| Quick Summary
A shell and tube heat exchanger functions to transfer heat between the two types of fluid- one fluid that flows through the tubes of the shell and another fluid that flows in the outer shell and does not mix with any other fluid. There are basically three types of heat exchanger which are subject to trade offs on cost of materials, expansion and ease of cleaning. Baffles are used to direct the flow of the fluid through the shells which increase turbulence thereby increasing the heat transfer.Certainly, shell and tube heat exchangers are used extensively in oil & gas, energy and power generation, chemical industries, HVAC, marine and food industries, and are usually designed under TEMA and pressure vessel code including ASME. |
Shell and Tube heat exchanger is the most popular type of heat exchanger in use today in industry because it offers reliability when handling considerable pressures as well as dealing with considerable heat. What is more, Shell and Tube heat exchangers have lots of options starting from small and easy to assembly type to very big practical units having many hundreds or even thousands tubes. If your work is connected with such industries as oil and gas, energy production, chemical processing then there is a great probability of utilizing this type of heat exchanger in your production.
This guide covers what a shell and tube heat exchanger is, how it works, the main construction types, its key components, typical applications, and what to look for when selecting one or the heat exchanger tubes that go inside it.
What Is a Shell and Tube Heat Exchanger?
A shell and tube heat exchanger is a device that transfers heat between two fluids without allowing them to physically mix. It consists of a cylindrical outer shell (a pressure vessel) that houses a bundle of tubes. One fluid flows inside the tubes (the tube-side fluid), while the second fluid flows around the outside of the tubes, within the shell (the shell-side fluid). Heat passes from the hotter fluid to the cooler one through the tube walls, which act as the heat transfer surface separating the two streams.
Because the tube bundle can contain anywhere from a handful of tubes to several thousand, shell and tube exchangers offer a large amount of heat transfer surface area within a relatively compact footprint — one of the main reasons they remain the workhorse exchanger type across heavy industry.
How Does a Shell and Tube Heat Exchanger Work?
The working principle is straightforward:
- The hot fluid enters through a nozzle on either the shell side or the tube side (the choice depends on the fluid properties — more on that below).
- As it travels through the exchanger, it comes into thermal contact with the tube wall separating it from the second fluid.
- Heat transfers across the tube wall by conduction, and by convection on each fluid side.
- The cooled (or heated) fluid exits through an outlet nozzle at the opposite end.
Fluids can flow in the same direction (parallel flow), opposite directions (counter-flow, which is thermally the most efficient), or a combination of both when the exchanger has multiple tube or shell passes. Baffles inside the shell direct the shell-side fluid back and forth across the tube bundle in a zig-zag pattern rather than letting it flow straight through, this increases turbulence and velocity across the tubes, which significantly improves the heat transfer rate. Baffles also physically support the tube bundle and reduce vibration caused by fluid flow.
Key Components of a Shell and Tube Heat Exchanger
- Shell: The outer cylindrical pressure vessel that contains the tube bundle and the shell-side fluid. Smaller diameter shells are typically made from pipe; larger shells are rolled from steel plate.
- Tube Bundle: The group of parallel heat exchanger tubes through which the tube-side fluid flows. Tube material is selected based on the fluid’s corrosiveness, operating temperature, and pressure.
- Tubesheet: A thick, precision-drilled plate at one or both ends of the exchanger that holds the tube ends in place and separates the shell-side fluid from the tube-side fluid. Tubesheet design and material selection directly affect leak-tightness and service life. See our detailed guide on what a tubesheet is and how it’s designed for more.
- Baffles: Plates spaced along the shell length that direct shell-side flow across the tube bundle and support the tubes against sagging and vibration. Common types include segmental, disc-and-donut, and rod baffles.
- Channel/Head: The end covers that direct the tube-side fluid into and out of the tube bundle, and allow access for inspection and cleaning.
- Nozzles: Inlet and outlet connections on the shell and channel through which the two fluids enter and exit.
Types of Shell and Tube Heat Exchangers
Shell and tube exchangers are classified by how the tube bundle is constructed and how it accommodates the thermal expansion that occurs when the tube bundle and shell operate at different temperatures. The three main types are fixed tubesheet, U-tube, and floating head.
1. Fixed Tubesheet Heat Exchanger
In a fixed tubesheet design, both tubesheets are welded directly to the shell. This is the simplest and most economical construction, with the fewest gasketed joints and therefore the lowest risk of shell-side leakage. However, because the tubesheets are rigidly fixed, this design has limited ability to absorb differential thermal expansion between the shell and the tubes — an expansion joint may be needed in the shell if the temperature difference is large. The shell side also cannot be mechanically cleaned or inspected internally, which makes fixed tubesheet exchangers best suited to clean, non-fouling shell-side fluids.
2. U-Tube Heat Exchanger
In a U-tube design, the tubes are bent into a U-shape and both ends are fitted into a single tubesheet at one end of the shell, so the whole bundle can be pulled out for external cleaning or replacement. Because each tube is free to expand and contract independently, this design handles thermal expansion very well without needing an expansion joint, and it tends to be one of the most economical configurations. The trade-off is that the inside of the U-bends is difficult to clean mechanically, so U-tube exchangers are generally used where the tube-side fluid is relatively clean. For a closer look at bend design, fabrication tolerances, and common failure modes, see our post on U-bend tubes in heat exchangers.
3. Floating Head Heat Exchanger
In a floating head design, one tubesheet is fixed to the shell while the other “floats” freely inside a separate head, allowing the entire tube bundle to expand or contract independently of the shell. This makes it the most versatile configuration; it accommodates large temperature differentials and allows both the tube side and shell side to be mechanically cleaned, since the whole bundle can be removed. It’s also the most expensive design due to the additional internal gasket and more complex construction, and there’s a slightly higher risk of internal leakage at the floating head joint.
Comparing the Three Types
| Feature | Fixed Tubesheet | U-Tube | Floating Head |
| Relative cost | Low | Lowest | Highest |
| Handles thermal expansion | Limited (may need expansion joint) | Good (tubes expand independently) | Best (whole bundle floats) |
| Bundle removable for cleaning | No | Yes | Yes |
| Shell-side mechanical cleaning | Not possible | Possible (outside of bundle) | Possible |
| Tube-side mechanical cleaning | Yes | Difficult at the U-bend | Yes |
| Individual tube replacement | Yes | Only outer row tubes | Yes |
| Best suited for | Clean shell-side fluid, small ΔT | Clean tube-side fluid, large ΔT, cost-sensitive jobs | Dirty fluids on either side, large ΔT, frequent maintenance |
Tube Layout and Pitch
Within the bundle, tubes are arranged in a repeating pattern most commonly triangular pitch or square pitch. Triangular pitch packs more tubes into a given shell diameter and promotes higher shell-side turbulence, which improves heat transfer, but it does not allow mechanical cleaning lanes between tubes. Square pitch (and rotated square pitch) leaves straight lanes between tube rows, which allows the outside of the tubes to be cleaned mechanically, an important consideration when the shell-side fluid is prone to fouling. The center-to-center spacing between tubes is called the pitch, and the gap between adjacent tube surfaces is called the clearance.
Flow Arrangement: Passes and Flow Direction
Either fluid can make more than one pass through the exchanger to increase velocity and improve heat transfer:
- Tube-side passes are created using U-tubes or by partitioning the channel head, and are usually configured as 1, 2, 4, or 6 passes.
- Shell-side passes are created by adding a longitudinal baffle inside the shell, or by connecting multiple shells in series.
Counter-flow arrangements (where the two fluids move in opposite directions) achieve the highest possible temperature difference across the exchanger and are generally the most thermally efficient configuration. Exchangers with an even number of tube passes are a compromise between true counter-flow and parallel flow, since part of the tube length will always be running in parallel with the shell-side flow direction.
Advantages of Shell and Tube Heat Exchangers
- High pressure and temperature capability: the cylindrical shell and tube geometry is inherently well suited to pressure vessel design codes, making this the default choice for demanding refinery, power, and petrochemical duties.
- Large heat transfer area in a compact volume: bundling hundreds or thousands of tubes into one shell packs significant surface area into a manageable footprint.
- Material flexibility: tubes, shell, and internals can each be specified in the material best suited to the fluid in contact with them, from carbon steel through to titanium and nickel alloys.
- Scalable and field-proven design: from small package units to exchangers with tens of thousands of square feet of surface area, the same basic construction principles apply, backed by decades of TEMA design standards.
- Serviceable: U-tube and floating head designs allow the bundle to be pulled for inspection, cleaning, or tube replacement without scrapping the whole unit.
Disadvantages to Consider
- Larger footprint and weight compared to compact exchanger types like plate heat exchangers, for the same duty.
- Shell-side cleaning can be difficult or impossible in fixed tubesheet designs.
- Multiple tube passes reduce true counter-flow efficiency compared to a pure counter-current arrangement.
- Floating head designs carry a higher capital cost due to the additional gasketed joint and machining.
Applications of Shell and Tube Heat Exchangers
- Oil & Gas / Refineries: Crude preheat trains, condensers, reboilers, and cooling of process streams in distillation and cracking units.
- Power Generation: Steam surface condensers, feedwater heaters, and lube oil coolers in thermal and combined-cycle plants.
- Chemical & Petrochemical Processing: Reactor cooling, interstage cooling, and process fluid heating in corrosive or high-pressure service.
- HVAC Systems: Water-cooled chillers and condensers in large commercial and industrial buildings.
- Marine & Offshore: Seawater-cooled lube oil and jacket water coolers on ships and platforms, typically built in copper-nickel or titanium tubing for corrosion resistance.
- Food & Beverage / Pharmaceutical: Pasteurization, sterilization, and CIP (clean-in-place) systems, generally using hygienic-finish stainless steel tubes.
How to Choose a Shell and Tube Heat Exchanger
- Decide which fluid goes on the tube side vs. shell side. As a general rule: put corrosive, high-pressure, fouling, or toxic fluids on the tube side (easier and cheaper to build in exotic alloys, and easier to clean/inspect); put viscous fluids, condensing/boiling fluids, and fluids where pressure drop must be minimized on the shell side.
- Match the construction type to your maintenance and thermal expansion needs. Fixed tubesheet for clean, low-ΔT, cost-sensitive duties; U-tube for a good balance of cost and thermal flexibility; floating head where both sides need periodic mechanical cleaning or ΔT is large.
- Select tube material for the fluid and temperature. Carbon and low-alloy steel for general, non-corrosive service; stainless steel for corrosion resistance and hygiene; titanium or copper-nickel for seawater and marine duty; nickel alloys for severe chemical or high-temperature service.
- Confirm the design standard. Most industrial exchangers are designed and fabricated to TEMA (Tubular Exchanger Manufacturers Association) standards, in combination with the applicable pressure vessel code such as ASME.
- Specify tube dimensions correctly. Outer diameter, wall thickness (specified by BWG Birmingham Wire Gauge rather than pipe schedule), tube length, and layout pattern should all be matched to the required heat duty and allowable pressure drop.
Solitaire Overseas supplies heat exchanger tubes in seamless and welded construction, U-bend and straight lengths, across the full range of materials used in shell and tube exchanger manufacture including stainless steel, carbon steel, duplex, nickel alloys, titanium, and copper-nickel to ASTM, ASME, and TEMA specifications.
Shell and Tube vs. Other Heat Exchanger Types
- Shell and Tube vs. Plate Heat Exchanger: Plate exchangers achieve closer-to-true counter-flow and higher heat transfer coefficients in a smaller footprint, but shell and tube units handle higher pressures, higher temperatures, and dirtier fluids more reliably, and are generally easier to repair in the field.
- Shell and Tube vs. Double Pipe Heat Exchanger: A double pipe exchanger is essentially a simplified single-tube version of a shell and tube exchanger — cheap and easy to build, but with far less surface area for a given size, making it impractical for large heat duties.
Conclusion
Shell and tube heat exchangers remain the default choice for demanding industrial heat transfer duties because of their pressure and temperature capability, material flexibility, and decades of proven design practice under TEMA standards. Choosing the right configuration of a fixed tubesheet, U-tube, or floating head along with the correct tube material and dimensions, has a direct impact on thermal performance, maintenance requirements, and total lifecycle cost. Solitaire Overseas manufactures and exports heat exchanger tubes in the full range of materials and standards used in shell and tube exchanger construction. Get in touch to discuss your specification.
Frequently Asked Questions
1. What is a shell and tube heat exchanger used for?
It’s used to transfer heat between two fluids without mixing them, in applications like refinery process cooling, steam condensing, power plant feedwater heating, and marine engine cooling.
2. What are the three main types of shell and tube heat exchangers?
Fixed tubesheet, U-tube, and floating head each offering a different balance of cost, thermal expansion handling, and ease of cleaning.
3. What is the difference between a fixed tubesheet and a floating head exchanger?
In a fixed tubesheet exchanger, both tubesheets are welded to the shell, making it simple and economical but limited in accommodating thermal expansion. In a floating head exchanger, one tubesheet floats freely, allowing the tube bundle to expand independently and be removed for cleaning on both the shell and tube side.
4. What standard governs shell and tube heat exchanger design?
Most shell and tube exchangers are designed and fabricated in accordance with TEMA (Tubular Exchanger Manufacturers Association) standards, along with the relevant pressure vessel code such as ASME.
5. Which fluid should go in the tubes and which in the shell?
As a general rule, corrosive, high-pressure, fouling, or toxic fluids go on the tube side, while viscous, condensing, or boiling fluids or fluids where pressure drop must be minimized go on the shell side.
6. What materials are used for shell and tube heat exchanger tubes?
Common materials include carbon steel, stainless steel (304/316), duplex and super duplex steel, titanium, copper-nickel, and nickel alloys like Inconel and Hastelloy, selected based on the fluid, temperature, and corrosion environment.
