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mechanical theory 4 > Refrigeration > Flashcards

Refrigeration Flashcards

1
Q

What happens when you boil a liquid at high pressure?

A

The volume will decrease & more energy will be required.

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2
Q

What happens when you boil a liquid at low pressure?

A

The volume will decrease and less energy will be required.

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3
Q

What is heat transfer?

A

Heat will always travel from hot to cold.

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4
Q

What are the three ways that heat can be transferred?

A

Conduction: This is heat transfer through a solid.
Convection: This is heat transfer through a liquid.
Radiation: This is heat transfer through space/air.

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5
Q

Explain sensible heat.

A

This means the heat is required to change temperature, the state of the substance will not change. Such as feeling the heat from the sun.

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6
Q

Explain latent heat.

A

This means that the heat is required to change the state of a substance with out any change in its temperature. Such as boiling a pan of water until it has all evaporated. The temperature will not change as it will be 100c.

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7
Q

Explain superheat.

A

when a substance goes above its boiling point. For every degree above its boiling point it will gain a degree of superheat.

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8
Q

Explain sub-cooling.

A

When a substance cools and condenses into liquid and will drop bellow its boiling point it will be called sub-cooling. For example if water is 90c it will have 10c of sub-cooling.

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9
Q

What temperature is a cold room and what is stored inside?

A

-18 to -22 Frozen meats will be stored in here.

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10
Q

What temperature will the Cold room dairy be?

A

+4 to +6 Dairy and butter will be stored in here.

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11
Q

What is the temperature of the fruit and vegetable store?

A

+4 to +6

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12
Q

What is the temperature of the Galley ready to use cupboard?

A

+5 to +7

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13
Q

What are the four parts of the basic refrigeration system and explain them.

A
  1. Compressor - This pumps the refrigerant around the
    system. Heating up the gas and pressurising it. Similar to the prime mover.
  2. Condenser - This uses sea water to cool the refrigerant, changing its state from gas into a liquid.
  3. TEV (thermal expansion valve) - This will control the flowrate of the refrigerant through the system. This can also increase or decrease the flow depending on the temperature of the refrigerant leaving the evaporator.
  4. Evaporator - The refrigerant that is flowing through the evaporator removes heat from the refrigerator/cold room. by doing this the state of the refrigerant will change from a liquid into a gas.
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14
Q

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

A

Compressor to Condenser – Hot, High Pressure, Gas

Condenser to TEV – Warm, High Pressure, Liquid (Sub-cooled)

TEV to Evaporator – Very Cold, Low Pressure, Liquid

Evaporator to Compressor – Cool, Low Pressure, Gas (Super-Heated)

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15
Q

Explain LP cut out.

A

LP cut out is where compressor is stopped if the pressure drops to low.

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16
Q

explain HP cut out.

A

HP cut out is where the compressor is stopped if the pressure is to high

17
Q

What is the oil separator?

A

this separates the oil from the refrigerant.

18
Q

What is the liquid reciever?

A

This stores the refrigerant whilst maintenance is being undertaken.

19
Q

What does the drier do?

A

This removes moisture from refrigerant.

20
Q

Explain the sight glass

A

This indicates moisture in the refrigerant.
If yellow is indicated there is moisture in the system.
If green is indicated there is no moisture.

21
Q

Explain the defrosting step in the refrigeration procedures.

A

This is required when ice is built up on the evaporator coils.
There are 3 methods of defrosting:
Natural defrost which is carried out every 3 to 6 months.
Hot gas defrost which is done for a maximum of 1 hour in 24 in 15 minute slots.
Electrical heating coils this is also done for a maximum of 1 hour in 24.

22
Q

Explain leak detection.

A

If refrigerant leaks it can be harmful so leak detection is put into place. The methods are:
* Oil slicks – where oil is leaking there will also be refrigerant leaking
* IRLDS Infra-red leak detection system
* Spectrolyne Dye and UV Lamp
* Snoop (similar to soapy water)
* Halogen Leak Detector (Hand held electronic device)

23
Q

What special lubricants does the compressor use?

A

OM70 & SW68

24
Q

What does hydroscopic mean?

A

Absorb moisture from the atmosphere.

25
Q

When lubricating the compressor what should you use?

A

A fresh can of oil as only new cans of oil should be used.

26
Q

What methods can oil be added to the compressor?

A

3 methods:
Sump filler plug
Hand pump
Dosing pot.

27
Q

What is the Montreal protocol

A

Agreement to phase out harmful ozone depleting substances / refrigerants such as:
* CFCs
* HCFC
* Halons

28
Q

What is the Kyoto summit

A

This is the agreement to reduce all greenhouse gasses such as
co2
HFC
PFC

29
Q

What are the refrigerant hazards

A

They are heavier than air and will displace Oxygen

If exposed to high temperatures they can produce PHOSGENE GAS

Can produce Cold Burns on exposed skin (Frost Bite)

Decomposing Fruit and Veg can produce CO² there for a gas monitor will be needed.

30
Q

What is the procedure for entering a refrigeration department

A
  • The Rating in charge of the watch is to be informed that personnel are entering the compartment, and informed when the compartment is vacated
  • Breathing Apparatus is available at the machinery space access
  • The high and low exhaust fans are running
  • No smoking at any time in the refrigeration area. Any hot work is to be very tightly controlled
  • The Infra-Red Leak Detections System (IRLDS) is working correctly and indicating safe
    The personnel trapped warning lamps are in working order
    Any rating entering the room is to be accompanied by another rating who remains outside the room as a safety number
    The internal door opening mechanism is in correct working order

mechanical theory 4 (4 decks)

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