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Third Year Millwright > Insulation/refrigeration > Flashcards

Insulation/refrigeration Flashcards

1
Q

What is another application for insulation?

A

Sound proofing

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2
Q

What three ways can heat be transferred?

A

Conduction, convection, radiation

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3
Q

What are some purposes of insulation?

A

Keeps thing warm, or cool, which increases efficiency. It also protects damage due to exposure due to heat, or corrosive atmospheres. Another common application is to prevent water condensation on cold surfaces.

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4
Q

What are the three insulation categories?

A

Cryogenic (below -10 1°C)
Thermal (between -10 1°C to 815°C)
Refractory (above 815°C)

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5
Q

What is cryogenic insulation?

A

It is used in the temperature range of -101 down to absolute zero. Cryogenics often is used to keep liquified gasses in the liquid state.

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6
Q

How are containers for cryogenics constructed?

A

In an insulated material to withstand extremely low temperatures without losing their strength. Usually a container inside a container similar to a thermos

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7
Q

What is cellular glass?

A

It is a common cryogenic range insulation. It is light weight rigid material made up of millions of completely sealed glass cells and each one in an isolated space. It is extremely abrasive.

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8
Q

What is super insulation?

A

The term applied to insulating blankets developed for spaceflight. The blanket consists of approximately 50 to 100 layers per inch of aluminized mylar separated by thin air spaces

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9
Q

Describe thermal insulation.

A

Most common type of insulation, there are three subcategories of thermal insulation- low temp, intermediate temp, high temp
Typical materials are fibreglass, rock wool, foamed plastics

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10
Q

What is effectively used in insulating building materials?

A

Small air pockets in the material greatly increase its insulation

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11
Q

What are the three thermal insulation categories?

A

Fibrous
Cellular
Granular

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12
Q

Describe fibrous insulation

A

Made from long small diameter fibers that divide the air into many tiny compartments. Fiberglass and mineral wool are commonly used

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13
Q

Describes cellular insulation

A

Use the principle of dividing the air pockets into tiny compartments. Foamed in plastics such as polystyrene and polyurethane are common

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14
Q

What is granular insulation

A

It is a loose horrible material such as vermiculite. Did commonly is used to fill the void inside hollow brick walls.

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15
Q

Define Refractory insulation

A

Typical applications are steel foundries and cement and lime kilns. The different forms of refracture he insulation available are: castable refractories, standard and specially shaped bricks, gunnite mixes, ramming mixes

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16
Q

What is a castable refractory

A

Made of minerals that withstand high temperature in the way they form ceramic, glass, or crystalline bond with manufactured.

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17
Q

What are refractory bricks?

A

They are used to line the surface of a kiln. The bricks are non conducting, and thick enough to keep the steel shell from becoming red hot and warping

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18
Q

What is gunnite?

A

It is mixed to a specific consistency, similar to mixing concrete, and is then sprayed onto the surface

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19
Q

What is a ramming mix?

A

Has the consistency of thick plasticine. These mixes are used mainly for patching and for filling in small areas where it is too difficult to cut bricks to match

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20
Q

What things are considered when selecting insulation

A

Thermal properties, mechanical properties, and chemical properties

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21
Q

What is temperature conductivity?

A

Thermal conductivity is similar to thermal conductance except that conductivity is rated on a 1 inch thick section of insulation. It is known as the K value. The lower the number the better the K factor is

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22
Q

What is thermal resistance?

A

It is the resistance to flow through a unit of area. It is known as the R value, and the higher the number, the better

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23
Q

Define insulation

A

Any material that is a poor conductor of heat or electricity that is used to stop or slow down the flow of heat or electricity

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24
Q

Another use for insulation other than stopping heat transfer

A

Noise control

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25
Q

Prolonged noise over ___db is not considered safe

A

70

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26
Q

What are some methods of sound control

A

Moveable curtains can reduce noise by 25db

Curtains with core acoustic insulation

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27
Q

What is cladding?

A

Also called jacketing. Protects the insulation from moisture and in some cases UV rays

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28
Q

What are some materials for cladding?

A

Aluminum sheeting, stainless steel for sheeting, pvc, woven tape, cloth sheets, plastic, foil laminates, roofing felt

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29
Q

As much as 98% of insulation problems are related to_____

A

Moisture

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30
Q

What is the purpose of a moisture barrier?

A

Prevents condensation from getting into the insulation. It is always put on the warm side of the insulation

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31
Q

How do most refrigeration systems produce cold?

A

The vapour compression cycle.

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32
Q

What is energy?

A

It is the capacity to do work, and can exist as potential energy, or as kinetic energy.

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33
Q

Explain energy conversion

A

In a refrigeration cycle, electrical energy is brought in, which is converted to mechanical energy through a motor then produces heat energy as it is running.

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34
Q

When one form of energy disappears, what happens?

A

Another form of energy appears. Energy can not be created or destroyed.

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35
Q

What is latent heat of vaporization?

A

The quantity of heat required to completely vaporize one kg of a liquid. The reverse process is called latent heat of condensation

36
Q

How does a pressure increase change the boiling point of a liquid?

A

As the pressure increases, a higher temperature is required

37
Q

Compressing a vapour does what ?

A

It increases its pressure, and temperature.

38
Q

What are the boiling points of propane, and ammonia?

A

Propane boils at -42°C
Ammonia boils at -33°C
At atmospheric pressure

39
Q

What components are on the high pressure side and low pressure side?

A

The low pressure side starts from the outlet of the metering device and continues as the refrigerant flows to the inlet of the compressor through the evaporator. high-pressure side starts on the inlet of the compressor through the condenser and back to the inlet of the metering device

40
Q

What is the vapour compression cycle?

A

Compression,condenser, metering device (expansion chamber), evaporator

41
Q

What is superheating

A

The addition of heat to a vapour, which elevates the temperature higher than the boiling point

42
Q

What is sub cooling?

A

The removal of heat from a saturated liquid

43
Q

What must be available for a liquid to vaporize?

A

Heat

44
Q

What are the components, in order, of the vapour compression refrigeration cycle

A

Compressor
Condenser
Metering device(expansion)
Evaporator

45
Q

What is the compressors function?

A

It is a vapour pump, and is the prime mover of the refrigerant

46
Q

What is s condensers primary function?

A

To reject the heat from the circuit

47
Q

What are the three types of condensers, and which is most effective?

A

Air cooled, water cooled, evaporative condenser.

48
Q

What are the two types of water cooled condensers?

A

Waste water system, recirculated system. If a recirculated system is used, a cooling tower must be used.

49
Q

What is an evaporative condenser?

A

Much like a cooling tower., it uses both water and air to cool the refrigerant

50
Q

What are the components, in order, of the vapour compression refrigeration cycle

A

Compressor
Condenser
Metering device(expansion)
Evaporator

51
Q

What is the compressors function?

A

It is a vapour pump, and is the prime mover of the refrigerant

52
Q

What is s condensers primary function?

A

To reject the heat from the circuit

53
Q

What are the three types of condensers, and which is most effective?

A

Air cooled, water cooled, evaporative condenser.

54
Q

What are the two types of water cooled condensers?

A

Waste water system, recirculated system. If a recirculated system is used, a cooling tower must be used.

55
Q

What is an evaporative condenser?

A

Much like a cooling tower., it uses both water and air to cool the refrigerant

56
Q

What is the metering device?

A

It is used as a pressure reducer. They are basically an adjustable flow restrictor

57
Q

What are the different types evaporators?

A

Frosting or non frosting, liquid type or air type. These are decided by what they cool (air or liquid)

58
Q

What is the designation for copper piping used for refrigeration system

A

ACR tubing, and it is sized by the ID

59
Q

What systems cannot use copper tubing?

A

Ammonia and propane systems

60
Q

What is the metering device?

A

It is used as a pressure reducer. They are basically an adjustable flow restrictor

61
Q

What are the different types evaporators?

A

Frosting or non frosting, liquid type or air type. These are decided by what they cool (air or liquid)

62
Q

What is the designation for copper piping used for refrigeration system

A

ACR tubing, and it is sized by the ID

63
Q

What systems cannot use copper tubing?

A

Ammonia and propane systems

64
Q

What are the typical applications for ammonia and propane systems

A

Propane is used in natural gas processes, and ammonia is used in larger buildings

65
Q

If liquid ammonia is splashed on your skin or clothing, what is the procedure?

A

Do not remove clothing, but try to hold it away from your skin. Gradually flush area with cool water slowly getting warmer.

66
Q

What is moisture in a refrigeration system?

A

It is a contaminant. It will freeze inside the system

67
Q

What lubricated the compressor?

A

There is a small amount of oil that is in the refrigeration circuit.

68
Q

Where are oil separator always used?

A

Always in ammonia systems, because oil and ammonia are not mixable

69
Q

What is the primary function of a chilled water circuit?

A

Larger air conditioning systems

70
Q

What is a centrifugal compressor vulnerable to in a chilled water circuit?

A

It is vulnerable to surging

71
Q

What refrigerant is used typically in a chilled water circuit?

A

R-22 or R-134a

72
Q

What is a liquid over feed system?

A

It is where more refrigerant is pumped into the system than is needed. At the exit over the evaporator, some of the refrigerant is still a liquid

73
Q

If some of the refrigerant is still a liquid after the evaporator, where does it go?

A

Because you can not have fluids flow into the compressor, it flows into a low pressure, or low side receiver

74
Q

What is the benefit of the liquid over feed system?

A

It ensures all heat transfer is latent transfer, it reacts quickly to high demand changes, it is easily modified, putting more evaporators in the circuit, or removing them quickly

75
Q

How is defrosting of the evaporators done in a liquid over feed system?

A

Sometimes they use electric heaters, ,but because plenty of hot vapours are available they sometimes use those hot vapours

76
Q

Describe a flooded refrigeration system

A

It is the type that is used in hockey arenas. It has two separate systems, one for the refrigerant and one for the brine

77
Q

Why do they call it a flooded refrigeration system?

A

Because the brine is completely immersed or flooded in the refrigerant. It uses a shell and tube system for the two solutions

78
Q

What must a flooded refrigeration system have to prevent fluids from entering the compressor?

A

They must have a surge tank

79
Q

What is the primary system and what is the secondary system of a flooded refrigeration system?

A

Primary system-ammonia

Secondary system- brine

80
Q

What are two safety systems or features to keep public safe using this system?

A

The brine tank is vented so if any ammonia gets in there, it will go out the vent. If there is a fire, a button can be pushed to vent the pressurized ammonia out the top of the building, from the sealed ammonia compressor room

81
Q

What is an absorption refrigeration circuit also known as?

A

Lithium bromide system

82
Q

Where are absorption circuits used?

A

They were used in high volumes buildings such as hospitals. They are seldom used now

83
Q

How many separate circuits are in a absorption circuit?

A

Three
Chilled water circuit
Cooling tower circuit
Refrigerant water circuit

84
Q

Where is the compressor in an absorption refrigeration circuit?

A

There is no compressor, heat energy is used instead. The lithium bromide absorbs the moisture, and when it becomes saturated, it goes through a steam generator to charge it again

85
Q

Why is the absorption method tough to maintain?

A

Because the entire absorption system must be kept gas tight

86
Q

What must a flooded refrigeration system have to prevent fluids from entering the compressor?

A

They must have a surge tank

87
Q

What is the primary system and what is the secondary system of a flooded refrigeration system?

A

Primary system-ammonia

Secondary system- brine

Third Year Millwright (12 decks)

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