Contents |
Summary
Fixed Tube
- Advantages
- Typically are least expensive
- Less Gaskets than other types
- Tubes are individually replaceable
- Disadvantages
- Shell is not able to be easily cleaned or inspected
- Maximum temperature difference between fluids is approximately 200oF with out the inclusion of an expansion joint.
- Notes
- Is used for clean shell fluids and low delta temperature.
- Large Diameter and High Pressure heads are designated usually BxM (Bonnet (Integral Cover) with a Fixed Tubesheet - for a Bonnet)
- Most commonly are designated as AxL. (Channel and Removable Cover with a Fixed Tubesheet Stationary Head)
Floating Head
- Advantages
- Ability to handle dirty fluids and high differential temperatures
- Both head and tubes can be cleaned.
- Individual tubes can be removed and replaced
- Disadvantages
- Cost more than fixed tube heat exchangers
- More gaskets than fixed tube heat exchangers which can cause leakage.
- Notes
- xTW (Cross Flow with a Pull Through Floating Head) are the least expensive but also have the highest possibility of leakage
U-Tube
- Advantages
- Lower cost than a fixed tub or floating head type echanger
- Desisn inherently allows for thermal expansion
- Internal gasketed joint is eliminated.
- Tube bundle is removable and replaceable
- Disadvantages
- Design does not allow for tubes to be mechanically cleaned
- The U Shaped tubes reduce the number of tubes that can be installed
- Individual tubes are not replaceable
- Notes
- U-Tube heat exchangers are used for high differential temperatures
- Usually these exchangers are used for "clean" service
Fluid Location
Tubes
Fluids should be put in the tubes (rather than the shell) if the fluid is:
- Under High Pressures
- Two Phase fluids or single phase gas
- Fluid has a tendency to scale. This is because it is easier to mechanically clean tubes on the inside rather than the outside.
Shell
Fluids should be put in the shell if the process requires:
- Low Pressure Drop
- Viscous heat transfer fluids
- Fluid is not sandy or fouling
- Low pressures
TEMA Designation
TEMA (Tubular Exchanger Manufacturers Association) has devised a standard nomenclature to briefly describe heat exchangers. The following is a description of the designation.
First Letter
| TEMA # | Description | Example |
|---|---|---|
| A | Channel and Removable Cover | 
|
| B | Bonnet (Integral Cover) | 
|
| D | High Pressure Closure | 
|
| N | Channel Integral with Tubesheet & Removable Cover | 
|
Second Letter
| TEMA # | Description | Example |
|---|---|---|
| E | One Pass Shell | 
|
| F | Two Pass Shell with Longtidudinal Baffle | 
|
| G | Split Flow | 
|
| H | Double Split Flow | 
|
| J | Divided Flow | 
|
| K | Kettle Type Reboiler | 
|
| X | Cross Flow | 
|
Third Letter
| TEMA # | Description | Example |
|---|---|---|
| L | Fixed Tubesheet Stationary Hea | 
|
| M | Fixed Tubesheet - Bonnet | 
|
| N | Fixed Tube Sheet Channel Integral with Tube Sheet & Removable Cover | 
|
| P | Outside Packed Floating Head | 
|
| S | Floating Head with Backign Device | 
|
| T | Pull Through Floating Head | 
|
| U | U-Tube Bundle | 
|
| W | Externally Sealed Floating Tubesheet | 
|
Design Considerations
Shell and tube heat exchangers should be located to facilitate the ease of tube removal for cleaning and maintenance.
When the tube bundles are withdrawn, they should not project into an emergency escape route or any road with unrestricted vehicle access.
The spacing between heat exchanger shells must allow for sufficient, unobstructed clearance for access for the bundle withdrawal equipment and to permit access for shell flange gasket replacement (when applicable).
