In a shell and tube heat exchanger, one fluid travels through the tubes while the other flows through the shell and around the outside of those tubes. At first glance, deciding which fluid goes where may seem straightforward. In practice, fluid placement can have a major effect on heat transfer performance, pressure drop, maintenance requirements, corrosion resistance, equipment cost, and long-term reliability.
There is no universal rule that says a certain type of fluid must always be placed on the shell side or tube side. Instead, engineers evaluate the operating conditions of both streams and determine the configuration that best fits the application.
Understanding these considerations can also help industrial buyers provide better information when getting a heat exchanger designed for a new or existing process.
What Is the Difference Between the Shell Side and Tube Side?
A shell and tube heat exchanger contains a bundle of tubes enclosed inside a larger pressure vessel called the shell.
Tube Side
The tube side refers to the fluid that flows through the inside of the individual tubes. Depending on the exchanger configuration, the fluid may make one or several passes through the tube bundle before leaving the unit.
Shell Side
The shell side refers to the second fluid, which flows through the space surrounding the outside of the tubes while remaining inside the shell.
Baffles and other internal components can be used to direct shell-side flow across the tube bundle, helping control velocity, heat transfer, vibration, and pressure drop.
How Do Engineers Decide Which Fluid Goes on Which Side?
Fluid allocation is normally based on several operating and mechanical considerations rather than a single rule.
Some of the most important factors include:
- Operating and design pressure
- Corrosion potential
- Fouling and scaling
- Fluid viscosity
- Required flow velocity
- Allowable pressure drop
- Phase change, such as condensation or boiling
- Cleaning requirements
- Materials of construction
- Maintenance access
Several of these factors may point toward different configurations, which is why fluid allocation should be evaluated as part of the complete thermal and mechanical design.
High-Pressure Fluids Are Often Placed on the Tube Side
When one process stream operates at substantially higher pressure than the other, engineers will often consider placing the higher-pressure fluid on the tube side.
The relatively small diameter of individual tubes can make containing high pressure more practical than designing the entire shell for the same pressure.
This can help reduce the amount of heavier or more expensive pressure-retaining material required for the exchanger.
Pressure Is Not the Only Consideration
Although higher-pressure fluids are commonly placed inside the tubes, this is not an automatic rule. Corrosion, fouling, temperature, maintenance requirements, and pressure-drop limits must still be evaluated before determining the final configuration.
Fouling Fluids May Be Better Suited for the Tube Side
Fouling occurs when scale, sediment, biological growth, process material, or other deposits accumulate on heat transfer surfaces.
As deposits build, heat transfer can decrease while pressure drop increases.
When a fluid is expected to foul heavily, placing it inside straight tubes may make maintenance easier because the internal tube surfaces can often be mechanically cleaned.
Cleaning Accessibility Matters
The heat exchanger configuration changes the equation.
Straight tubes are generally easier to access mechanically than U-tubes. Likewise, some shell-side surfaces can be difficult to clean without removing the tube bundle or using chemical cleaning methods.
For that reason, the expected cleaning procedure should be considered during design, rather than after the exchanger has already been installed.
Corrosive Fluids Are Frequently Considered for the Tube Side
Corrosion can significantly affect material selection and the service life of a heat exchanger.
If one fluid requires a corrosion-resistant alloy, placing that fluid on the tube side may reduce the amount of specialized material required. Instead of constructing a large portion of the shell from the more expensive alloy, the design may be able to concentrate corrosion-resistant materials in the tubes, tubesheet, and associated tube-side components.
However, material compatibility must be evaluated for the specific process fluid, concentration, temperature, pressure, and operating environment.
Viscosity Can Influence Shell-Side vs. Tube-Side Selection
Viscous fluids can create another design challenge.
A highly viscous fluid may experience relatively poor heat transfer when flowing through tubes at low velocity. Shell-side flow can sometimes create more mixing as the fluid moves around the tube bundle and through the baffle arrangement.
This can make the shell side attractive for certain viscous services.
But there is a tradeoff. If that same viscous fluid also has a strong tendency to foul or contains suspended solids, cleanability may become more important than the potential heat transfer benefit.
This is where application-specific engineering becomes important.
Pressure, viscosity, fouling, flow rate, thermal performance, and cleaning requirements have to be evaluated together rather than independently.
Allowable Pressure Drop Can Determine Fluid Placement
Every process has a limit on how much pressure can be lost as fluid moves through the heat exchanger.
A greater number of tube passes, smaller flow passages, higher velocities, baffle arrangements, nozzle sizes, and other design variables can all influence pressure drop.
If one process stream has a particularly restrictive allowable pressure drop, the manufacturer may evaluate whether shell-side flow provides greater flexibility for that application.
This is one reason allowable pressure drop should be included when requesting a heat exchanger quote. KAM Thermal’s shell and tube heat exchanger RFQ checklist outlines the process data and operating information that can help manufacturers properly evaluate an application.
What About Condensing or Boiling Fluids?
Phase-changing applications introduce additional considerations.
Vapors that are condensing are commonly evaluated for shell-side service because the shell provides substantial flow area and can accommodate the changing volume associated with condensation.
Boiling applications may also require specialized exchanger configurations designed around vapor generation, disengagement, circulation, and pressure drop.
These applications should not be treated as simple liquid-to-liquid heat transfer problems. The exchanger configuration, orientation, internal components, and fluid allocation all need to work together.
Shell Side vs. Tube Side: General Design Considerations
The following table provides a simplified overview of some common considerations. These are engineering guidelines rather than universal design rules.
| Fluid Characteristic | Side Often Considered | Why |
|---|---|---|
| Higher-pressure fluid | Tube side | Smaller-diameter tubes can make high-pressure containment more practical. |
| Corrosive fluid | Tube side | May reduce the amount of corrosion-resistant alloy required. |
| Fouling or scaling fluid | Tube side in many designs | Straight tubes can often be accessed more easily for mechanical cleaning. |
| Highly viscous fluid | Shell side may be considered | Shell-side flow patterns can sometimes improve mixing and heat transfer. |
| Fluid with very limited allowable pressure drop | Shell side may be considered | Baffle configuration and shell geometry can provide additional design flexibility. |
| Condensing vapor | Shell side is commonly considered | The shell can provide greater flow area for vapor and condensate. |
No single row in this table should determine the design by itself. The final arrangement depends on the complete operating conditions.
Heat Exchanger Configuration Also Changes the Decision
The physical construction of the exchanger plays an important role in determining where each fluid should flow.
Fixed Tubesheet Heat Exchangers
Fixed tubesheet designs can provide a relatively simple and economical construction, but shell-side mechanical cleaning may be limited because the tube bundle cannot normally be removed from the shell.
That can make shell-side fouling an especially important consideration.
Removable Tube Bundle Designs
A removable bundle can provide greater access to the outside of the tubes and interior of the shell for inspection, cleaning, or repair.
This can make the exchanger more suitable for applications where shell-side maintenance is expected.
U-Tube Heat Exchangers
U-tube configurations allow the tubes to expand and contract as temperatures change, making them useful in applications with significant thermal expansion.
However, the curved portions of the tubes can be more difficult to clean mechanically than straight tubes.
These differences are part of why shell-side and tube-side allocation must be considered alongside the overall exchanger configuration.
TEMA Design Considerations
Shell and tube heat exchanger design is also commonly influenced by standards published by the Tubular Exchanger Manufacturers Association. TEMA standards provide widely recognized guidance related to the mechanical design, fabrication, testing, installation, and maintenance of tubular heat exchangers.
You can learn more through the official TEMA standards information.
KAM Thermal also has a practical guide explaining TEMA standards and exchanger classes for industrial buyers and engineers specifying shell and tube equipment.
There Is No Universal Shell-Side vs. Tube-Side Rule
It is tempting to reduce fluid placement to a short list of rules such as “high pressure goes in the tubes” or “dirty fluid goes in the tubes.”
Those guidelines can be useful starting points, but industrial applications rarely depend on one variable.
For example, one fluid might simultaneously be:
- Highly corrosive
- Very viscous
- Prone to fouling
- Operating at the lower pressure
- Limited to a very small allowable pressure drop
Some of those characteristics may favor tube-side placement while others favor shell-side placement.
The final decision requires balancing thermal performance, mechanical design, maintenance requirements, materials, pressure drop, reliability, and cost.
Information to Provide Your Heat Exchanger Manufacturer
If you are specifying a new shell and tube heat exchanger, provide as much information as possible about both process streams.
Useful information includes:
- Fluid names and chemical composition
- Flow rates
- Inlet temperatures
- Required outlet temperatures
- Operating pressure
- Design pressure and temperature
- Allowable pressure drop
- Density
- Viscosity
- Corrosion concerns
- Solids or contaminants
- Known fouling or scaling conditions
- Cleaning requirements
- Preferred materials of construction
- Space and installation limitations
The manufacturer can use this information to evaluate not only the required heat transfer area, but also which stream should travel through the tubes and which should travel through the shell.
Custom Shell and Tube Heat Exchangers for Industrial Applications
Choosing the shell side and tube side is just one part of designing a reliable heat exchanger. Tube size, tube count, pass arrangement, baffle design, materials, pressure ratings, nozzle configuration, thermal expansion, cleaning access, and applicable construction standards all work together.
KAM Thermal Equipment is a custom shell and tube manufacturer with experience designing and manufacturing heat exchangers for industrial applications. Our team evaluates the actual process conditions behind each application rather than forcing complex operating requirements into a one-size-fits-all configuration.
As a fourth-generation fabricator of specialized industrial products, KAM Thermal provides thermal design, mechanical engineering, manufacturing, replacement equipment, and tube bundle solutions for demanding industrial environments.
Need Help Determining the Right Configuration?
If you are specifying, replacing, or upgrading a shell and tube heat exchanger, KAM Thermal can review your process conditions and help determine the appropriate configuration for your application.
Call KAM Thermal Equipment at (631) 348-4800 to discuss your heat exchanger requirements.