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Millwright Third Year 2018 > Industrial Refrigeration > Flashcards

Industrial Refrigeration Flashcards

1
Q

How do most refrigeration systems produce cold?

A

The vapour compression cycle.

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2
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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3
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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4
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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5
Q

What is latent heat of vaporization?

A

The quantity of heat required to completely vaporize 1kg of a liquid. The reverse process is called latent heat of condensation.

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6
Q

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

A

As the pressure increases, a higher temperature is required.

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7
Q

Compressing a vapour does what ?

A

It increases its pressure, and temperature.

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8
Q

What are the boiling points of propane, and ammonia?

A

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

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9
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.

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10
Q

What is the vapour compression cycle?

A
  • Evaporator
  • Compression,
  • Condenser,
  • Metering device (expansion chamber)
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11
Q

What is superheating

A

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

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12
Q

What is sub cooling?

A

The removal of heat from a saturated liquid.

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13
Q

What must be available for a liquid to vaporize?

A

Heat.

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14
Q

What is the compressors function?

A

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

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15
Q

What is the condensers primary function?

A

To reject the heat from the circuit.

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16
Q

What are the three (3) types of condensers?

A
  • Air cooled
  • Water cooled
  • Evaporative condenser.
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17
Q

Out of the three (3) condensers which is the most effective?

A

Water Cooled Condencer.

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18
Q

What are the two types of water cooled condensers?

A
  • Waste Water System
  • Recirculated System.

NOTE: If a recirculated system is used, a cooling tower must be used.

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19
Q

What is an evaporative condenser?

A

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

20
Q

What is the metering device?

A

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

21
Q

What are the different types evaporators?

A
  • Frosting Or Non Frosting,
  • Liquid Type Or Air Type.

NOTE: These are decided by what they cool (air or liquid)

22
Q

What is the designation for copper piping used for refrigeration system

A

ACR tubing, and it is sized by the ID.

23
Q

What systems cannot use copper tubing?

A

Ammonia and propane systems

24
Q

What are the typical applications for ammonia and propane systems

A
  • Propane is used in natural gas processes.

* Ammonia is used in larger buildings.

25
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 get it warmer.

26
Q

What is moisture in a refrigeration system?

A

It is a contaminant. It will freeze inside the system.

27
Q

What lubricates the compressor?

A

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

28
Q

Where are oil separator always used?

A

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

29
Q

What is the primary function of a chilled water circuit?

A

They are used on larger air conditioning systems.

30
Q

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

A

It is vulnerable to surging.

31
Q

What refrigerant is used typically in a chilled water circuit?

A

R-22 or R-134a

32
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.

33
Q

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

A

It flows into a low pressure, or low side receiver.

Because you can not have fluids flow into the compressor.

34
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.

35
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 or Hot Gas.

36
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

37
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.

38
Q

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

A

They must have a surge tank.

39
Q

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

A
  • Primary System-Ammonia

* Secondary System-Brine

40
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

41
Q

What is an absorption refrigeration circuit also known as?

A

Lithium bromide system

42
Q

Where are absorption circuits used?

A

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

43
Q

How many separate circuits are in a absorption circuit?

A
  • Chilled water circuit
  • Cooling tower circuit
  • Refrigerant water circuit
44
Q

Where is the compressor in an absorption refrigeration circuit?

A

“There is no compressor”

NOTE: 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

45
Q

Why is the absorption method tough to maintain?

A

Because the entire absorption system must be kept gas tight.

46
Q

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

A

They must have a surge tank.

Millwright Third Year 2018 (15 decks)

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