Shell and Tube Heat Exchanger
United Heat Exchangers’ Shell and Tube Heat Exchanger delivers a robust, high-performance solution for industrial and commercial heat transfer needs. Its proven design features a bundle of tubes enclosed in a cylindrical shell, enabling two fluids to exchange heat efficiently. This construction offers exceptional flexibility: it can handle a wide range of pressures and temperatures (as noted by industry guidelines). In fact, most process-plant shell-and-tube units are built to TEMA standards (Tubular Exchanger Manufacturers Association) to meet severe-service requirements. With customizable materials and configurations, United’s exchangers excel in demanding settings like oil & gas refineries, power plants, HVAC systems, and chemical processing.
Key Features
- Durable Construction: Engineered for longevity under heavy-duty conditions. The shell and tubes are available in carbon steel, stainless steel (304/316), copper alloys, or high-performance alloys like titanium. These materials are chosen for strength, thermal conductivity, and corrosion resistance. For example, carbon steel provides a cost-effective shell in non-corrosive services, while 316 stainless steel tubing resists corrosive chemicals.
- Efficient Heat Transfer: The multi-tube bundle provides a large transfer area in a compact unit. Internal baffles direct the shell-side flow across the tubes, creating turbulence and maximizing heat exchange. This baffle-guided flow both boosts heat transfer and supports the tubes against vibration.
- Flexible Flow Arrangements: Designed for counter-current or co-current flow. Counter-current flow (fluids moving in opposite directions) yields the highest thermal efficiency, allowing the cold fluid to exit nearly as hot as the hot fluid’s inlet temperature. United’s exchangers can be configured with multiple tube passes and shell passes (e.g., 1-shell 2-tube-pass or more) to tailor the temperature approach and pressure drop to your process.
- Multiple Configuration Options: Three basic styles are offered: fixed tube sheet, U-tube, and floating head designs. In fixed-tube sheet units, the tube sheet is welded to the shell (simple and economical), though only the inside of tubes is easily cleaned. U-tube bundles are bent back on themselves, allowing unlimited thermal expansion and easy tube-side cleaning. Floating-head types let the bundle slide out for full cleaning and expansion, ideal for very high temperatures and pressures. (See TEMA nomenclature for more details on header and shell types.)
- High Pressure and Temperature Ratings: Built to TEMA Classes R, C, or B, as required. Class R construction (refinery) is heavier-duty for petroleum service, while Class C is for general commercial use and B for chemical service. With thick shell walls and robust flanges, these exchangers handle high design pressures (often 10–20 MPa) and hot fluids up to hundreds of °C. The floating-head and U-tube designs accommodate differential expansion, making them suitable for thermal cycles without stress.
- Customizable Dimensions: Available in a range of diameters and lengths. For example, tube outside diameter is commonly 19.05 mm (3/4") in process applications. Typical tube lengths range from 2 to 6 meters (6–20 ft), and shell diameters from a few hundred millimeters up to over a meter, depending on flow requirements. United supplies units sized to your heat duty, flow rate, and space constraints.
- Easy Maintenance: Designed for serviceability. Units with U-tube or floating heads allow the tube bundle to be removed for cleaning or inspection. Additionally, compared to gasketed plate exchangers, most shell-and-tube units have welded construction with no internal gaskets to replace. When removable tubes use simple O-ring seals, repairs are straightforward. This means fewer maintenance shutdowns and lower lifetime service costs.
How It Works
Figure: Cross-sectional diagram of a U-tube shell-and-tube heat exchanger. The hot fluid (red arrows) flows through the U-shaped tubes, while the cold fluid (blue arrows) flows through the shell across the tubes. This counter-current flow maximizes heat transfer.
Shell-and-tube heat exchangers transfer heat between two fluids without mixing them. One fluid (for example, hot oil or steam) flows inside the tube bundle, and the other fluid (such as water or cooling air) flows around the tubes within the shell. Heat conducts through the thin metal walls of the tubes: the hotter fluid cools down while the colder fluid heats up. By arranging the inlet and outlet so that fluids flow in opposite directions (counter-current flow), the temperature difference is maintained along the length of the exchanger, maximizing efficiency.
Inside the shell, baffles force the shell-side fluid to zigzag across the tubes rather than flow straight through. This crossed flow increases turbulence and contact with the tube surfaces, improving heat transfer. The baffles also hold the tubes in place, reducing vibration and wear. Depending on the number of tube passes and baffle design, the unit can approximate counter-current flow. In practice, designers balance heat transfer needs with pressure drop and mechanical considerations when choosing flow paths and baffle spacing.
Materials and Construction
- Shell Material: Carbon steel is the standard choice for general service due to its strength and cost-effectiveness. For corrosive environments, the shell can be lined with inert materials or made of stainless steel or alloy steel.
- Tube Material: Tubes are commonly 304 or 316 stainless steel (good corrosion resistance and temperature performance). Copper or copper alloys (brass, Cu-Ni) are used when high thermal conductivity is needed (e.g., refrigeration). For extremely corrosive fluids, nickel alloys or titanium tubes are available.
- Tube Arrangement: Tubes are arranged in a triangular or square pitch to maximize density. The standard triangular (30°) pitch yields a compact design with a large surface area. Triangular layouts also help distribute shell-side flow for even heat transfer.
- Tube-Side Features: Tube sheets support the tubes on each end. When U-tubes are used, a single tube sheet can support both legs of each tube (saving cost). In fixed-head or floating-head designs, there are separate front and rear tube sheets. All welding and fabrication follows ASME pressure vessel codes for safety.
- Baffles and Inserts: By default, single-segmental baffles are used. If lower pressure drop or minimized vibration is needed, double-segmental or rod baffles can be specified. Specialized inserts (like twisted tapes or fins) can also be added to increase turbulence for very viscous fluids.
Configurations and Standards
United’s shell-and-tube exchangers are offered in standard TEMA configurations (e.g., AEL, BEM, AEU, etc.) depending on your needs. Examples of key design options:- Fixed Tube sheet (TEMA L/M/N-Type): Simple, leak-tight unit. Cannot mechanically clean the shell side (requires chemical cleaning only).
- U-Tube (TEMA U-Type): One end of the bundle is free. Allows the bundle to expand/contract with temperature and is removable for tube-side cleaning. (Disadvantage: only one tube sheet, so the shell-side can only be cleaned from one end.).
- Floating Head (TEMA S/T/P-Type): The rear (or front) end cover is removable. The bundle can be fully removed for cleaning on both sides. Ideal for very high temperatures or when frequent cleaning is needed.
Technical Specifications
Below is an example specification table for a typical United Shell & Tube Heat Exchanger model. Actual configurations are customized to your process requirements.| Specification | Example Value |
|---|---|
| Shell Outer Diameter | 500 mm (20 in) |
| Shell Length | 3000 mm (118 in) |
| Tube Outer Diameter | 19.05 mm (0.75 in) |
| Tube Wall Thickness | 1.65 mm (0.065 in) |
| Tube Length | 2800 mm (110 in) |
| Number of Tubes | 200 |
| Tube Layout | 30° Triangular Pitch |
| Flow Passes (Shell/Tubes) | 1 shell, 2 tube passes |
| Flow Arrangement | Counter-current |
| Heat Transfer Area | ~45 m² |
| Design Pressure (Shell) | 20 bar (290 psi) |
| Design Pressure (Tubes) | 25 bar (362 psi) |
| Design Temperature | 350 °C (662 °F) |
| Materials | Shell: CS (SA-516 Gr.70); Tubes: SS316 |
| Connections (Shell/Tubes) | 150 NB (6″) / 100 NB (4″) |
Specifications above are illustrative. United Heat Exchangers provides detailed calculations to match the exact heat duty and flow requirements of your system.
Applications in Industry
Shell-and-tube exchangers excel wherever large-scale heat transfer is needed. They are widely used in:- Oil & Gas: Refining crude oil requires preheating and condensation steps. United’s exchangers preheat crude by recovering heat from hot process streams and condense process gases by cooling them with seawater or cooling water. The rugged, high-pressure design handles extreme refinery conditions (high temperature and pressure) reliably.
- Chemical & Petrochemical: In chemical plants, these units regulate reactor temperatures and recover reaction heat. For example, they heat reactants entering reactors and then recover heat from reactor effluent to preheat incoming feed, improving overall efficiency. Their corrosion-resistant options are essential for handling acids, solvents, and other harsh chemicals.
- Power Generation: Shell-and-tube exchangers are the backbone of power plants. They serve as feedwater heaters (heating boiler water using exhaust steam) and steam condensers (condensing turbine exhaust steam back into water). United’s heavy-duty condensers and heaters enable plants to maximize energy recovery and maintain continuous operation under high flow rates.
- HVAC and Building Services: Large buildings and district cooling systems use shell-and-tube units for chilling and heating water. In chilled water systems, the exchanger cools circulating water by transferring heat to a refrigerant or ambient cooling fluid. For heating, it can transfer boiler heat to water loops. Its efficiency and ability to handle large volume flows make it ideal for commercial HVAC applications.
- Other Industrial Uses: These exchangers also appear in refrigeration, mining, pulp & paper, and water treatment. Anywhere robust heat exchange is needed—such as cooling lubricants, heating process fluids, or recovering waste heat—a shell-and-tube design can be applied.
Maintenance Tips and Best Practices
To keep United’s shell-and-tube exchanger running at peak efficiency, follow these maintenance practices:- Implement Regular Cleaning: Schedule routine cleaning to remove fouling and deposits. Deposits on tube walls impede heat transfer and increase pressure drop. Methods include mechanical cleaning (tube brushing, hydroblasting) or chemical cleaning with scale-dissolving solutions. A consistent cleaning regimen ensures the exchanger operates at optimal capacity.
- Inspect Frequently: Perform periodic inspections of both shell and tube sides. Look for signs of corrosion, erosion, or pitting in tubes and shells. Early detection of wear (e.g., thinning tube walls or leaks) allows corrective action before a failure. For example, visual checks or nondestructive testing of welds and tubes can catch issues early.
- Monitor Performance: Track inlet/outlet temperatures and pressure drop over time. A rising pressure drop or declining temperature difference usually signals fouling. Use this data to predict cleaning intervals. Keeping good records of performance also helps in troubleshooting and in optimizing maintenance schedules.
- Check Connections and Seals: Ensure flange bolts are properly torqued to prevent leaks. Replace any worn gaskets or O-rings during shutdowns. Although most United units have welded internals, check external joints for integrity.
- Use Proper Tube Plugs: In the event of a minor leak, use approved tube plugs to isolate affected tubes without shutting down the entire system. United supports quick repair kits to minimize downtime.
- Avoid Thermal Shocks: When starting or stopping, bring fluids up to temperature gradually. Sudden temperature changes can strain the metal. Heating or cooling the unit slowly prevents fatigue.
- Fluid Allocation: Follow good engineering practice for fluid placement. For example, put the fluid more likely to foul or corrode on the tube side (so tubes can be cleaned). This minimizes risk to the shell and simplifies maintenance.
Comparison to Alternative Heat Exchangers
While shell-and-tube exchangers are highly versatile, it’s useful to compare them to other types:- Plate Heat Exchangers: These use corrugated metal plates to transfer heat. Plate units offer much larger surface area in a given footprint, and they can achieve closer temperature approaches. In fact, plate heat exchangers can be up to five times more efficient per unit volume than shell-and-tube designs. However, they rely on thin gaskets between plates. These gaskets wear out with high temperatures or many cycles, leading to frequent replacements. By contrast, shell-and-tube units are typically welded internally and have no fragile gaskets to replace. Shell-and-tube exchangers also handle higher pressures and dirty or viscous fluids better than gasketed plates. In short, plates win for compactness and efficiency in clean fluid duties, whereas shell-and-tubes win for robustness and heavy-duty service.
- Double-Pipe (Tube-in-Tube) Exchangers: These consist of one tube nested inside another (usually two concentric pipes). They are simple and cheap, suitable for very small flow rates and low heat duties. However, they provide a very limited heat transfer area compared to shell-and-tube designs. For larger flows or temperature changes, multiple double-pipe units would be needed, making the system bulky. Shell-and-tube exchangers can handle the same service with a single compact unit, making them more efficient for most industrial applications.
- Air-Cooled and Finned-Tube Exchangers: Used when water is scarce or for gas cooling, these pass fluid through tubes with fins and air over them. While important in specific scenarios (like engine cooling), they generally belong to a different category (air as cooling fluid). For liquid-to-liquid duties, as in oil & gas or chemical plants, shell-and-tube remains the primary choice.
- Special Designs (Spiral, Scraped Surface, etc.): Other exotic designs exist for niche cases (e.g., highly viscous fluids or thermal storage). Those each have special advantages, but for general industrial heating/cooling duties, shell-and-tube offers the best all-around solution.
Why Choose United Heat Exchangers’ Shell and Tube Units?
United Heat Exchangers leverages decades of engineering expertise to deliver heat exchangers tailored to your needs. Our Shell & Tube Heat Exchangers are:- Engineered for Your Process: We calculate the exact size, tube count, and flow arrangement for your thermal duty. Every unit is custom-designed (within standard tooling) to hit the required temperatures and flow rates with minimum pressure drop.
- Quality-Assured: Fabrication follows ASME and TEMA standards, ensuring leak-tight construction and safe operation. All welds and materials are inspected per our quality control procedures.
- Reliable Performance: By choosing robust materials and proven designs, our exchangers run continuously in harsh environments. Customers in the oil & gas, power, and chemical industries trust United’s units to withstand 24/7 operation with minimal downtime.
- Service Support: We provide full documentation, recommended maintenance plans, and retrofit services. Should you need repairs or recertification, United’s service team is ready to assist with replacement bundles, gaskets, or upgrades.
- Cost-Effective: With a long operating life and low maintenance needs, a United shell-and-tube exchanger delivers excellent return on investment. Avoiding frequent shutdowns and part changes saves money over the equipment’s lifespan.