1. Heat exchangers
The device at which heat exchange between two fluids at different temperatures and separated by a solid wall occurs is called heat exchanger.
Its applications may be found in space heating, air conditioning, power production, waste heat recovery and chemical processing.

4. The principle Types of heat exchangers
Double pipe heat exchangers
Shell and tube heat exchangers
Plate and frame heat exchangers
plate fin heat exchangers
Air cooled heat exchangers
Spiral heat exchangers
Fired heaters [boilers]

5. 1-Double pipe heat exchanger
Construction

6. 1-Double pipe heat exchanger
Hairpin unit

7. Flow patterns
1-Co current flow [parallel flow]

8. 2- counter current flow

9. 3-Cross flow
Intermediate effectiveness between parallel flow and couterflow exchangers. [not used with double pipe]

10. 2-Shell and tube heat exchanger
The most common used type….why?
The configuration gives a large surface area in a small volume (i.e. compact)
Can be constructed from a wide range of materials
Well established design procedure

11. 2-Shell and tube heat exchanger
Types of shell and tube heat exchangers:
Fixed tube sheet (plate)
U- tube
Internal floating head without clamp ring
Internal floating head with clamp ring
External floating head
Kettle re-boiler with U- tube bundle

12. Fixed tube sheet (plate) H.X
Main components

13. Fixed tube sheet (plate) H.X

14. F E G H J X Shell types[ passes] Two shell pass One shell pass
Shell side flow arrangements are generally one of the following illustrated F E
Two shell pass
One shell pass G H
Longitudinal
baffles
Split flow
Double split flow J X
Divided flow
Cross flow

15. Example
Split flow type

16. Factors affecting the choice of the shell arrangements
The amount of cooling and heating required
The pressure drop
The type of service [for instance the shell arrangement that provides space for vapors to accumulate is the kettle type re-boiler

17. Kettle type Re-boiler

18. Baffles Why are baffles used? To support the tube
To direct the fluid stream across the tube
To improve the rate of heat transfer
Shell
Tubes
Baffle

21. U-tube heat exchanger or U bend exchanger

23. Isometric view for U-tube exchanger

24. When to use this type?
It is used where the temperature difference between the shell side and tube side fluids is quite great….WHY?
Because the tubes are free to expand since the tube bundle is fastened to only one tube sheet.

25. Internal floating head without clamp ring

26. Internal floating head with clamp ring

28. Allocation of fluids Tube side
Put dirty stream on the tube side [fouling fluid] - easier to clean inside the tubes
Put high pressure stream in the tubes to avoid thick, expensive shell
When special materials required for one stream, put that one in the tubes to avoid expensive shell
Put corrosive fluid in the tube tom reduce the cost of expensive shell
Put toxic fluid in the tube to minimize leakage

29. Shell-Side
1. Viscous fluid to increase (generally) the value of "U“ [Cross flow gives higher coefficients than in plane tubes, hence put fluid with lowest coefficient on the shell side]
2. Fluid having the lowest flow rate
3. Condensing or boiling fluid
Note
If no obvious benefit, try streams both ways and see which gives best design

30. Heat exchangers problems
Exchanger fouling
Corrosion
vibration

31. Build up of various kinds of deposits on the parts of an exchanger
Definition of fouling
Build up of various kinds of deposits on the parts of an exchanger
Types of fouling
Salt deposit [as Ca and Mg deposits in case of hard water]
Chemical fouling [as corrosion products]
Biological fouling [as growth of algae which form insulating layer]
Coking

32. Effect of fouling on the H.X performance
Increase the thermal resistance and reduce the rate of heat transfer [decrease the efficiency of the H.X]
Increase the surface roughness [the flow of the fluid is restricted] and increase the pressure drop
Troubles that indicate the presence of fouling
Change in temperature or pressure
Change in flowrate [outlet flow rate]

33. Factors affecting the kind and degree of fouling
The materials used in the heat exchanger
Some materials corrode faster than others providing corrosion products which decrease heat transfer
Rough surface provides cavities for the build up of deposits
Fluid velocity
Affect the fouling rate [as the velocity increase the fouling rate decrease]

34. How to handle the problem of fouling
Antifoulants prevent the formation of deposits
Inhibitors [as corrosion inhibitors] prevent chemical reactions
which might cause deposits to build up
Frequent cleaning of the H.X [maintenance]

35. Corrosion of heat exchangers
Another series problem in heat exchangers is corrosion
Severe corrosion can and does occur in tubing and very often with
common fluids such as water
To avoid corrosion
Proper material selection based on full analysis of the operating fluids, velocities and temperatures is a must
Heavier gauge tubing is specified to offset the effect of corrosion followed by proper start up operating and shut down procedure
Protection of the heat exchanger from corrosion [e.g.cathodic protection]
Treatment of the cooling water used and using inhibitors

37. Heat exchangers vibration
Vibration of the tubes as a result of the flow of the shell side past them is important phenomena specially when the H.X size and flow quantities of flow are increased
Vibration effects
Vibration has a bad effect on both tubes and shell
The joints between the tubes and tube sheet can fail due to vibration causing leakage
It causes leakage in the joints between shell and tubes
Increase the shut down time to repair the H.X

38. Factors affecting tube vibration
Tubes geometry [layout]
Material of construction
Means of support
Heat exchanger size
Flow quantities

39. How to avoid vibration Using inlet support baffles
Using double segmental baffles [improve tube support]
Using j shell type [ divided flow type to reduce the shell velocity]
Inlet support
baffles
Double-segmental baffles

40. Air cooled heat exchanger
Used for cooling and condensation and used when cooling water is in short supply or expensive
They can also be competitive with water cooled units even when water is plentiful
Most common used in petroleum and gas processing industries
Main components
Air cooled exchangers consist of banks of finned tubes over which air is blown or drawn by fans mounted below or above the tube
If the fan is mounted below the tubes the unit is termed forced draft unit and if the fan is mounted above the tubes the unit is termed induced daft

41. Forced draft air cooled heat exchanger
[cross flow]

43. Spiral heat exchanger

46. Flow patterns in plate heat exchanger