Unit 5 REFRIGERATION AND AIR CONDITIONING

1. ME8595 – THERMAL ENGINEERING- II
UNIT-5
REFRIGERATION AND
AIR CONDITIONING
PREPARED BY
R. Prakash,
Assistant Professor,
Department of Mechanical Engineering,
Kongunadu College of Engineering and Technology

2. REFRIGERATION
 It is the process of removing heat
continuously from a body/object, to reduce its
temperature lower than that of its
surrounding atmospheric and maintaining it
by continuously absorbing the heat

3. REFRIGERATOR
It is an equipment used for producing
and maintaining the temperature in a
closed space below the surrounding
atmospheric temperature

4. REFRIGERANT
• Ammonia (NH3)
• Carbon dioxide (CO2)
• Sulphur dioxide (SO2)
• Freon which has the types of R-11, R-12, R-21,
R-22 and R-502

5. REFRIGERANT
 Refrigerant is a fluid which absorbs the heat from the
body and rejects the heat at high temperature
 Properties of refrigerant :
It should have low freezing and low boiling point
It should have high co-efficient of performance
It should be non-Explosive
It should have low specific heat of liquid
It should be non flammable
It should be non corrosive to metal

6. APPLICATIONS OF REFRIGERATION
• For preserving the food, fruits, and drinks for a
long duration
• For preserving the flowers, medicines and
medical drugs
• Refrigeration is used in refineries for removing
wax

8. TERMINOLOGY OF REFRIGERATION
• Refrigeration Effect :
– Refrigeration effect 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

9. Capacity of refrigeration unit
• The capacity of refrigerating machines are expressed by
their cooling capacity
• The standard unit used for expressing the capacity of
refrigerating machines is tonne of refrigeration
• One tonne of refrigeration is defined as the quantity of
heat abstracted ( refrigerating effect ) to freeze ( into
ice ) one tonne of water in a duration of 24 hours at 0oC

10. 1 tonne of refrigeration = 210 KJ/Min
= 3.5 KJ/s
= 3.5 KW

11. Co- Efficient of Performance (COP)
• Performance of a refrigeration system is
measured by Co-efficient of performance
(COP)
• It is defined as the ratio of heat extracted in a
given time ( refrigerating Effect ) to the work
input
• COP = Heat Extracted / work done

12. Classifications of refrigerants
• Primary refrigerants
• Secondary refrigerants

13. Primary refrigerants
• These are refrigerants that directly take
part in the refrigeration system
• R-12 - Dichloro difluoro methane - CCl2F2
• R-22 - Monochloro difluoro methane - CHClF2
• R-717 - Ammonia - NH3
• R-744 - Carbon dioxide - CO2

14. Secondary refrigerants
• These are the refrigerants which are first
cooled by primary refrigerants and then used
for cooling purpose
• Calcium chloride - CaCl2
• Sodium chloride - NaCl
• Glycols

15. Types of refrigerators
• Vapour compression refrigerators
• Vapour absorption refrigerators

16. Vapour compression refrigerators
Main Parts :
–Compressor
–Condenser
–Receiver
–Expansion Valve
–Evaporator

17. Vapour compression refrigerators
High T,
Low P, Vapour
High T,
High P, Vapour
Low T,
High P,
Liquid
Low T,
Low P,
Liquid
Heat absorbs
Heat rejects

18. Vapour absorption refrigerators
Main Parts :
• Absorber
• Pump
• Heat Exchanger
• Generator
• Condenser
• Expansion valve
• Evaporator

19. Vapour absorption refrigerators
H.E

22. Ammonia-water vapour absorption
refrigeration system
• The working of ammonia-water absorption
refrigeration system is based on the simple
vapor absorption refrigeration system. In this
system ammonia is used as the refrigerant and
water is used as the absorbent. The ammonia-
water absorption system is used in the
domestic as well the commercial applications
where the requirement of the temperature is
above 32 degree F.

25. In a water-lithium bromide vapor absorption
refrigeration system, water is used as the
refrigerant while lithium bromide (Li Br) is used as
the absorbent.
In the absorber, the lithium bromide absorbs the
water refrigerant, creating a solution of water
and lithium bromide.
This solution is pumped by the pump to the
generator where the solution is heated.
The water refrigerant gets vaporized and moves
to the condenser where it is cooled while the
lithium bromide flows back to the absorber
where it further absorbs water coming from the
evaporator.

27. Layout of typical domestic
refrigerator

30. Comparison between Vapour compression & Vapour
Absorption refrigeration systems
S.No Vapour Compression System Vapour Absorption System
1 The system has more wear and tear and produces noise
due to the moving parts in the compressor
The only moving part is the pump. The system is
quiet in operation and is subjected to very little
wear
2 A compressor ( Mechanical energy ) is used to change the
condition of the refrigerant from the evaporator
Heat energy is used to change the condition of the
refrigerant from the evaporator
3 The refrigerant capacity for a compressor unit is less than
1000 tonnes
Refrigerants with more than 1000 tonnes capacity
can be built
4 Electric power is needed to drive the system . i.e to run
the compressor
Heating coils or gas flame or even waste exhaust
steam can be used to heat the generator. Thus this
system can run even without electricity
5 Capacity of the system drops rapidly with lowered
evaporator pressure
Capacity of the system decreases very little with
lowered evaporator pressure
6 Energy supplied is ¼ to ½ of refrigerating effect Energy supplied is about 1 ½ times the
refrigerating effect
7 Refrigerant refilling is simple Refrigerating refilling is hard
8 At partial loads, the performance is poor At partial loads, the performance is not affected

31. AIR CONDITIONING

32. AIR CONDITIONING
• Air conditioning is the process of conditioning
the air according to the human comfort,
irrespective of external conditions

33. PSYCHROMETRY
• Science which is the study about the
behaviour of moisture air.

34. PROPERTIES OF PYSCHROMETRIC
• Atmospheric air:
Air in the atmosphere is referred to as
atmospheric air.
• Dry air:
The normal atmospheric air with out the
presence of water vapour is called dry air.
• Water vapour:
It is the moisture present in the dry air.

35. • Moisture:
It is the water vapour present in dry air.
• Moisture air:
It is the mixture of dry air and water vapour.
• Saturated air:
When the mixture of air and water vapour
at a given temperature contains the maximum
amount of water vapour that it hold then it is
known as saturated air.
• Humidity:
It is the mass of water vapour present in 1
Kg of dry air and is generally expressed in
terms of gm per kg of dry air.

36. • Absolute Humidity:
It is the mass of water vapour present in
1m cube of dry air and is generally expressed
in terms of gm per cubic meter of dry air.
• Relative humidity:
It is the ratio of actual mass of water
vapour in a given volume of moisture air to
the mass of water vapour in the same volume
of saturated air. at the same temperature and
pressure.

37. • Degree of saturation:
It is the ratio of actual mass of water
vapour in unit mass of dry air to mass water
vapour in the same volume of saturated air at
the same temperature.
• Dry Bulb Temperature (DBT):
The temperature which is measured by an
ordinary thermometer is known as dry bulb
temperature.

38. • Wet bulb temperature (WBT):
It is the temperature of air measured by a
thermometer when its bulb is covered with wet
cloth and is exposed to a current rapidly moving
air.
• Wet bulb depression (WBD):
It is the difference between dry bulb
temperature and wet bulb temperature.
• Dew point temperature (DPT):
It is temperature at which the water vapour
present in the air begins to condense when the
air is cooled.

39. • Dew point Depression (DPD):
It is the difference between dry bulb
temperature and dew point temperature.
• Psychrometer:
It is a device which is used for measuring
dry bulb and wet bulb temperature
simultaneously.

40. PSYCHROMETRIC PROCESS
• Sensible heating process
• Sensible cooling process
• Humidification process
• Dehumidification process

41. • Sensible heating process:
The heating of air with out addition of
moisture is known as sensible heating. The
heating is done by passing the air over heating
coil of tubes.
• Sensible cooling process:
The cooling of air with out removal of
moisture is known as sensible cooling. The
cooling is done by passing the air over cooling
coil of tubes.

42. • Humidification process:
The addition of water vapour to the air is
known as humidification. Humidification is
done by spraying water over air stream at
constant dry bulb temperature of air.
• Dehumidification process:
The removal of water vapour from the air
is known as dehumidification. The water
vapour from the air can be removed
chemically, physically or thermodynamically.

43. Requirements of comfort air
conditioning
• The following factors are affecting the human
comfort in air conditioning
• Temperature of air
• Humidity of air
• Air motion
• Air purity
• noise

44. Classifications of Air conditioning
• According to the purpose
– Comfort air conditioning
– Industrial air conditioning
• According to season of the year
– Summer air conditioning
– Winter air conditioning
– Year round air conditioning

45. Types of air conditioning
• Room air conditioning
• Window air conditioning
• Central air conditioning

46. Functions of air conditioning
• Cleaning air
• Controlling the temperature of air
• Controlling the moisture content
• Circulating the air

47. Window air conditioner
• Or Room air conditioner
• Refrigerant used : R-12 or R-22
• It consists of :
– Compressor
– Air cooled condensor
– Capillary tube
– Evaporator

49. • Condensor
– Refrigerant vapour ----- liquid Refrigerant
( High P, High T ) ( High P, Low T )
Capillary tube :
- Liquid Refrigerant------ Liquid Refrigerant
( High P, low T ) ( Low P, Low T )
Evaporator :
Liquid Refrigerant ------ vapour Refrigerant
( Low P, low T ) ( Low P, Low T)
Compressor:
Refrigerant vapour - ----- Refrigerant vapour
( low P, Low T ) ( High P, High T )

50. Split type room air conditioner
• They are used for small rooms and halls,
usually in places where window air
conditioners cannot be installed.
• It can be classified into two parts :
– The outdoor unit
– The indoor unit

51. Outdoor unit
• The outdoor unit, fitted outside the room,
houses components like the compressor ,
condenser, and expansion valve

52. • It consists of :
• Compressor :
– main component of the system
– used to compress the refrigerant
• Condenser coil :
 used to reject the heat from the refrigerant to the
outside air
• Condenser fan :
 rejecting the heat from the indoor unit to the space
outside the building
• Condenser motor :
 usually has two to three speeds. Smaller unit may
only have 1 speed of control and turns on/off
simultaneously with the compressor

53. Indoor unit
• The indoor unit comprises the evaporator or
cooling coil and the cooling fan. The spilt air
conditioner can be used to cool one or two
rooms

54. • It consists of
• Evaporator coil
• Control panel
• Air filter
• Supply and return Air Grills
• Fan Blower
• Capillary tube

57. Multispilt Air conditioner
• In units for one outdoor unit there are two
indoor units which can be placed in two
different rooms or at two different locations
inside a large room

59. HUMAN EFFORT USING AIR
CONDITIONING SYSTEM

68. COOLING TOWERS
• A cooling tower is a heat rejection device that
rejects waste heat to the atmosphere through
the cooling of a water stream to a lower
temperature.
• Cooling towers may either use
the evaporation of water to remove process
heat and cool the working fluid

69. TYPES OF COOLING TOWERS
There are two types.
• Wet type
• Dry type
Wet type
1. Atmospheric or natural draught cooling
tower (Natural draught)
2. Mechanical draught cooling towers

70. Atmospheric or natural draught cooling
tower (Natural draught)
1. Natural draught spray filled tower
2. Natural draught packed type tower
3. Hyperbolic cooling tower

73. Mechanical or Forced Draught
Cooling Tower

75. Dry cooling towers
• Direct type
• Indirect type

82. THANK
YOU