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Flashcards in Heat Exchangers Deck (20)
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1
Q

Conduction

A
  • heat transfer through a solid

- like the handle of a kettle becoming hot while the kettle is heating

2
Q

Convection

A
  • heat transfer through a liquid

- can not occur in a solid

3
Q

Radiation ( radiant heat)

A

-can transfer across a vacuum or a gas

4
Q

Gas(air) to gas(air)

A

-commonly used in compressors with intercoolers and after coolers

5
Q

Liquid to gas

A
6
Q

Liquid to liquid

A

-both sides of the tubes have liquid flowing through

7
Q

Three types of heaters

A

-

8
Q

Type of flow paths

A

-parallel, counter, cross flow, mixed flow

9
Q

Type of exchangers

A

-

10
Q

-parallel flow

A
  • both fluids flowing in the same direction

- 2 fluids reach equilibrium at the halfway point between the two temperature extremes

11
Q

Counter flow

A
  • most efficient

- can reach the two temperature extremes if given enough time

12
Q

Cross flow

A

-can produce lots of turbulence which makes for greater efficiency for a given size exchanger

13
Q

Mixed flow

A

-common in heat exchangers with baffles that cause the flows to switch between parallel and counterflow

14
Q

Finned tube exchanger (radiator)

A
  • most common exchanger as it is a car radiator

- fins are added to increase surface that in turns transfers more heat

15
Q

Plate heat exchanger

A
  • high turbidity
  • a number of pressed metal plates clamped together on a frame with gaskets. The fluid flows between the plates
  • great for heat transfer because of the amount of surface area
  • can’t Handle high pressure because of the gaskets between the plates
16
Q

Spiral heat exchanger

A
  • uses counterflow which helps make it the most efficient and has many spirals inside it which creates turbulence.
  • also has lots of surface area because of the spirals.
17
Q

Natural or mechanical draft Cooling towers

A
  • natural relies on wind conditions
  • mechanical use induced or forced draft just like fans. They have mist eliminators that help collect the water in the airstream
18
Q

Double pipe heat exchanger

A
  • uses counter current flow and because of the piping it can be used for high pressure
  • these can be hooked together in series on a wall and take up very little space
  • most common is the hairpin because it can handle differential thermal expansion
19
Q

Shell & Tube baffles

A
  • segmental - drilled plates equally spaced causing the fluid to flow back and forth across the tubes
  • disc & doughnut - has a relatively smooth flow
  • impingement - reduce erosion by entering fluid
  • longitudinal - used to split the shell side flow into two or more passes
    - 3 longitudinal baffles make a 4 pass shell
20
Q

Baffle Main functions

A

-support the tubes and create turbulence to increase heat transfer