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HeatX Flashcards

1
Q

What flow path within a heat exchanger will reach an equilibrium in temperature half way between the two extremes

A

Parallel flow

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2
Q

What flow path within a heat exchanger will reach the cooler of the two temperature extremes given enough time

A

Counter flow

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3
Q

What flow path has the greatest efficiency for a given size

A

Counter flow

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4
Q

What is the primary purpose of the fins on a finned tube exchanger

A

To increase surface areas

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5
Q

Which of the heat exchangers has very efficient true counter flow

A

Spiral because of its continuous curving passages it creates high turbulence.

In turn the velocity of the fluid scrubs it clean. This exchanger is an excellent choice for fluids that tend to deposit sludge

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6
Q

Within cooling towers the heat exchange is dependent on

A

Evaporation

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7
Q

What is the purpose of the zink anodes in a shell and tube heat exchanger

A

To minimize electrolytic action within the heat exchanger

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8
Q

What heat exchanger has its capacity changed the easiest.

A

Plate

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9
Q

Cooling towers are commonly used to do what

A

Recycle water, the water to be cooled is pumped to the top of the tower where it is sprayed through a Nozel to give a fine spray, some evaporates cooling the remainder

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10
Q

What baffle is used to reduce erosion by entering fluids

A

Impigmant

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11
Q

What are the two common functions of shell side baffles

A

To increase turbulent flow and support the tube bundle

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12
Q

How many longitudinal shell baffles are required to get four passes

A

3

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13
Q

Which heat exchanger is limited to chemical cleaning of the tube side

A

U-tube

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14
Q

What heat exchanger is most likely to suffer from thermal stress causing tube sheet leakage

A

Fixed tube sheet

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15
Q

What’s the main advantage and disadvantage of the floating head exchanger

A

The advantage is it’s easier to clean

The disadvantage is the large clearance requirements needed

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15
Q

What is a disadvantage to the floating head outside-packed, lantern ring exchanger

A

If the exchanger leaks the fluids are exposed to the atmosphere

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16
Q

Where is a double tube sheet exchanger used

A

In applications where is is not desirable to have mixing of tube-side and shell-side fluids

It is impossible for this set up to have any mixing and will drip externally

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17
Q

What fluid usually flows through the tube side

A

The dirtier fluid as it’s easier to clean through the tubes

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18
Q

Higher pressure fluid flows through tubes of shell side?

A

Tube side as it could possible collapse the tubes if it flowed through shell side

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19
Q

The fluid with the lower heat transfer usually travels where?

A

The outside of the tubes, it’s cheaper and easier to add fins for heat transfer

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20
Q

What is TEMA

A

Tubular Exchanger Manufacturers Assosiation

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21
Q

What is the advantage of a floating head with split backing device

A

Allows for more tubes to fit in the shell while allowing for thermal growth

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22
Q

Heat transfer is primarily effected by what 5 causes

A 
Fluid flow
Temperature differentials 
Hearing surface area
Contact time
Conductivity

Other factors would consist of Fluid films
Thickness of heating surface
Cleanliness of hearing surface

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23
Q

What is a surface layer

A

A film or a fluid stuck to the metal wall

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24
Q

Cold start up is when….

A

You gradually start both fluids at the same time

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25
Q

Shutdown is when you….

A

Gradually stop both fluids at the same time

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26
Q

What are the three most common causes to Poor performance in heat exchangers

A

Leaking tube sheets
Fouling
Vibration

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27
Q

An increase in resistance to fluid flow and heat transfer due to undesired deposits is referred to as

A

Fouling

Deposit build up lowers heat transfer rate

28
Q

What should you never use to clean a heat exchanger

A

Steam

29
Q

It’s ok to screw eye bold I to the tube sheets

A

Yes, tubes are thin and bend easy so rigging on each end is most desirable

30
Q

Stress cracks in tubes are a sign of what

A

High stresses caused by continuous vibrations

31
Q

What is the purpose of hydrostatic testing

A

Used to check heat exchangers for leaks before and after overhauling - the standard for hydrostatic testing is 1-1/2 times the working pressure

32
Q

What precaution should be taken when loosening head studs.

A

Ensure exchanger has been purged vented and drained

Loosen bolts at the bottom first

33
Q

What happends if you check leaks with hot water

A

Expansion could seal the leak

34
Q

What pressure is normally used for hydrostatic pressure

A

1-1/2 times the working pressure

35
Q

How is the shell side of an exchanger cleaned.

A

Hot water or chemical

36
Q

What is the advantage of a pull through floating head exchanger

A

Larger clearance around tube bundle = less surface area

37
Q

How could you tell if there was a tube sheet leak on a double tube sheet exchanger

A

Drips between the two tube sheets

38
Q

She’ll and tube exchanger sizes are classified by

A

Shell Dia. and tube length

39
Q

Define the purpose of a heat exchanger.

A

To cool or heat liquid through a variety of processes

40
Q

Define conduction

A

The transfer of heat energy from one molecule to another or contact of fluid and a metal

41
Q

Define Convection

A

The result of the movement of mass of fluid (gas or liquid)from a warm location to a cooler one

42
Q

Define radiation

A

The transfer of energy by electro magnetic wave

43
Q

Different materials have different rates of thermal expansion

What potential problems in a heat exchanger are related to this.

A

Loosening of joints

44
Q

Different materials have different rates of thermal expansion

Name two exchanger designs that illuminate this problem

A

Utube

Floating head

45
Q

Three advantages of uTube exchanger

A

Both ends are fixed illuminating thermal expansion problems

Easy to remove and clean

Well suited for high-temp/high pressure

46
Q

What’s the most common way a tube is attached to a tube sheet

A

Expansion into tube sheet

Rolled in
And welding are the other two types

47
Q

The rate of heat transfer is effected by

A

Temperature difference
Area of contact
Conductivity of metal
Nature of substance

48
Q

What flow is most desirable in a heat exchanger

A

Turbulent flow

Scrubs the walls allowing more heat transfer

49
Q

Mixed flow is common where

A

In heat exchangers with baffles that cause the flows to Switch between parallel and counter flow

50
Q

What flow PATH is more desirable

A

Counter flow is more efficient

51
Q

What type of exchanger is a common radiator

A

Finned tube

Greater surface area

52
Q

Why are spiral heat exchangers so efficient

A

Both fluids have true contour

Dead bypasses are illuminated

Less fouling

53
Q

Why is part of the water evaporated in the cooling tower

A

The heat to evaporate is drawn from the remaining water

Resulting in a temp drop in the reaming water

54
Q

What type of cooling tower has a fan that forces the water out

A

Induced draft

55
Q

The heat exchanger that has a pipe concentric inside another pipe is called

A

Double pipe

Perfect for high pressure
Designed for counter flow current

56
Q

What baffles are normally provided over the tubes to reduce erosion by the entering fluid

A

Impigman baffles

57
Q

What baffle is used to split the shell side flow

A

Longitudinal

58
Q

Mixed flow is common where

A

In heat exchangers with baffles that cause the flows to Switch between parallel and counter flow

59
Q

What flow PATH is more desirable

A

Counter flow is more efficient

60
Q

What type of exchanger is a common radiator

A

Finned tube

Greater surface area

61
Q

Why are spiral heat exchangers so efficient

A

Both fluids have true contour

Dead bypasses are illuminated

Less fouling

62
Q

Why is part of the water evaporated in the cooling tower

A

The heat to evaporate is drawn from the remaining water

Resulting in a temp drop in the reaming water

63
Q

What type of cooling tower has a fan that forces the water out

A

Induced draft

64
Q

The heat exchanger that has a pipe concentric inside another pipe is called

A

Double pipe

Perfect for high pressure
Designed for counter flow current

65
Q

What baffles are normally provided over the tubes to reduce erosion by the entering fluid

A

Impigman baffles

66
Q

What baffle is used to split the shell side flow

A

Longitudinal

67
Q

What is the main disadvantage of the floating head exchanger compared to the floating head with the baking device

A

The disadvantage of the pull through exchanger is the the large clearance requirements between outer tubes and shell

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