1. Heat Exchanger & Classification Prepared by: Nimesh Gajjar
Introduction to
Heat Exchanger & Classification
Prepared by: Nimesh Gajjar

2. HEAT EXCHANGERS
Device that facilitates the exchange of heat between two fluids that are at different temperatures without mixing each other
Heat transfer in a heat exchanger involves
Convection in each fluid
Conduction through wall separating each fluid
Overall heat transfer co efficient accounts for the above
Conduction and convection effects
Hot Fluid
Cold Fluid
Convection
Conduction

3. Applications of Heat Exchangers
Heat Exchangers prevent car engine overheating and increase efficiency
Heat exchangers are used in Industry for heat transfer
Car—prevent overheating with “high performance cooling applications”
Maintain fluids at optimal temperature such that engine efficiency is increased and component wear minimized
Boilers and condensers are opposite processes used in industry
-Boilers used to create steam—sometimes to drive steam driven turbines
-condenseros bring steam back to liquid for reuse
Distillation set-ups typically use condensers to condense distillate vapors back into liquid.
Ultimately, condensers-cool refrigerant vapor back to liquid-- sub cooled liquid flows out of the condenser and into the evaporator where it absorbs heat from air in the surrounding pipe and generates cold air.
Air conditioners utilize a closed heat exchange system that separates the hot and the cold fluids. Energy is transported via convection between the fluid and inner pipe surface, conduction through the pipe and then convection from the outer pipe surface into the second fluid. This closed system is very similar to the one examined in this lab experiment, and its widespread applicability is why this lab was designed.
Heat exchangers are used in AC and furnaces

4. Classification of Heat Exchangers
These are most common heat exchangers in which hot and cold fluid do not come into contact with each other but are separated by a tube wall or a surface which may be flat or curved .
Energy exchange by hot fluid to surface by convection through the wall or plate by conduction and then by convection from the surface to the cold fluid.
They are used where mixing of hot and cold fluid is objectionable. For eg. Oil coolers, intercoolers, air preheaters, economisers, condensers. 2) radiators of automobiles 3) evaporator of an ice plant and milk chiller of a pasteurizing plant

5. These are heat exchangers in which hot and cold fluids flow alternatively ( i.e. periodically) through the same space with no or little physical mixing between the streams.
The heat carried away is accumulated in the walls of the equipment called solid matrix and is then transferred to the cold fluid when it passes the surface next.
Mostly used in gas to gas heat exchangers such as IC engines and gas turbines.
Other applications in glass melting furnace and air heaters of blast furnace.
Depending Parameters-1) heat capacity of regenerating material
2)rate of absorption and release of heat

7. According to Construction :
Tubular heat exchanger (double pipe, shall and tube, coiled tube) TubularHeatEx.swf TripleTubeHe.swf shelltubehex.swf
Plate heat exchanger ( spiral, plate coil, lamella) PlateHeatEx.swf
Extended surface exchangers (tube fin, plate fin)
Regenerators (fixed matrix, rotary)

8. PLATE HEAT EXCHANGER
Spiral Plate HE Lamella Plate HE

9. SHELL AND TUBE HEAT EXCHANGER
Rear-end
header
Shell outlet
Tube inlet
Tube outlet
Shell inlet
Shell
Baffles
Tubes
Front-end
Compact heat exchanger
Gas to gas HE
Gas to liquid or liquid to gas HE
Low heat transfer coefficient on gas side – Increase surface area using fin

10. According to Transfer Process
1) Indirect Contact
(double pipe, shall and tube, coiled tube)
2) Direct contact
(cooling towers)

11. COMPACT HEAT EXCHANGERS
β >700 m2/m3 –Compact
Car radiator β =1000 m2/m3
Gas turbine HE β =1000 m2/m3
Human lungs β =20000 m2/m3
Achieve high heat transfer rates between two fluids in a small Volume
The ratio of the heat transfer surface area of a heat exchanger to its volume is called the “area density β’’.
A heat exchanger with area density β is greater than 700 m2/m3 or 200 ft2/ft3 is classified as being compact.

12. According to Flow Arrangement
Concurrent – Flow in same direction
Thermodynamically poor
High thermal stresses since large temperature difference at inlet
Heat sensitive materials
TubularHeatEx.swf
Counter current- flow opposite to each other
Thermodynamically superior
Minimum thermal stresses
Maximum heat recovery
Least heat transfer area
Cross flow- Flow perpendicular to each other
In between the above
Design of headers require less space

13. b) One fluids mixed, one fluid unmixed
CROSS FLOW HEAT EXCHANGER
Cross-flow
(mixed)
Tube flow
(unmixed)
b) One fluids mixed, one fluid unmixed
Cross-flow
(unmixed)
Tube flow
a) Both fluids unmixed

14. Double pipe heat exchanger:
Parallel Counter flow
Hot Fluid
Cold Fluid T
Hot fluid in
Hot fluid out
Cold fluid in
Cold fluid out
TubularHeatEx.swf

15. According to Pass Arrangement
Single Pass
Two Pass
Multi Pass

16. Two shell four tube pass
One shell two tube pass
Shell-side fluid In
Tube-side fluid
Out
Tube-side fluid
Shell-side fluid In
Out
Two shell four tube pass

17. According to Phase of Fluid: According to Mechanism of Heat Transfer
These classifications is made according to the phase of the fluid.
gas-gas,
liquid-liquid,
Gas-liquid etc.
According to Mechanism of Heat Transfer
Single phase convection, (forced or free).
Two phase convection (condensation or evaporation) by force or free convection .

18. According to Extended Surface:

19. Overall heat transfer coefficient
Ai – Inside area of the tube
Ao – Outside area of the tube
hi – inside heat transfer coefficient
ho – Outside heat transfer coefficient
k – thermal conductivity of tube
Cold fluid
Hot fluid
Wall
Heat transfer
U is meaningless unless area is specified