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2nd Year Finals > Theory > Flashcards

Theory Flashcards

1
Q

What is the approach & the range when talking about cooling towers?

A

The measure of performance.

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2
Q

How do you calculate the approach?

A

Water Outlet of cooling tower - wet bulb temperature

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3
Q

how do you calculate the range?

A

Water In - Water out

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4
Q

One example of a type of non-evaporative water-cooled condenser?

A

Dry Cooler

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5
Q

What is the difference between an indirect and a direct cooling tower?

A

A direct cooling tower is open to atmosphere. An indirect cooling tower is a closed loop system (not exposed, in a tube) that uses multiple cooling sources

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6
Q

What is the difference between an evaporative condenser and a indirect cooling tower?

A

An evaporative condenser’s tubes are filled with high pressure refrigerant. An indirect cooling towers tubes are filled with water or glycol

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7
Q

What applications are evaporative condensers used and why?

A

Ammonia (R-717) because evaporation is great at removing heat and ammonia has a high discharge temperature.

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8
Q

Waste Water Condensing systems reject the heat absorbed by the water where?

A

Floor Drain

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9
Q

In a waste water condensing system what valve regulates discharge pressure?

A

A direct acting water regulating valve

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10
Q

Dry Coolers use evaporation, true or false?

A

False

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11
Q

What is the purpose of the fill in a cooling tower?

A

Increase the surface area of the water.

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12
Q

What is the job of spray headers or distrubtuion throughs?

A

keep the fill wetted for optimal heat exchange

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13
Q

What is the job of a drift eliminator in a cooling tower/evaporative condenser?

A

Stop water from leaving the equiptment

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14
Q

What is the difference between forced draft and induced draft cooling towers

A

Forced draft has a fan at the bottom of the tower that mechanically pushes ambient air through the tower. Induced draft pulls air through the tower rather than pushing it. The fan is located at the top.

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15
Q

What is the calulation for finding a cooling towers efficency?

A

=Range/Range + Approach

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16
Q

A lower wet bulb temperature will effect the capacity of the cooling tower how?

A

Increase in capacity with dry air

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17
Q

Tower Bypass is a type of wat for cooling towers?

A

Capacity Control

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18
Q

Explain what a tower bypass does?

A

Maintains a minimum condenser water return temperature in low ambient conditions to prevent freeze up

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19
Q

What is the advantage of an induced draft cooling tower?

A

Losses less water to drift

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20
Q

Three types of evaporators are?

A

Dry Expansion, Flooded, & Liquid Recirculation (Liquid overfeed)

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21
Q

In a Dry Expansion Evaporator where is the refrigerant?

A

In the tubes

22
Q

Tube and Shell is a type of flooded evaporator, true or fale?

A

True

23
Q

Liquid overfeed is used in what type of application?

A

Multiple evaporator installations. Large cold storage operations. Industrial

24
Q

How is the refrigerant circulated through the evaporator in a liquid overfeed system?

A

Liquid refrigerant pump

25
Q

How much superheat is expected in a flooded evaporator?

A

No Superheat - Vapour leaving the evaporator is at Saturation Temperature

26
Q

Three types of air cooling evaporators?

A

Bare Tube, Finned Tube, Plate Type

27
Q

What are the purpose of the fins in a Finned Tube evaporator?

A

Increase surface area.

28
Q

What determines the fin spacing?

A

Coil operating temperature (To accommodate frost)

29
Q

What happens to the relative humidity if the Temperature Difference increase?

A

Decreases

30
Q

Counter flow decreases heat transfer efficency? True of False?

A

False. It increases heat transfer.

31
Q

Which forced convection evaporator has a better throw, Draw through or Blow Through?

A

Draw Through

32
Q

Which forced convection evaporator has a better humidification, Draw through or Blow Through?

A

Blow through (Due to lower air velocity)

33
Q

What is the primary and secondary surfaces of a Fine and Tube Evaporator?

A

Primary = Tubes
Secondary = Fins

34
Q

A thicker slab evaporator will have a greater or lesser dehumidification ability

A

Greater

35
Q

When is a defrost cycle required?

A

Evaporator SST is below freezing point of water.

36
Q

6 Methods of Defrost

A

Manuel, off-cycle, hot gas, spray, electric, “Cool” gas

37
Q

Off-Cycle defrosts often use this temperature sensing device..

A

Constant Cut-In

38
Q

What is the purpose of a re-evaporator coil in a hot gas defrost?

A

adds heat from the ambient air to the hot gas defrost cycle to aid in defrost of the coil.

39
Q

What is the difference between boiling and evaporation?

A

Boiling requires heat and evaporation does not

40
Q

Why don’t we use H20 as a refrigerant?

A

1) Because it freezes at 32 F
2) It rejects oil
3) Its corrosive

41
Q

In a lithium bromide absorber refrigeration system, what is the refrigerant?

A

Water

42
Q

In a lithium bromide absorber refrigeration system, what is the absorber?

A

Lithium Bromide

43
Q

Liquid evaporation stops when …?

A

Wet Bulb = Dry Bulb

44
Q

In an ammonia absorbtion system, what is the refrigerant?

A

Ammonia

45
Q

In an ammonia absorption system, what is the absorber?

A

Water

46
Q

Why is it called a propane refrigration system?

A

Because Propane is the heat source that is needed

47
Q

What does a postive displacement compressor do?

A

Increases the pressure by decreasing the volume (Squeezes)

48
Q

What does a non-positive displacement compressor do?

A

Increases the pressure of a refrigerant vapour by accelerating low pressure & low velocity refrigerant via motor impeller

49
Q

3 Compressor Categories

A

1) Open
2) Hermetic
3) Semi-Hermetic

50
Q

How do we use capacity control for centrifigual compressors?

A

Guiding Vanes (act like shutters to open/close access to the impeller)

51
Q

What device is used in screw compressors for capacity control?

A

Slide Valve

2nd Year Finals (3 decks)

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