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mech 4 > Refrigeration > Flashcards

Refrigeration Flashcards

1
Q

What is sensible heat

A

The heat required to change the temperature but not change the state of a substance

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2
Q

What is latent heat

A

The heat required to change the state of a substance without any change in temperature

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3
Q

What is superheat

A

When the substance goes above the boiling point, every degree over 100 is 1 degree of superheat (105 degrees would be 5 superheat)

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4
Q

Name the 3 ways heat can be transferred and how

A

Conduction: Heat transfer through a solid
Convection: Heat transfer through a liquid
Radiation: Heat transfer through a space

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5
Q

Name the pressure, volume and energy statement for boiling liquids

A

As pressure increases, volume decreases, requiring more energy to boil the liquid
As pressure decreases, volume increases, requiring less energy to boil the liquid

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6
Q

What is sub-cooling

A

When a substance cools and turns into a liquid and then drops below its boiling point it is sub-cooled.
Every degree below the boiling point is 1 sub-cool degree (90 degrees would have 10 degrees of sub-cooling)

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7
Q

Name the 4 components of the refrigeration system and their function

A

Compressor - Pumps refrigerant around the system.
Condenser - Uses sea water to cool the refrigerant, turning its state from a gas to a liquid.
Thermal expansion valve - Controls the flow rate of the refrigerant through the system. Decreasing or increasing depending on the temperature of the refrigerant leaving the evaporator.
Evaporator - The refrigerant flowing through the evaporator removes the heat from refrigerator / cold room. This changes the state of the refrigerant from a liquid to gas.

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8
Q

What is the condition of the refrigerant as it flows between the four components in the system

A

Compressor to condenser - High pressure, high temperature, gas
Condenser to TEV - High pressure, warm temperature, liquid
TEV to evaporator - Low pressure, very cold, liquid
Evaporator to compressor - Low pressure, cool, gas

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9
Q

What are the applied refrigerant system components and what do they do

A

LP Cut out - Stops compressor if pressure drops too low
HP Cut out - Stops compressor if pressure gets too high
Oil separator - Separates oil from refrigerant
Liquid receiver - Stores refrigerant during maintenance
Drier - Removes moisture from refrigerant
Sight glass - Indicates moisture in refrigerant (Yellow = moisture, Green = no moisture)

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10
Q

What are the 3 refrigeration procedures?

A

Defrosting
Leak detection
Lubrication

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11
Q

What are the methods of defrosting

A

Natural defrosting - every 3-6 months
Hot gas defrosting - max of 1h in 24h in 15m slots
Electrical heating coils - done for max of 1h in 24h

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12
Q

What are the methods of leak detection

A

Oil slicks - where oil is leaking, refrigerant will also leak
IRLDS - Infra-red leak detection system
Spectrolyne Dye and UV Lamp
Snoop - like soapy water
Halogen leak detector - hand held device

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13
Q

What oils do the RN use for lubrication

A

OM 70 - general purpose used for CFC/HCFC machine
SUNISO 3GS - synthetic oil used on t23 and t-boats
SW 68 - synthetic oil used with R134a refrigerants

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14
Q

What 3 methods are used to add oil to the compressor

A

Via sump filler plug
By hand pump
Through use of a dosing pot

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15
Q

What is the name of the agreement to phase out harmful ozone depleting substances / refrigerants and what are those substances

A

Montreal protocol
CFCs
HCFC
Halons

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16
Q

What is the name of the agreement to reduce all greenhouse gases and what are the names of those greenhouse gases

A

Kyoto agreement
CO2
HFC
PFC

17
Q

Name the refrigerant hazards

A

They are heavier than air and will displace oxygen
If exposed to high temperatures they produce Phosgene gas
Can produce cold burns if exposed to skin (Frost bite)
Decomposing fruit and veg can produce CO2

18
Q

What should you do if you get refrigerant in your eyes and skin

A

If refrigerant gets into the eyes, flush them out with water and get medical treatment
If refrigerant gets onto your skin, wash off immediately

19
Q

Procedure for entering a refrigeration compartment

A

Rating in charge is to be informed personal are entering and informed when compartment is vacant
Breathing apparatus is available in compartment
The high and low exhaust fans are running
No smoking at any time in the refrigeration area
The IRLDS is working and indicating safe
The personnel trapped warning lamps are in working order
Any rating entering must have a sentry outside
The internal door opening mechanism is working

20
Q

What is chilled water used to provide cooling for

A

Weapons systems
Radars
Ships computer systems
Air treatment units (ATUs)

21
Q

What is the major difference between the refrigerant and the chilled water plant in regards to components

A

The chilled water plant has a CHILLER instead of an evaporator

mech 4 (4 decks)

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