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Mech theory 4 Refrigeration, ventilation, hydraulics and fresh water > Refrigeration and ventilation > Flashcards

Refrigeration and ventilation Flashcards

1
Q

What happens to a liquid you’re trying to boil if you increase pressure?

A

Volume decreases and more energy is required to boil it.

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2
Q

What happens when you’re trying to boil a liquid and you decrease the pressure?

A

Volume increases and less energy is required to boil it.

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3
Q

What are the 3 states of matter?

A
  1. Solid
  2. liquid
  3. Gas
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4
Q

What are the 3 methods of transferring energy? and what states of matter do they apply to?

A
  1. Conduction applies to solids
  2. Convection applies to Liquids
  3. Radiation applies to gas
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5
Q

True or false, Heat will only transfer from hot to cold.

A

True

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6
Q

What factor should be changed in order to change state and temperature?

A

Pressure

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7
Q

What is sensible heat?

A

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

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8
Q

What is latent heat?

A

The heat required to change the state of a substance without any change in it’s temperature.

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9
Q

What is superheat?

A

When a substance goes above it’s boiling point it is superheated. For every degree it goes above it’s boiling point it gains one degree of superheat.

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10
Q

How many degrees of superheat does does steam at 115 degrees Celsius have?

A

15 degrees of superheat.

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11
Q

Define sub-cooling

A

When a substance cools and condenses into liquid and then drops below it’s boiling point it is sub-cooled. For every degree below it’s boiling point it gains one degree of sub-cooling.

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12
Q

What degree of sub-cooling will water have at 90 degrees Celsius?

A

10 degrees of sub cooling.

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13
Q

What is the purpose of the compressor in the refrigeration system?

A

It pumps the refrigerant around the system.

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14
Q

What is the purpose of the condenser?

A

It uses sea water to cool the refrigerant changing it’s state from a gas into a liquid.

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15
Q

What is the purpose of the Thermal expansion valve? (TEV)

A

It controls the flowrate of refrigerant through the system.

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16
Q

What is the purpose of the evaporator?

A

The refrigerant flowing through the evaporator removes heat from the refrigerator. This action changes the state of the refrigerant from a liquid into a gas.

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17
Q

What is the condition of the refrigerant as it flows from the compressor to the condenser?

A

Hot gas at high pressure.

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18
Q

What is the condition of the refrigerant as it flows between the condenser to the Thermal expansion valve?

A

Warm liquid (sub cooled) At high pressure.

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19
Q

What is the condition of the refrigerant as it flows between the Thermal expansion valve to the evaporator?

A

Very cold, low pressure liquid

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20
Q

What is the condition of the refrigerant as it flows between the evaporator and the compressor?

A

Cool, low pressure. gas (super-heated)

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21
Q

State the purpose of the LP cut out.

A

Stops the compressor if the pressure drops too low.

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22
Q

State the purpose of the HP cut out.

A

Stops the compressor if the pressure gets too high.

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23
Q

State the purpose of the Oil separator.

A

Separates oil from the refrigerant.

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24
Q

State the purpose of the Liquid receiver.

A

Stores refrigerant during maintenance.

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25
Q

State the purpose of the drier.

A

Removes moisture from the refrigerant.

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26
Q

State the purpose of the sight glass.

A

Indicates moisture in the refrigerant.

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27
Q

If the sight glass is yellow what does it indicate?

A

Moisture is present.

28
Q

If the sight glass is green what does it indicate?

A

Moisture isn’t present.

29
Q

What is the purpose of Defrosting?

A

To remove an ice build-up on the evaporator coils.

30
Q

State the methods of defrosting.

A
  1. Natural defrost; carried out every 3 - 6 months
  2. Hot gas defrosting; this is done for a maximum of 1 hour in 24 in 15 minute slots.
  3. Electrical heating coils; This is also done for a maximum of 1 hour in 24.
31
Q

Why is it important to have methods of leak detection in place?

A

Refrigerant leaks are harmful to the environment and reduce refrigerant plant efficiency.

32
Q

State the methods of leak detection.

A
  1. Oil slicks.
  2. IRLDS infra-red leak detection system.
  3. Spectrolyne dye and UV lamp.
  4. Snoop
  5. Halogen leak detector
33
Q

How do oil slicks detect a refrigerant leak?

A

If oil is leaking from the compressor then refrigerant will be also be leaking.

34
Q

What are the 3 special lubricants that can be used in the compressor?

A
  1. OM70
  2. SW68
  3. Suniso 3GS
35
Q

Compressor lubricants are hygroscopic what does hygroscopic mean?

A

A hygroscopic substance will absorb moisture from the atmosphere.

36
Q

State the 3 ways lubricant is added to the compressor.

A
  1. Via a sump filler plug
  2. By a hand pump
  3. Through the use of a dosing pot
37
Q

What did the the Montreal protocol 1987 agree to phase out the use of?

A
  1. CFC’s
  2. HCFC’s
  3. Halons
38
Q

What do CFC’s, HCFC’s and Halons deplete?

A

The ozone.

39
Q

What did the Kyoto summit agree to reduce the production of?

A

Greenhouse gases

40
Q

State the greenhouse gases.

A
  1. CO2
  2. HFC
  3. PFC
41
Q

State the 3 hazards of working with refrigerant.

A
  1. They are heavier than air and will displace oxygen.
  2. If exposed to high temperatures they can produce phosgene gas.
  3. They can produce cold burns on skin (frost bite)
42
Q

Why are active methods of defrosting only done for 1 hour with a 24 hour period?

A

To prevent cooking of the refrigerant.

43
Q

What needs to be done if refrigerant gets into the eyes?

A

They need flushing with running water and then require medical treatment.

44
Q

What needs to be done if refrigerant gets onto the skin?

A

It requires washing off immediately.

45
Q

State the procedure for entering refrigeration compartments?

A
  1. The rating in charge of the watch is to be informed that personnel are entering the compartment, and informed when the compartment is vacated.
  2. Breathing apparatus is available at the machinery space access.
  3. The high and low exhaust fans are running.
  4. No smoking at any time in the refrigeration area.
  5. The IRLDS is working correctly and indicating safe.
  6. The personnel trapped warning lamps are in working order.
  7. Any rating entering the room are to be accompanied by another rating who remains outside the room as a safety number.
  8. The internal door opening mechanism is in correct working order.
46
Q

What systems does chilled water provide cooling for?

A
  1. Weapons systems
  2. Radars
  3. Ships computer systems
  4. Air treatment units (ATU’s)
47
Q

State the uses of ventilation

A
  1. Cooling of electronic equipment
  2. CBRN
  3. Habitability
  4. Main machinery space cooling
  5. Galley ventilation
48
Q

State the types of common filter

A
  1. Panel filter
  2. Supply filters
  3. Grease filters
  4. Lint filters
  5. Dust filters
  6. Flameproof gauzes
49
Q

What is a panel filter used for?

A

Re-circulating trunking associated with air conditioning systems

50
Q

What are supply filters made of and where are they used?

A

They are made of polyurethane and fitted in ATU’s

51
Q

What does ATU stand for?

A

Air treatment unit

52
Q

What are grease filters used for?

Where can they be found?

A
  1. They collect grease present in the air.

2. They are fitted to exhaust canopies above deep fat fryers.

53
Q

What is the purpose of a lint filter?

A

To prevent the accumulation of fluff and fibres in the laundry.

54
Q

Where are dust filters fitted?

A

They are fitted to computer and sonar instrument spaces and the sick bay.

55
Q

Where are flameproof gauzes fitted?

A

Inflammable stores, paint shops, hangers, vehicle decks and magazines.

56
Q

What does AFU stand for?

What special conditions is the AFU used for?

A
  1. Air filtration unit.

2. CBRNDC state 1 and condition ZULU ALFA.

57
Q

What are the 3 sections that make up an AFU?

A
  1. Pre-particulate filter
  2. Particulate filter
  3. Gas filter
58
Q

What is different from a chilled water system and a refrigeration system?

A

The chiller.

59
Q

Describe the citadel.

A

A chemical, biological and nuclear shelter formed by closing the ship down to an increased gas tight state.

60
Q

How does the citadel work?

A

By increasing the atmospheric pressure within the ship above external pressure using AFU’s

61
Q

When would the citadel be tested?

A
  1. Annually
  2. Prior to DED
  3. During Harbour acceptance trials
  4. During sea acceptance trials
  5. All ships will be required to carry out a citadel test during FOST work up.
62
Q

In an ATU what percentage of air is recirculated and what percentage is fresh air?

A

67% recirculated and 33% fresh air.

63
Q

What spaces would a fan supply and fan exhaust be used?

A

Machinery spaces, Galleys, Laundries, WC’s and bathrooms

64
Q

What spaces would fan supply and natural exhaust be used?

A

Workshops and store rooms.

65
Q

What spaces would natural supply and fan exhaust be used?

A

Inflam stores and paint lockers

66
Q

What spaces would a natural supply and natural exhaust be used?

A

Unoccupied compartments and lobbies.

Mech theory 4 Refrigeration, ventilation, hydraulics and fresh water (3 decks)

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