Shell and Tube Heat Exchanger
1. Basic Definition
A Shell and Tube Heat Exchanger (STHE) is a classic and versatile type of heat exchanger consisting of a shell (a large pressure vessel) with a bundle of tubes inside it. One fluid runs through the tubes (tube side), and another fluid flows over the tubes (within the shell) to transfer heat between the two fluids.
2. Key Components
- Shell: The outer cylindrical vessel that houses the tube bundle. One fluid flows through the shell.
- Tube Bundle: A series of tubes enclosed within the shell. The second fluid flows through these tubes.
- Tube Sheets: Thick plates at both ends where the tubes are fixed. They separate the shell and tube side fluids.
- Baffles: Perforated plates placed inside the shell. Their key functions are:
- To support the tubes and prevent vibration.
- To direct the shell-side fluid across the tube bundle (increases turbulence and heat transfer efficiency).
- Front Head / Inlet Header: The part where the tube-side fluid enters the exchanger.
- Rear Head / Outlet Header: The part where the tube-side fluid exits. Its design allows for thermal expansion.
- Nozzles: Inlet and outlet ports for the shell-side and tube-side fluids.
3. Working Principle
Heat is transferred from the hot fluid to the cold fluid through the tube walls. The large surface area provided by the tube bundle facilitates efficient heat transfer. The fluids are kept separate, so they do not mix.
4. Common Flow Arrangements
- Counter-Flow: Fluids flow in opposite directions. This is the most efficient arrangement, providing the highest log mean temperature difference (LMTD).
- Parallel-Flow: Fluids flow in the same direction. Less efficient than counter-flow.
- Cross-Flow: Fluids flow perpendicular to each other (common with finned tubes).
5. Advantages
- High Pressure & Temperature Handling: Suitable for very high pressures and temperatures on the tube side.
- Robust Construction: Simple and strong design, known for reliability.
- Large Surface Area: Can be designed for very large heat transfer duties.
- Easy Maintenance: The tube bundle can be removed for cleaning and repair (a feature of “pull-through” baffle designs).
- Great Flexibility: Can be used for a wide variety of fluids (liquids, gases, condensing vapours) and applications.
6. Common Applications
- Power Plants: Condensers and feedwater heaters.
- Oil Refineries & Chemical Plants: For cooling process streams, condensing vapours, and preheating feeds.
- HVAC Systems: As chillers or for district heating.
- Marine Industry: As oil coolers for engines.
- Food and Beverage Processing.