1. CLASSIFICATION OF HEAT EXCHANGERS
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CLASSIFICATION OF HEAT EXCHANGERS
BE Sem- 5 Heat Transfer ( )
PREPARED BY: GROUP NO. 17
BHANA ABUBKAR S.
PATEL JAYKUMAR N.
PATEL KALPESHKUMAR H.
PATEL KUNALKUMAR K.
PATEL PARTHKUMAR N.
MECHANICAL ENGINEERING DEPARTMENT
GOVERNMENT ENGINEERING COLLEGE,
DAHOD

2. HEAT EXCHANGER:
A Heat Exchanger may be defined as a Mechanical device which transfer the heat from hot fluid to cold fluid, with maximum rate, with minimum investment and with running cost.
Notable examples are:
Boilers, super heater and reheaters,
Radiators of automobiles,
Oil coolers of heat engine,
Evaporator and condensor of refrigeration system ,
Regenerator of gas turbine power plants,
Water and air coolers or heaters,
Several other industrial processes.

3. Classification of Heat Exchangers:
Many types of heat exchangers have been developed to meet the widely varying applications which are classification based on :
Operating principle ( nature of heat exchanger process),
Relative direction of fluid motion,
Design and constructional features,
Physical state of fluid , etc.

4. A) According to operating principle heat transfer process:
According to heat exchange process
Non Direct contact type of heat exchanger
Recuperator
Examples:
1.Radiator
2.Oil heaters etc.
Regeneration
examples:
1.Open hearth furnace
2.Glass melting furnace etc.
Direct contact type of heat exchanger
1.cooling tower
2.condensor etc.

5. A1) Direct contact type heat exchanger:
In direct contact type or open type of heat exchangers the heat transfer take place between two fluids by direct contact between them.
There is simultaneous transfer of heat and mass refer fig. 1
The rate of heat transfer is maximum in such case.
The use of direct contact type heat exchanger is limited to the situation where mixing between the fluids is either desirable or harmless.

7. A2) Non – contact type of heat exchangers:
In indirect or non-contact type of heat exchanger ,the direct heat exchange between two fluids is not possible as there is no direct contact between two fluids.
This type includes regenerators
And recoperators.
Regenerators: refer fig. no.2
Hot fluid is passed through a
Certain medium called matrix.
The hot fluids is passing through
One sides of matrix, stored in
Matrix and given to cold fluid by
Rotation of matrix from hot to
Cold fluid side.
Operation of regenerators is periodic and some mixing of two fluid is possible.
It gives quick response to load variation, minimum pressure losses and quite high efficiency.

8. Recuperators : Refer fig. no. 3
In recuperator, the fluids flow simultaneously on either side of separating wall.
The heat transfer occurs between the fluids streams without physical contact or mixing with each other.
It is suitable for stationary plants, having more area for heat transfer, cheaper in cost and easy in construction.
But the rate of heat transfer is less and have cooling problems.

9. B)According to the direction of fluid motion
Parallel flow or unidirectional flow or concurrent flow
Examples:
1.Oil coolers
2. Oil heaters
3.Water heaters
Counter flow or counter current flow
1. Used almost in all engineering application
Cross flow
1.Cooling units of refrigeration system
2.Automobile radiator

10. B1)Parallel flow/unidirectional flow:
In case of parallel floe heat exchanger, both the fluids are flowing in the same directions.
Fig.4 represented the variations in temperature along the length of heat exchanger.
Since this type of heat exchanger needs a large area of heat transfer, therefore , it is rarely used in practice.
As the two fluids are separated by a wall, this type of heat exchanger may be called parallel flow recuperator.

11. B2) Counter flow/ Counter current heat exchanger:
In case of counter flow heat exchanger , both the fluids are flowing in the opposite directions.
The arrangement and temperatures variations along the length of heat exchange for such heat exchangers are shown in fig.

12. B3)Cross flow heat exchanger:
Fig. shows schematic diagrams of common arrangements of cross flow heat exchangers, both fluids are directed at right angles to each others.
Fig.(a) represents the case in which there is no mixing of fluids streams which is flowing over the tube(i.e. example: automobile radiator).

13. Fig(b) represent the mixing of fluid streams at one side (i. e
Fig(b) represent the mixing of fluid streams at one side (i.e. over tubes) (Example : condensor of refrigerating system , where air stream will mix together and refrigerent stream does not mix).

14. C) Mechanical design of heat exchanger surface
It is classified as given below:
Concentric tube type heat exchangers,
Shell and tube,
Multiple shell and tube passes,
Compact heat exchangers,
Finned tube type

15. C1)Concentric tube type heat exchangers:
Fig. represents concentric tube type of heat exchanger.
These are also called tubular heat exchangers or tube in tube type of heat exchangers or double pipe heat exchanger.

16. C2) Shell and tube type heat exchangers:
These are also called surface condensor.
In shell and tube type heat exchangers, one fluid with flow through shell and other will flow through tube.
There is no direct contact between two fluids and the heat will transfer.

17. A typical exchanger is shown in fig.
Multiple shell and tube passes are used for enhancing the overall heat transfer area.
Multiple type pass heat exchangers are those which re route the fluid through tubes in opposite direction.
Examples are surface condensor in thermal power plants

18. C3) Compact heat exchangers
These are special type of heat exchangers in which heat transfer surface area per unit volume is very large.
They are generally employed when convective heat transfer associated with one of the fluids is much smaller than that of associated with the other fluids.
These are usually cross floe heat exchangers. .

19. C4) FINNED TUBE TYPE HEAT EXCHANGERS:
When very high rate of heat transfer is required, fins are placed on the one side of heat exchanger which is called finned tube type of heat exchangers.
The use of fins enhance heat transfer area and thereby heat exchanges.
These heat exchangers are in IC engine cylinder, Gas turbines, refrigerators, electronics equipments, air conditioning systems etc., radiator of an automobiles is a example of said heat exchanger.

20. D) Physical state of fluids
Condensors
Evaporators :

21. D1) Condensors:
In condensors, the temperature of hot fluid remains same for the entire length of the heat exchanger but the temperature of cold fluid increases gradually along the length of heat exchanger.
Refer fig.
The hot fluid reject latent heat which is absorbed by the cold fluid.
In case of condensor of thermal power plant, the hot fluid is steam and the cold fluid is cooling water which is gaining the heat and rejecting the heat in cooling towers.
Fig. Temperature distribution for condensor

22. D2)Evaporators:
In evaporators, the temperature of cold fluid remains same and the hot fluid temperature drops.
The cold fluids receives latent heat from the hot fluid.
In case of thermal power plants, the flue gases(hot fluids) reject the heat and the heat and the same is gain by the cold fluid (i.e. water ) in boilers.
Fig. Temperature distribution for evaporator

23. Reference:
Heat Transfer by Prof. ALPESH V. MEHTA & Prof. PINKAL G. CHOKSI, Book Of India
Heat and Mass Transfer by R K RAJPUT, S. CHAND PUBLICATION

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