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1. 5022-REFRIGERATION
& AIR CONDITIONING
MODULE-1

3. Refrigeration
DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE
OF POLYTECHNICS,
PERUMBAVOOR
It is defined as the process of providing and
maintaining a temperature well below that of
surrounding atmosphere.
In other words refrigeration is the process of cooling
substance.
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4. Refrigerating Effect: 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
.
DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
POLYTECHNICS, PERUMBAVOOR
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5. CAPACITY OF REFRIGERATION / UNIT OF
REFRIGERATION:
Capacity of a refrigerating machinesare expressed by their
cooling capacity.
The standard unit used for expressing the capacity of refrigerating
machine is tonof refrigeration. (TR)
One ton of refrigeration is defined as, “the quantity of heat
removed (refrigerating effect produced) to freeze one ton ofwater
into ice in a duration of 24 hours at 0o c”.
Atonof refrigeration (TR)isalsodefined asthe amount of refrigeration effect
produced (Heatliberated)duringtheuniformmelting of one ton of ice from and
at0o c in24 hours
DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
POLYTECHNICS, PERUMBAVOOR 5

6. Heat extracted from water during freezing at 00C = Latent heat of ice
Latent heat of ice =336 kj/kgk
ie.) 336kj heat is to be removed from 1 kg of water at 00C to convert it into 1kg of
ice.
1 Ton=2000 Pound =907.18kg (Ton used here is short ton which is an American
unit)
Therefore 1 Ton of Refrigeration=1TR=Amount of heat extracted from 1
ton(907.18kg) of water at 00C to freeze it into ice at 00C in 24 hours
DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
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7. Oneton of Refrigeration
For calculation purpose,
One ton of refrigeration = 12600 kJ/hr
= 210kJ/min
= 3.5 kJ/s
DEPARTMENT OF MECHANICAL ENGINEERING, SCMS
COLLEGE OF POLYTECHNICS, PERUMBAVOOR
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8. HEAT ENGINES
The devices that convert heat to
work.
1. They receive heat from a high-
temperature source (solar energy,
oil furnace, nuclear reactor, etc.).
2. They convert part of this heat to
work (usually in the form of a
rotating shaft.)
3. They reject the remaining waste
heat to a low-temperature sink
(the atmosphere, rivers, etc.).
4. They operate on a cycle.
Heat engines and other cyclic
devices usually involve a fluid to
and from which heat is
transferred while undergoing a
cycle. This fluid is called the
working fluid.
Part of the heat
received by a heat
engine is converted to
work, while the rest is
rejected to a sink.
DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE
OF POLYTECHNICS, PERUMBAVOOR
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9. The thermal efficiency is the index of performance of a work-producing device
or a heat engine and is defined by the ratio of the net work output (the desired
result) to the heat input (the costs to obtain the desired result).
For a heat engine the desired result is the net work done and the input is the
heat supplied to make the cycle operate. The thermal efficiency is always less
than 100 percent
THERMAL EFFICIENCY th
th 
Desired Result
Required Input
OUT PUT
DEPARTMENT
OF
MECHANICAL
ENGINEERING,
SCMS
COLLEGE
OF
POLYTECHNICS,
PERUMBAVOOR
9

10. The cycle thermal efficiency may be written as
THERMAL EFFICIENCY (CONT..)
th
net out
in
in out
in
out
in
W
Q
Q Q
Q
Q
Q



 
,
1
Cyclic devices such as heat
engines, refrigerators, and
heat pumps often operate
between a high-temperature
reservoir at temperature TH
and a low-temperature
reservoir at temperature TL.
th
L
H
Q
Q
 
1
DEPARTMENT
OF
MECHANICAL
ENGINEERING,
SCMS
COLLEGE
OF
POLYTECHNICS,
PERUMBAVOOR
10

11. Refrigerator
Refrigerator:
A refrigerator is a reversed heat
engine which cools and
maintains the temperature of a
body lower than the
atmospheric temperature.
In refrigerator heat is transferred from lower
temperature body to a higher temperature
body by applying some external work
The main objective of refrigerator is to keep
the lower temperature body below the
surrounding temperature by removing heat QL
from the colder body.
DEPARTMENT
OF
MECHANICAL
ENGINEERING,
SCMS
COLLEGE
OF
POLYTECHNICS,
PERUMBAVOOR
11

12. HEAT PUMP
• Heat pump is similar to refrigerator
• The working principle is same
• Here also heat is transferred from lower
temperature body to a higher
temperature body by applying some
external work
• The only difference is in the working
temperature
The objective of a heat pump is to supply
heat QH into the warmer space
DEPARTMENT
OF
MECHANICAL
ENGINEERING,
SCMS
COLLEGE
OF
POLYTECHNICS,
PERUMBAVOOR
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13. DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE OF POLYTECHNICS, PERUMBAVOOR 13

14. Co efficient of Performance (COP)
It is defined as the ratio of heat extracted in a given
time (refrigerating effect) to the workinput.
Co efficient of performance = Heat extracted
Work Input
Co efficient of performance = Refrigerating Effect
Work Input
Co efficient of performance = N
W
.
DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
POLYTECHNICS, PERUMBAVOOR
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15. DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
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16. DEPARTMENT OF MECHANICAL ENGINEERING, SCMS
COLLEGE OF POLYTECHNICS, PERUMBAVOOR
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17. DEPARTMENT OF MECHANICAL ENGINEERING, SCMS
COLLEGE OF POLYTECHNICS, PERUMBAVOOR
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18. ICE-REFRIGERATION
DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE OF POLYTECHNICS,
PERUMBAVOOR
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19. DRY ICE-REFRIGERATION
DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE OF POLYTECHNICS, PERUMBAVOOR
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20. STEAM JET REFRIGERATION SYSTEM/ THROTTLING
REFRIGERATION SYSTEM
DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE OF POLYTECHNICS, PERUMBAVOOR
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21. • The boiling temp. of water depends on its pressure
• Water boils at 1000 C at atmospheric pressure
• If we reduce the pressure it will boil at low temp.
• At pressure near vacuum it will even boil at 4 to 5 C
• This principle is adopted in steam jet water refrigeration system
• The pressure on the surface of a flash chamber is reduced by steam jet and ejector
system
• The steam passing through the nozzle and ejector acquires high velocity and sweep the
vapours and gases present above the surface of water in the flash chamber
• It produces low pressure or high vacuum on the surface of the water in the flash
chamber , causes it to evaporate at low temp.
• At this lower pressure some of the water sprayed to the flash chamber gets evaporated.
• For the water to be evaporated it requires latent heat this heat will be taken from the
water present in the flash chamber
• Hence the remaining water in the flash chamber gets cooled.
DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE OF POLYTECHNICS, PERUMBAVOOR 21

22. DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
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23. Air Refrigeration System
One of the earliest method.
Obsolete due to low COP and high operating cost.
Preferred in Aircraft Refrigeration due to its low weight.
Characteristic :
- Throughout the cycle, Refrigerant remains in gaseous state.
Air Refrigeration
Closed System Open System
• Air refrigerant contained within
piping or components of
system.
• Pressures above atm. Pr.
• Refrigerator space is actual room to be
cooled.
• Air expansion to atm. Pr. And then
compressed to cooler pressure.
DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE OF POLYTECHNICS, PERUMBAVOOR 23

24. DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE OF POLYTECHNICS, PERUMBAVOOR 24

25. Air Refrigeration System
DEPARTMENT
OF
MECHANICAL
ENGINEERING,
SCMS
COLLEGE
OF
POLYTECHNICS,
PERUMBAVOOR
Closed System Vs. Open System :
1. Suction to compressor in Closed System may be at high pressures.
Hence, the size of Expander and Compressor can be kept small.
2. In Open Systems, air picks up the moisture from refrigeration chamber. This
moisture freezes and chokes the valves.
3. Expansion in Open System is limited to atm. Pr. Level only. No such
restriction to Closed System.
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ENGINEERING, SCMS COLLEGE OF
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ENGINEERING, SCMS COLLEGE OF
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28. DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
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29. Air Refrigeration System working on Reverse Carnot Cycle
3
2
4
Isotherms
Reversible
Adiabatic or
Isentropic
T2
Expansion
Compression
1
T1
Pressure
Volume
P –V Diagram
3 2
1
4
T1
Expansion Compression
T2
Temperature
Entropy
1’
DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE OF POLYTECHNICS, PERUMBAVOOR
4’
T –s Diagram
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30. 2
1
4
T1
Expansion Compression
T
3
2
Temperature
Entropy
1’
4’
Operation :
1 – 2 :ReversibleAdiabatic
Compression Or Isentropic
Compression. Requires
external power. Temp. rises
from T1 to T2. and Pressure
rises from P1 to P2
2 – 3 : Isothermal Compression.
Heat Rejection to Hot Body at const.
Temp.
Pressure increases from P2 to P3. The
heat rejected by the air during the
process=T2(S2-S3)
.
Reverse Carnot Cycle
DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
30

31. 2
1
4
T1
Expansion Compression
T
3
2
Temperature
Entropy
1’
4’
Operation :
3 – 4 : Reversible Adiabatic Expansion or
Isentropic Expansion.
Temp. falls from T3 to T4.
Pressure reduces from P3 to P4.
No heat is absorbed or rejected during
this process
4 – 1 : Isothermal Expansion.
Heat Extraction from Cold
Body(Refrigerated Space). This process
is carried out at constant temp.
Pressure reduces from P4 to P1
The heat absorbed by the air during the
process=T1(S1-S4)
=T1(S2-S3)
Reverse Carnot Cycle
DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
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32. 3 2
1
4
T1
Expansion Compression
T2
Temperature
Entropy
1’
4’
Heat extracted from cold Body : =T1 (S1-S4)
=T1 (S2-S3)
Heat rejected to the hot Body = T2 (S2-S3)
Work done per cycle = Heat rejected-Heat extracted
= T2 (S2-S3)- T1 (S2-S3)
Work Done
T2 T1

(T2 - T1 ) (S2-S3)

T2 (S2-S3)- T1 (S2-S3) T1

T1 (S2-S3)
COP 
Heat Extracted
Reverse Carnot Cycle
T1 (S2-S3)
T1

TL
THTL
DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
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ENGINEERING, SCMS COLLEGE OF
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ENGINEERING, SCMS COLLEGE OF
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ENGINEERING, SCMS COLLEGE OF
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ENGINEERING, SCMS COLLEGE OF
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ENGINEERING, SCMS COLLEGE OF
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ENGINEERING, SCMS COLLEGE OF
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42. Bell – Coleman / Reverse Brayton
Cycle/Reversed Joule Cycle
Elements of this system :
1. Compressor.
2. Heat Exchanger.
3. Expander.
4. Refrigerator.
Work gained from Expander is used
to drive Compressor.
Hence, less external work is
required.
Heat Exchanger
Cooling
Water
Refrigerator
Compressor
Expander
Cold Air
Very Cold Air
Warm Air
DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
POLYTECHNICS, PERUMBAVOOR
Hot Air
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43. Bell – Coleman / Reverse Brayton
Cycle/Reversed Joule Cycle
3 2
1
4
Isobars
Adiabatic
Expansion
Compression
Pressure
Volume
P –V Diagram
3
2
1
4
Expansion
Compression
Temperature
Entropy
Isobars
DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
POLYTECHNICS, PERUMBAVOOR
Adiabatic
T –s Diagram
43

44. Bell – Coleman / Reverse Brayton Cycle
/Reversed Joule Cycle
3
2
1
4
Expansion
Compression
Temperature
Entropy
Isobars
Adiabatic
1 – 2 :ReversibleAdiabatic
Compression Or Isentropic
Compression. Requires
external power. Temp. rises
from T1 to T2. and Pressure rises
from P1 to P2
2 – 3 : Constant Pressure / isobaric Heat
rejection.
Heat Rejection to Hot Body at const.
Pressure. Temp. reduces from T2 to T3.
.
Heat Rejected in Heat Exchanger :
Qrejected  m CP (T2 T3)
DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE OF POLYTECHNICS, PERUMBAVOOR 44

45. Bell – Coleman / Reverse Brayton Cycle
/Reversed Joule Cycle
3
2
1
4
Expansion
Compression
Temperature
Entropy
Isobars
Adiabatic
3 – 4 : Reversible Adiabatic Expansion or
Isentropic Expansion.
Temp. falls from T3 to T4.
Pressure reduces from P3 to P4.
No heat is absorbed or rejected during
this process
4 – 1 : Constant Pressure / isobaricHeat
addition.
Heat Extraction from Cold
Body(Refrigerated Space). This process
is carried out at constant pressure.
Temp. increases from T4 to T1
Heat Absorbed in Refrigerator :
Qadded  m CP (T1 T4 )
DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE OF POLYTECHNICS, PERUMBAVOOR 45

46. COP OF Bell-Coleman Cycle
Heat Absorbed in Refrigerator :
Work input during the cycle, W= Heat rejected - Heat absorbed
= mCp (T2 - T3) - mCp (T1 - T4)
C.O.P = T4(T1
DEPARTMENT OF MECHANICAL
ENGINEERING, SCMS COLLEGE OF
46
Qadded  m CP (T1 T4 )
Heat Rejected in Heat Exchanger :Qrejected  m CP (T2 T3)
Taking T4 outside

47. DEPARTMENT OF MECHANICAL ENGINEERING, SCMS COLLEGE
OF POLYTECHNICS, PERUMBAVOOR
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ENGINEERING, SCMS COLLEGE OF
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ENGINEERING, SCMS COLLEGE OF
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ENGINEERING, SCMS COLLEGE OF
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OF POLYTECHNICS, PERUMBAVOOR