Heat Exchangers

Question 1

Conduction

Answer 1

• heat transfer through a solid

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

Question 2

Convection

Answer 2

• heat transfer through a liquid

- can not occur in a solid

Question 3

Radiation ( radiant heat)

Answer 3

-can transfer across a vacuum or a gas

Question 4

Gas(air) to gas(air)

Answer 4

-commonly used in compressors with intercoolers and after coolers

Question 5

Liquid to gas

Question 6

Liquid to liquid

Answer 6

-both sides of the tubes have liquid flowing through

Question 7

Three types of heaters

Answer 7

-

Question 8

Type of flow paths

Answer 8

-parallel, counter, cross flow, mixed flow

Question 9

Type of exchangers

Answer 9

-

Question 10

-parallel flow

Answer 10

• both fluids flowing in the same direction

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

Question 11

Counter flow

Answer 11

• most efficient

- can reach the two temperature extremes if given enough time

Question 12

Cross flow

Answer 12

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

Question 13

Mixed flow

Answer 13

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

Question 14

Finned tube exchanger (radiator)

Answer 14

• most common exchanger as it is a car radiator

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

Question 15

Plate heat exchanger

Answer 15

• 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

Question 16

Spiral heat exchanger

Answer 16

• 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.

Question 17

Natural or mechanical draft Cooling towers

Answer 17

• 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

Question 18

Double pipe heat exchanger

Answer 18

• 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

Question 19

Shell & Tube baffles

Answer 19

• 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

Question 20

Baffle Main functions

Answer 20

-support the tubes and create turbulence to increase heat transfer