Heat Exchangers

Question 1

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

Answer 1

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

Question 2

what is conduction?

Answer 2

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

Question 3

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

Answer 3

using a fan or pump to move the heat

Question 4

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

Answer 4

turbulent

Question 5

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

Answer 5

counter flow

Question 6

why is copper commonly used in heat exchangers?

Answer 6

very high thermal conductivity

Question 7

what type of exchanger is the common radiator?

Answer 7

finned tube exchanger

Question 8

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

Answer 8

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

Question 9

why is the spiral heat exchanger so efficient?

Answer 9

because the fluids have a true counterflow path

Question 10

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

Answer 10

because of the temperature change

Question 11

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

Answer 11

induced

Question 12

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

Answer 12

double pipe

Question 13

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

Answer 13

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

Question 14

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

Answer 14

pressure drop

Question 15

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

Answer 15

triangular

Question 16

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

Answer 16

support the tubes
create turbulence
prevent dead by-pass areas

Question 17

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

Answer 17

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

Question 18

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

Answer 18

impingement baffles

Question 19

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

Answer 19

longitudinal baffles

Question 20

what determines the number of tube side passes?

Answer 20

the number of baffles in the channel head

Question 21

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

Answer 21

fixed tubesheet

Question 22

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

Answer 22

fixed tube exchanger

Question 23

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.

Answer 23

shell
tube

Question 24

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

Answer 24

allow for thermal expansion

Question 25

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

Answer 25

large clearance at the head end of the pull through type

Question 26

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

Answer 26

when the two fluids cannot mix

Question 27

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

Answer 27

they have increased velocity which increases the turbulence

Question 28

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

Answer 28

cleaning is needed

Question 29

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

Answer 29

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

Question 30

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

Answer 30

shell outside

Question 31

zinc anodes are used to control _____________ action

Answer 31

electrolytic

Question 32

longitudinal baffles are used to increase _______________ pass

Answer 32

shell side

Question 33

what are drift eliminators in cooling towers used for?

Answer 33

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

Question 34

fins transfer heat from the tube by _______________

Answer 34

conduction

Question 35

list three purposes for segmental baffles

Answer 35

support the tubes cause turbulence prevent dead by-pass areas