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Mechanical Engineering > Refrigeration and Air Conditioning > Flashcards

Refrigeration and Air Conditioning Flashcards

1
Q

What are refrigerants primarily classified into ?

A

Primary and Secondary Refrigerants

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2
Q

What is a primary refrigerant ?

A

It directly takes part in the refrigeration system

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3
Q

What is a secondary refrigerant ?

A

It is first cooled and then used

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4
Q

What is used to cool a secondary refrigerant ?

A

A primary refrigerant

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5
Q

What are primary refrigerants classified into ?

A

Halocarbon
Azeotrope
Inorganic
Hydrocarbon

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6
Q

What are the three types of properties refrigerants are checked for before use ?

A

Physical, Chemical and Thermodynamic

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7
Q

Why should a refrigerant have a low boiling point at atmospheric pressure ?

A

It provides for lower refrigeration temperature

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8
Q

How low should it be, generally ?

A

Lower than the required refrigeration temperature

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9
Q

What should be the condensing pressure of a refrigerant at normal temperature ?

A

Low

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10
Q

Why should a refrigerant have high critical temperature ?

A

Easy to provide refrigeration, even at room temperature

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11
Q

What is critical temperature ?

A

the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied.

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12
Q

Why should refrigerants have low freezing point ?

A

Easy to circulate even at room temperature

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13
Q

What kind of a coefficient of performance (COP), is desired (high or low) ?

A

High

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14
Q

What is coefficient of performance (COP) ?

A

Ratio of refrigeration effect to work input

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15
Q

What is a desirable horsepower/ ton of refrigeration ?

A

Low

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16
Q

What is ton of refrigeration ?

A

Amount of ice melted in 24 hours from 0 degree centigrade water

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17
Q

What is the required flammability of a refrigerant ?

A

Low flammability

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18
Q

Why should refrigerants have low water dissolvity ?

A

Reduces moisture chocking of expansion devices with narrow passages

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19
Q

What affect should refrigerants have on metals ?

A

They should be non corrosive to metals

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20
Q

How should refrigerants mix with lubricating oil ?

A

Should mix well

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21
Q

What kind of a dielectric strength in required for a refrigerant ?

A

Strong dielectric strength, especially for hermetically sealed units

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22
Q

What is the property of a hermetic seal ?

A

It is air tight

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23
Q

Why should refrigerants have high thermal conductivity ?

A

It increases heat transfer rates

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24
Q

What is the desired viscosity of a refrigerant ?

A

Low viscosity

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25
Q

What should be the thermal capacity of a refrigerant at evaporating temperature ?

A

High thermal capacity at evaporating temperature

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26
Q

What should be the thermal capacity of a refrigerant at condensing temperature ?

A

Low thermal capacity at condensing temperature

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27
Q

What is thermal capacity ?

A

Measurable physical quantity equal to the ratio of the heat added to (or removed from) an object to the resulting temperature change

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28
Q

What are some common refrigeration systems ?

A

Vapour Compression
Vapour Absorption
Air Refrigeration

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29
Q

What are some special refrigeration systems ?

A

Thermoelectric Refrigeration
Steam Jet Refrigeration
Vortex tube Refrigeration
Passive Refrigeration

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30
Q

What are the four main parts of a vapour compression refrigeration system ?

A

Compressor
Condensor
Expansion Device
Evaporator

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31
Q

What is the main function of a compressor ?

A

To suck vapours

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32
Q

What does a compressor do after sucking in vapours ?

A

It increases the pressure

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33
Q

Where do the vapours come to the compressor from ?

A

Evaporator

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34
Q

What happens to the vapours after the pressure is increased ?

A

Easily condensed at higher temperatures

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35
Q

What happens when the vapours are compressed ?

A

A large amount of heat is extracted

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36
Q

What is the main function of a condensor ?

A

To provide a heat transfer area

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37
Q

What does a condensor provide a heat transfer area to ?

A

Hot vapours

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38
Q

How do the vapours become liquid ?

A

Due to their high pressure

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39
Q

On what principle do they lose heat ?

A

Second law of thermodynamics

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40
Q

What is the second law of thermodynamics ?

A

Every natural thermodynamic process proceeds in the sense in which the sum of the entropies of all bodies taking part in the process is increased.

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41
Q

What is used as the heat removing medium ?

A

Generally, air

42
Q

What is the function of the expansion device ?

A

Control the amount of flow of refrigerant

43
Q

What is another function of the expansion device ?

A

Reduces pressure of condensed refrigerants

44
Q

What does this facilitate for the refrigerant ?

A

Lower temperature at constant enthalphy

45
Q

What is enthalpy ?

A

Enthalpy is the amount of heat content used or released in a system at constant pressure

46
Q

What does the evaporator do ?

A

Provides heat transfer surface for refrigerant to increase temperature

47
Q

What are some of the other components of vapour compression system ?

A

Receiver and Refrigeration lines

48
Q

What does the receiver do ?

A

Stores the condensed liquid

49
Q

Why does the receiver store the condensed liquid ?

A

To maintain sufficient supply of liquid to evaporator

50
Q

What do the refrigeration lines do ?

A

Transfers refrigerant from one component to another

51
Q

Why does the discharge line do ?

A

Deliver high P, high T from compressor to condensor

52
Q

What do low temperature lines do ?

A

Deliver low P, low T vapours from evaporator to condensor

53
Q

What comes out of the compressor ?

A

High P and High T vapours

54
Q

What comes out of the condensor ?

A

Liquid, which is at low T, but high T

55
Q

What comes out of the expansion valve ?

A

Pressure reduces at constant pressure

56
Q

What kind of energy does vapour absorption use ?

A

Heat

57
Q

Which part does vapour Absorption eliminate ?

A

Compressor

58
Q

How does vapour absorption handle vapours ?

A

Absorbed in a liquid, pumped to a generator which is heated for vapours to form

59
Q

What are two common absorbent refrigerant pairs in vapour absorption cycle ?

A

Ammonia - Water

Water - Lithium Bromide

60
Q

What is the replacement for compressor in vapour absorption cycle ?

A

Absorber, generator, throttled valve and pump

61
Q

Where is the Ammonia- Water mixture kept ?

A

Generator

62
Q

Where does the heat energy come from ?

A

An external source

63
Q

Where do the Ammonia vapours go ?

A

Flow to the condensor through pump

64
Q

What happens to the vapour in the condensor ?

A

Reject heat externally

65
Q

What happens to the vapours in the throttle valve ?

A

Both temperature and pressure fall

66
Q

What happens to the liquid ammonia in the refrigeration ?

A

They evaporate

67
Q

How do they evaporate ?

A

By absorbing the latent heat of vaporisation

68
Q

What does this achieve ?

A

Produces refrigeration effect

69
Q

What happens to the newly formed vapours now ?

A

It enters the absorber

70
Q

What happens in the absorber ?

A

Weak solution of Ammonia absorbs ammonia to form a strong solution

71
Q

Where does the weak solution of Ammonia come from ?

A

The throttle valve

72
Q

What happens to the strong solution of Ammonia ?

A

It is pumped to the generator

73
Q

Does it take a lot of energy to pump ?

A

No, it is negligible compared to the heat produced and refrigeration effect

74
Q

What is the COP of Vapour Absorption in comparison to Vapour Compression in the same temperature ?

A

It is 20-30% of the COP at the same temperature

75
Q

What are room air conditioners also known as ?

A

Window air conditioners

76
Q

What is the basic function of a window air conditioner ?

A

To provide filtered cool air, and maintain desired temperature

77
Q

Where is the refrigerant kept in room air conditioners ?

A

Compressor

78
Q

Where is it sent after being compressed ?

A

It is cooled in the condensor

79
Q

Why is the refrigerant passed through a filter drier ?

A

Any moisture is absorbed

80
Q

How is the liquid refrigerant reduced to low pressure ?

A

By passing it through the capillary tube

81
Q

What is a capillary tube ?

A

A narrow tube (hair-like thickness)

82
Q

Where does the capillary tube take the liquid refrigerant ?

A

Into the evaporator

83
Q

What does the evaporator fan do ?

A

It flows the air over the evaporator

84
Q

What happens to the refrigerator when the air flows over the evaporator ?

A

The refrigerator evaporates

85
Q

Are the evaporator and condenser fan run by the same motor ?

A

Yes, but in the opposite direction

86
Q

Where is the final filter kept ?

A

In front of the evaporator, to filter cooled air and allow it to enter the room

87
Q

Why is air recirculated ?

A

Because the occupants of the room heat the air

88
Q

How much of air is exhausted ?

A

About 10%

89
Q

Why does exhaust ventilator have damper ?

A

To control the amount of air exhausted into atmosphere

90
Q

Why is there a decorative grill in front of the filter ?

A

To change the direction of air flow

91
Q

Why is there a tray below the evaporator ?

A

To collect the condensate over evaporator and drain it outside

92
Q

Why is there a thermostat in front to f the filter ?

A

To measure and control temperature of air entering room

93
Q

Why are some safety devices incorporated in compressor ?

A

To protect against high pressure delivery, high motor temperature, etc.

94
Q

How is the compressor sealed in room air conditioner ?

A

Hermetically (Air tight)

95
Q

What is refrigeration ?

A

Process of moving heat from one place to another

96
Q

What is refrigeration system ?

A

Equipment employed in maintaining object at lower temperature

97
Q

What is refrigeration effect ?

A

Amount of heat absorbed by the refrigeration system from the space or object to be cooled

98
Q

What is the unit of refrigeration ?

A

Ton, And in SI units, kW

99
Q

What is ton of refrigeration ?

A

It is the amount of ice formed or melted in 24 hours from 0 degree centigrade water

100
Q

What is ice making capacity ?

A

Amount of ice produced in one hour from the water a 0 degree celcius to 0 degree ice

101
Q

What is coefficient of performance (COP) ?

A

Ratio of refrigeration effect to work input

102
Q

What is relative COP ?

A

Ratio of actual COP to theoretical COP

Mechanical Engineering (8 decks)

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