What is Shell and Tube Heat Exchanger (STHE)?
What is a Shell and Tube Heat Exchanger (STHE)?
A Shell and Tube Heat Exchanger (STHE) is a class of heat exchanger design and the most common type used in various industrial applications. It is built around a shell (a large pressure vessel) with a bundle of tubes inside it.
Core Principle: One fluid runs through the tubes (the tube side), and another fluid flows over the tubes (within the shell but outside the tubes, known as the shell side). Heat is transferred from the hotter fluid to the colder fluid through the tube walls.
Key Components and Their Functions
To understand an STHE, it’s best to break it down into its main parts:
- Shell: A large cylindrical pressure vessel that houses the tube bundle. It has inlet and outlet nozzles for the shell-side fluid.
- Tube Bundle: The heart of the exchanger. It consists of:
- Tubes: The primary heat transfer surface. They can be made of various metals (e.g., stainless steel, copper, titanium) depending on the fluids and pressures involved.
- Tube Sheets: Thick plates, usually at both ends of the shell, into which the tubes are securely fastened (often expanded or welded). They create a pressure boundary between the shell and tube sides.
- Baffles: Perforated plates placed inside the shell. Their key functions are:
- To support the tubes and prevent vibration.
- To direct the shell-side fluid flow across the tube bundle (in a zig-zag pattern), increasing turbulence and improving heat transfer efficiency.
- Channels / Heads: These are attached to the tube sheets and control the flow of the tube-side fluid into and out of the tubes. Different types of heads allow for different flow patterns:
- Front Head: Where the tube-side fluid enters.
- Rear Head: Where the tube-side fluid exits. The type of rear head determines how many “passes” the fluid makes.
- Nozzles: Inlet and outlet ports for both the shell-side and tube-side fluids.
Common Types and Classifications
STHEs are highly versatile and can be classified based on their service or construction:
- Based on Service:
- Heater: Uses a hot fluid to heat a cooler fluid.
- Cooler: Uses a cold fluid to cool a hotter fluid.
- Condenser: Condenses a vapor into a liquid by removing latent heat.
- Chiller: Uses a refrigerant to cool a fluid to a temperature below the ambient level.
- Boiler / Vaporizer: Heats a liquid to its boiling point to create vapor.
- Based on Construction (primarily the rear head):
- Fixed Tube Sheet: The tube sheet is welded directly to the shell. It is the simplest and cheapest design but cannot be cleaned mechanically on the shell side. Used for clean fluids.
- U-Tube: The tubes are bent into a U-shape, allowing both ends to be connected to a single tube sheet. The bundle can expand and contract freely with temperature changes (thermal expansion) and can be removed for cleaning. However, the inside of the U-bends can be difficult to clean.
- Floating Head: One tube sheet is fixed, and the other is allowed to “float” within the shell. This is the most versatile design, accommodating thermal expansion and allowing the entire bundle to be removed for cleaning on both sides. It is also the most complex and expensive.
Advantages and Disadvantages
| Advantage | Disadvantage |
| High Pressure Handling: Excellent for high-pressure applications (the fluid inside the tubes can be under very high pressure). | High Cost: Generally, more expensive than plate or air-cooled heat exchangers for the same duty. |
| Robust Construction: Durable and can withstand harsh operating conditions. | Large Footprint: Bulky and takes up significant space compared to compact designs like plate heat exchangers. |
| Easily Cleaned (Floating Head/U-Tube): The tube side is easy to clean mechanically. The bundle can be removed for shell-side cleaning. | Less Efficient: Lower heat transfer efficiency per unit volume due to lower turbulence and surface area compared to plate heat exchangers. |
| Great Design Flexibility: Can be designed for a vast range of temperatures, pressures, and duties by changing materials, tube length, diameter, and count. | Fouling: Baffles create dead zones where fouling (deposit build-up) can occur on the shell side. |
| Well-Understood Technology: A mature, proven design with established standards (e.g., TEMA standards). |
Common Applications
Due to their robustness and flexibility, STHEs are ubiquitous in industry:
- Power Generation: Condensing steam from turbines.
- Oil & Gas Refineries: Cooling process streams, condensing hydrocarbons, and pre-heating crude oil.
- Chemical and Petrochemical Plants: Precise temperature control for chemical reactions.
- HVAC Systems: As chillers for large building cooling systems.
- Marine Industry: Cooling engine jacket water with seawater.
- Food and Beverage Processing: Pasteurization and sterilization processes.