Shell & tube heat exchangers are very popular and commonly found in industrial use. This is mainly due to their versatility. A shell and tube exchanger consists of a shell, tube bundle and two heads or caps at both ends of the shell. By selecting different configurations of these basic parts, we can have many different exchanger types as per TEMA.
Design of a shell & tube exchanger is governed by standards provided by TEMA (Tubular Exchangers Manufacturers Association).
As per the TEMA standards, there are 3 important parts for shell & tube exchanger design.
- The front end
- Rear end
Different configurations of these 3 parts result in different exchanger types as per TEMA. Following table from the TEMA standards explains the different possible configurations for each of the 3 broad parts.
Other smaller parts are listed in this detailed diagram of a shell & tube heat exchanger, along with their correct nomenclature as per the TEMA standards.
Shell & Tube Heat Exchanger Types
Many different exchanger configurations can be easily created by different combinations of front end, shell and rear end. Moreover depending on how tube bundle is fixed to the front end or rear end cover, we have 3 broad types of shell & tube heat exchanger construction.
Fixed Tubesheet Exchanger
A fixed-tubesheet heat exchanger has straight tubes that are secured at both ends to tubesheets welded to the shell.
The main advantage of the fixed tubesheet exchanger is its low cost because of its simple construction. Fixed tubesheet being the least expensive shell & tube exchanger type, as long as we don't use any expansion joint.
But for the same reason, fixed tubesheet exchanger does not help much for services having large temperature difference between shell & tube sides. Because in such cases, an expansion joint would be needed.
Other advantages are that the tubes can be cleaned easily by removing the channel cover or bonnet. Moreover, absence of flanged joints helps to minimize the leakage of the shellside fluid.
But there is a disadvantage that the outsides of the tubes cannot be cleaned mechanically, as the tube bundle is fixed to the shell. Fixed tubesheet exchangers require that a clean fluid must be used on the shell side.
When you have a dirty fluid on tube side, you may consider this type of exchanger.
U tube exchanger
As the name suggests, in this type the tube bundle is U shaped. There is only one tube sheet. All the tubes start from upper half of this tubesheet, make a U turn in the shell and come back to the lower half of the same tube sheet. As shown in the following diagram.
The advantage of using a U tube bundle is that the tubes can freely expand as they are U turn end of the bundle is freely floating in the shell side. Hence a U tube exchanger is the preferred option where there is high temperature difference between shell & tube side fluids and tube expansion is expected.
But as the same time, this U shape of the tubes makes it difficult to mechanically clean them. Only chemical cleaning would be possible. Hence U tube exchangers are normally not preferred where we need to use a dirty or fouling service on the tube side.
These exchangers are also cost effective, as expansion joints are not needed and tube tube bundle is free to expand.
Floating head exchanger
Thanks to this design, this type of shell & tube heat exchangers can withstand fluids to high temperature difference, as the tubes are free to expand. Also, the floating head cover can be easily removed to mechanically clean insides of the tubes. Therefore even dirty and fouling services can also be used on the tube side.
That makes this shell & tube heat exchanger type most versatile in terms of its applicability to different scenarios.
But the design is quite complex, making it also the most expensive type of shell & tube exchangers.
TEMA Type Nomenclature
Further, there are multiple types of shell, front end cover and rear end cover. The final heat exchanger configuration will depend on what we select.
For example, an AEL type shell & tube exchanger will consist of -
- Removable front end cover "A"
- One pass shell "E"
- Fixed tubesheet rear end cover "L" (like "A")
A, E and L are explained in the table from TEMA standards above.
Shell & tube heat exchanger types based on service
We may have two fluids in the shell and tube exchanger on both - shell side and tube side. That leads to multiple combination of services -
- single-phase (both shellside and tubeside)
- condensing (one side condensing and the other single-phase)
- vaporizing (one side vaporizing and the other side single-phase)
- condensing/vaporizing (one side condensing and the other side vaporizing)