigerator initially were at a higher temperature than
desired temperature, meaning that it had some unwanted heat. If its heat is
removed, its temperature will decrease. The refrigerator removes unwanted heat
from the food products and throws away that heat to the room.

5. Necessity of Refrigeration
The fundamental reason for having a refrigerator is to keep food cold. Cold
temperatures help food stay fresh longer. The basic idea behind refrigeration is to
slow down the activity of bacteria (which all food contains) so that it takes
longer for the bacteria to spoil the food.
For example, bacteria will spoil milk in two or three hours if the milk is left out
on the kitchen counter at room temperature. However, by reducing the
temperature of the milk, it will stay fresh for a week or two -- the cold
temperature inside the refrigerator decreases the activity of the bacteria that
much. By freezing the milk you can stop the bacteria altogether, and the milk can
last for months

6. Applications
of
Refrigeratio
n
The applications of refrigeration can be grouped
into following three major equally important
areas:
 Food processing, preservation and
distribution.
 Chemical and process industries
 Special applications

7. Food processing, preservation and distribution:
Food preservation is one of the most important application of
refrigeration. It is well known that food products can be preserved for a
longer time, if stored them at lower temperatures. Both the live and
dead products can be preserved for longer time using refrigeration.
Live products stands for the products like fruits, vegetables and dead
products for the products like fish, chicken, meat etc.

8. Refrigeration in Chemical and Process Industries:
For removal of heat of reaction in various chemical industries.
 For dehumidification of process air in pharmaceutical industries.
 For recovery of solvents, storage of low boiling point liquids.

9. Special Applications of refrigeration:
 For storage of blood plasma, tissues, etc.
 For manufacture and storage of drugs.
 In surgery for local anesthesia.
 Desalination of water by freezing.
 Manufacture of ice, ice cubes, flakes, etc.
 For storage of vaccines, medicines in remote and rural areas.

10. Unit of Refrigeration:
The unit of refrigeration is expressed in terms of "Ton of Refrigeration" (TR).
One Ton of refrigeration: It can be defined as the amount of refrigeration effect
produced by the uniform melting of one ton of ice (1000 kg) from and at 0°C in 24
hrs.
1 TR = (335x1000)/ 24 KJ/hr. (where latent heat of ice= 335 KJ/Kg)
= 13958.333 KJ/hr.
= 13958.333/60 KJ/min
1 Tonne of refrigeration (TR)= 232.6 KJ/min

11. Coefficient of Performance of a Refrigerator:
•C.O.P =
𝑅𝑒𝑓𝑟𝑖𝑔𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑒𝑓𝑓𝑒𝑐𝑡
𝑤𝑜𝑟𝑘 𝑖𝑛𝑝𝑢𝑡
The performance of a refrigeration
system is expressed by a term known as
the coefficient of performance(C.O.P.)
Therefore the C.O.P is defined as the
ratio of refrigeration effect to the work
input.
C.O.P =
𝑹
𝒘

12. Mechanical
refrigeration:
Mechanical refrigeration, often referred to simply as
refrigeration, is a process by which heat is removed
from a location using a man-made heat-exchange
system.
This method is widely used to obtain desired
refrigeration. It works on the principle of reversed
cornot cycle.

13. Mechanical refrigeration can be
classified into various groups
such as,
1. Vapor compression refrigeration system
2. Vapor absorption refrigeration system
3. Air refrigeration system
4. Steam jet refrigeration system
5. Non-conventional refrigeration system

14. Vapour Compression
Refrigeration cycle
This is the widely used cycle as
compared to others…
The components of the Vapor
Compression Refrigeration cycle
are
 Compressor
 Condenser
 Receiver
 Expansion Valve &
 Evaporator.

15. The detailed
explanation
of the above
parts is as
follows.
1. Compressor:
The vapour at low pressure and low temperature enters the
compressor from the evaporator where it is compressed to high
pressure and high temperature.
This high pressure and temperature vapour refrigerant is
discharged into the condenser through the discharge valve.
2. Condenser:
The condenser or cooler consists of coils of pipe in which the
high pressure and temperature vapour refrigerant are cooled and
condensed.
The refrigerant while passing through the condenser gives up its
latent heat to the surroundings condensing medium which is
normally air or water.

16. 3. Receiver:
The condensed liquid refrigerant from the condenser is stored in a vessel known
as a receiver from where it is supplied to the evaporator through the expansion
valve.
4. Expansion Valve:
It is also called a throttle valve. Its function is to allow the liquid refrigerant
under high pressure and temperature to pass through it where it reduces its
temperature and pressure.
5. Evaporator:
It also consists of coils of pipe in which liquid-vapour refrigerant at low
pressure and temperature is evaporated and converted into vapour refrigerant at
low pressure and temperature.

17. Working of Vapor Compression Refrigeration System:
The working of Vapor Compression Refrigeration System can be completed under 4 processes and
are as follows.
Compression Process:
The vapour at low temperature and low pressure enter the compressor where it is compressed and
subsequently, its temperature and pressure considerably increase.
Condensation Process:
This vapour after leaving the compressor enters into the condenser, where it is condensed into high-
pressure liquid and is collected in a receiver tank.

18. Expansion Process:
From the receiver tank, it passes through the expansion valve, where it is throttled down to
low pressure and temperature.
Vaporization Process:
After finding its way through an expansion valve, it finally passes onto the evaporator,
where it extracts heat from the surroundings or circulating fluid and vaporizes to lower
pressure vapour.
Note:
• Work is done by the compressor.
• The heat extracted from the evaporator is the difference of heat entering the evaporator
and heat leaving the evaporator.

19. Advantages:
The temperature at the evaporator
section can be controlled employing
regulation of expansion valve.
It exhibits high Coefficient of
Performance.
The running cost is low because the
volume circulation of the refrigerant is
low in the system.

20. Disadvantages:
Make sure that there should be no
leakage of refrigerant from the
pipes/hose.
Refrigerant can affect the atmosphere.
The cost of the system is high.

21. Vapor Absorption Refrigeration Cycle:
In the Vapor Absorption process, the compression process of the vapor compression cycle is
replaced by an absorber, a generator, and a pump.
The principle of the system is to make use of two substances that can be separated when
heated.
The two substances can be
1.Ammonia (Refrigerant) and
2.Water (Absorbent).

23. Components
of Vapor
Absorption
Refrigeration
Cycle:
The components of Vapour Absorption Refrigeration
Cycle are as follows.
• Condenser
• Expansion Valve
• Evaporator
• Absorber
• Pump
• Generator

24. Working of Vapor Absorption Refrigeration Cycle:
In this type of refrigeration system, the vapor produced in the evaporator passes into the
absorber.
The absorber consists of a homogeneous mixture of ammonia and water known as aqua
ammonia. In the absorber, the vapor is absorbed and released from the absorbent, which
maintains constant low pressure.
• This process takes place at a temperature slightly above that of the surroundings.
• In this process, some heat is transferred to the surroundings. The strong ammonia solution
is then pumped through a heat exchanger to the generator by a pump where high pressure
and temperature are maintained.

25. • The ammonia vapor enters into the condenser where it gets condensed into liquid
ammonia.
• The liquid ammonia which is at high pressure is passed through an expansion
valve through which wet Ammonia vapor, at low temperature and pressure, comes
out.
• The vapor is then passed through the evaporator. The evaporator absorbs heat and
is dried. The dried vapor is again taken to the absorber and thus the cycle is
completed.

26. Air refrigeration or
bell coleman
refrigeration system
(i) Open cycle
(ii) Closed or dense air
cycle.

27. Bell Coleman Cycle
The Bell Coleman Cycle is a refrigeration cycle where the working fluid is air which
is compressed and expanded but do not change state.
This cycle is the modification of reverse Carnot cycle.

29. The above figure shows the different processes in a Bell Coleman Cycle.
Bell Coleman Cycle consists of a compressor, cooler, expander and
refrigerator. In this cycle, the process of compression and expansion of gas
is isentropic and heat absorption and rejection of heat takes place at
constant pressure i.e isobaric process.

30. PV and TS diagrams of
Bell Coleman Cycle
The figure shows PV and TS
diagrams of Bell Coleman
Cycle . Here P1 , V1 , T1, S1
represents volume, pressure
,temperature and entropy
respectively at point 1 and so
on.

31. Below is the
elaboration of
four steps of
Bell Coleman
Cycle :-
i) 1-2 : Isentropic Compression :-
This is the first step of Bell Coleman Cycle. In this step, air
is drawn from refrigerator to compressor cylinder where it
is compressed isentropically. No heat is transferred during
this process. As the air is compressed, the volume
decreases from V1 to V2 ,pressure increases from P1 to P2
and temperature increases T1 to T2 but entropy remains
constant as no heat is transferred.
ii) 2-3 : Adiabatic Cooling process :-
After Isentropic compression, the warm air is passed through
cooler where it is cooled adiabatically i.e at constant
pressure. This cooler can be an air cooled or water cooled
cooler. In most of the cases water cooled cooler is used. In
this cooling process, pressure will remain contsant but
temperature will decrease, volume will decrease and entropy
will also decrease.

32. iii) 3-4 : Isentropic Expansion :-
In this step , the cooled air is expanded isentropically. Since air is expanded,
therefore volume will increase and pressure will decrease.
As this process is isentropic entropy will remain constant and temperature
will decrease.
iv) 4-1 : Adiabatic Refrigeration :-
It is the last step of Bell Coleman Cycle. In this step the cooled and expanded
air absorbs heat from the refrigerator. Heat is transferred from refrigerator to
air. In this process, the air expands due to heat from volume V4 to V1 ,
temperature increases from T4 to T1 and entropy will also increase from S4 to
S1.

33. Equation of Coefficient of performance (COP) of Bell Coleman
cycle
Heat absorbed during cycle per kg of air q4-1 = Cp(T1-T4)
Heat rejected during cycle per kg of air q2-3 = Cp(T2-T3)
Then the work done per kg of air during the cycle is = Heat rejected –
Heat absorbed
= Cp(T2-T3) - Cp(T1-T4)
Coefficient of performance:

34. Advantages
• Air is non-flammable, so there is no chance of fire
hazards.
• Air is cheaply and easily available as compared to other
refrigerants
• The weight of air refrigeration system per ton of
refrigeration is much less as compared to other systems.
Because of this reason, this system is employed in
aircraft applications. weight is an important consideration
in aircrafts.

35. Dis advantages
The COP of the system is very low
as compared to other systems.
The amount of air required to be
circulated for producing cold effect
is more as compared to other
refrigerants used in other systems.

36. Open air system:
The Figure shows a flow diagram of the open air system. Here air is discharged into cold
chamber at atmospheric pressure and allowed to come in direct contact with the cold body.
The compressor draws the air from the atmosphere, compresses it, and delivers it to the
cooler.
As air flows through the cooler, heat is removed from it causing a great decrease in its
volume. In the ideal case, the pressure remains constant during cooling; in the actual case
there is slight pressure drop.

37. The expansion of air is carried
out in the expansion cylinder.
The low temperature air
leaving the expansion cylinder
then enters the cold chamber
and abstracts heat from the
bodies kept in the chamber and
in turn lowers temperature in
the cold chambers.

38. Figure shows theoretical combined
P-V diagram for both the
compressor and expander (air
motor).
• 1- 2 Isentropic compression
• 2- 3 Constant pressure heat-rejection
• 3- 4 Isentropic expansion in expander
• 4- 1 Constant pressure heat-addition

39. Closed or Dence air
system:
The basic air standard cycle is
shown in Fig. 36.15. Air is
contained in the system and is
compressed from B by a
reciprocating or rotory
compressor. The compressed
air at C is passed on to the air
cooler where it cools down at
constant pressure, to stare D.

40. The high pressure gas at D is then
passed on to an expansion cylinder.
Here the air expands upto A, delivers
work and gets cooled. The work
delivered may be fed back to the
compressor by mounting the
compressor and the expander on the
same shaft. The cooler air at A is
passed through the refrigerator. The
heat picked up by the air in the
refrigerator causes its state to change to
point B and the cycle repeats.
The cycle discussed above is known as
closed or dense air system. And the P-
V and T-S diagrams will be same as for
open cycle

41. Refrigeration systems
used in aircraft:
 Simple air cooling system
 Simple air evaporative cooling system
 Boot strap air cooling system
 Reduced ambient air cooling system
 Regenerative air cooling system.

42. Bootstrap
Air
refrigeration
system:
Boot strap refrigeration or Air refrigeration cycle is a
refrigeration cycle that use air as a working fluid and
is often incurred in the Aircrafts.
The figure provided below represents bootstrap air
cooling system. it is actually a modification of simple
aircraft refrigeration system. It consists of two heat
exchanger and a secondary compressor. The heat of
compression is released by using two heat exchanger
in bootstrap system and air is compressed three
times.

45. • It has two heat exchangers instead of one and a cooling turbine drives a
secondary compressor. The air bled from the main compressor is first
cooled by the ram air in the first heat exchanger.
• The air is compressed to a higher pressure and temperature in the
compressor of the cooling turbine.
• A substantial amount of heat of compression is removed in the secondary
heat exchanger and the air is cooled further as its expands through the
turbine section of the cooling turbine.

47. DIS-ADVANTAGES
• Lower COP. Bootstrap system use air as the refrigerant. ...
• Large Sized Components. Despite low weight per ton, air
refrigeration system has large-sized components to control the
flow of air.
• Frosting Due to High Moisture Content. The moisture in air
could freeze the lines of the system. ..

48. THANK YOU