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3rd Year Millwright > Heat Exchangers > Flashcards

Heat Exchangers Flashcards

1
Q

why are finned tube heat exchangers not commonly used for intercooling on large compressor installations?

A

they would have to be extremely large to deal with the high pressures and temperatures

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2
Q

what is conduction?

A

the transfer of head through contact of the fluid and a metal surface

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3
Q

what does it mean to have forced convection in a heat exchanger?

A

using a fan or pump to move the heat

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4
Q

which type of flow is most desirable in a heat exchanger laminar or turbulent?

A

turbulent

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5
Q

which type of flow path is more efficient, counter flow, cross flow, or parallel?

A

counter flow

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6
Q

why is copper commonly used in heat exchangers?

A

very high thermal conductivity

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7
Q

what type of exchanger is the common radiator?

A

finned tube exchanger

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8
Q

why are the plates placed close together on the plate heat exchangers?

A

created a high heat transfer because of the relative large surface area

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9
Q

why is the spiral heat exchanger so efficient?

A

because the fluids have a true counterflow path

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10
Q

why is part of the water evaporated in a cooling tower?

A

because of the temperature change

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11
Q

an ___________ cooling tower has a fan that forces air OUT of the tower

A

induced

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12
Q

the heat exchanger that has a single pipe placed concentrically inside a larger pipe is called the ________________ exchanger

A

double pipe

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13
Q

what is the purpose of a zinc anode in a heat exchanger?

A

he’s a sacrifice, so the electrolyte action of the two fluids eats away at the zinc and not the pipes

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14
Q

what is the main disadvantage of using longer tubes in a shell and tube exchanger compared to short tubes

A

pressure drop

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15
Q

is the triangular or the square pitch tube pattern more efficient for heat transfer in a shell and tube exchanger?

A

triangular

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16
Q

baffles in shell and tube heat exchangers commonly serve two functions, what are they?

A

support the tubes
create turbulence
prevent dead by-pass areas

17
Q

why are baffles necessary for heat transfer in large shell and tube exchangers?

A
  • to support the tubes from vibration
  • to prevent fluid from taking the path of least resistance
  • surface area to cool the liquid
18
Q

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

A

impingement baffles

19
Q

which baffles are used to split the shell side flow into two or more passes, allowing more contact time between fluids?

A

longitudinal baffles

20
Q

what determines the number of tube side passes?

A

the number of baffles in the channel head

21
Q

which type of exchanger is commonly used in services with a low differential of thermal expansion?

A

fixed tubesheet

22
Q

which type of exchanger has the main disadvantage that the shell side cannot be mechanically cleaned?

A

fixed tube exchanger

23
Q

tube heat exchangers should have the dirty fluids routed on the __________ side since the bundle cannot be removed for cleaning. the ___________ side is restricted to clean fluids.

A

shell
tube

24
Q

what is the main advantage of the floating heat exchanger compared to the fixed tube type of exchanger?

A

allow for thermal expansion

25
Q

what is the major disadvantage of the floating heat exchanger compared to the floating head with a baking device type of exchanger?

A

large clearance at the head end of the pull through type

26
Q

which applications is it desirable to use a double tubesheet exchanger?

A

when the two fluids cannot mix

27
Q

why do smaller diameter tubes result in a more efficient heat transfer rate?

A

they have increased velocity which increases the turbulence

28
Q

an increase in pressure drop through the exchanger or a drop in heat exchange efficiency usually indicates __________________

A

cleaning is needed

29
Q

why should the flange bolts always be loosened at the bottom of the flange first when performing heat exchanger maintenance?

A

so the heat doesn’t bow into your face, it goes to the ground

30
Q

impingement baffle is located below the ___________ linlet line and it prevents erosion of the _____________ of the tubes

A

shell
outside

31
Q

zinc anodes are used to control _____________ action

A

electrolytic

32
Q

longitudinal baffles are used to increase _______________ pass

A

shell side

33
Q

what are drift eliminators in cooling towers used for?

A

capture most of the water that is being pulled out with airflow

34
Q

fins transfer heat from the tube by _______________

A

conduction

35
Q

list three purposes for segmental baffles

A

support the tubes
cause turbulence
prevent dead by-pass areas

3rd Year Millwright (21 decks)

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