What Are the Main Types of Shell-and-Tube Heat Exchangers?

With the continuous progress of society, shell-and-tube heat exchangers have gradually entered our daily lives and become increasingly familiar to many people. Owing to their simple structure and convenient operation, they are widely favored. But do you want to gain a deeper understanding of their functions? In this article, we will provide a comprehensive overview of the categories of shell-and-tube heat exchangers and related knowledge.

Introduction to Shell-and-Tube Heat Exchangers

Shell-and-tube heat exchangers, also known as tubular heat exchangers, are a type of surface heat exchanger in which the wall of the tube bundle enclosed within the shell serves as the heat transfer surface.

They feature a relatively simple structure, reliable operation, and can be fabricated from various structural materials (mainly metals). They are capable of operating under high temperature and high pressure conditions, making them one of the most widely used types of heat exchangers.

Construction

A shell-and-tube heat exchanger consists of key components such as:

• Tube box (channel head)

• Shell

• Tube bundle (core component, with heat transfer tubes acting as the thermal elements that determine exchanger performance)

• Baffles (or baffle rods), which significantly influence heat transfer performance

• Tube sheets, which support and seal the tubes against the shell

The tube box and shell largely determine the exchanger’s pressure-bearing capacity and operational reliability.

Working Principle

As a type of surface heat exchanger, the shell-and-tube exchanger comprises:

• Tube side (tube pass): the fluid flows inside the tubes

• Shell side (shell pass): the fluid flows outside the tubes within the shell

When fluids of different temperatures pass through the tube side and shell side respectively, heat is transferred through the tube walls. The hotter fluid transfers heat to the cooler fluid: the hot fluid is cooled, and the cold fluid is heated, thereby achieving the process of heat exchange.

Types of Shell-and-Tube Heat Exchangers

Because the tube side and shell side fluids are at different temperatures, the shell and tube bundle also experience temperature differences. If the temperature difference is large, significant thermal stresses may develop, leading to tube bending, cracking, or detachment from the tube sheet.

When the temperature difference between the shell and tube bundle exceeds 50°C, compensation measures must be implemented to mitigate thermal stresses. Based on these measures, shell-and-tube heat exchangers can be divided into the following main types:

1) Fixed Tube-Sheet Heat Exchanger

• Structure: The tube bundle is fixed to the tube sheets, and the tube sheets are welded to the shell.

• Advantages: Simple and compact structure, able to withstand high pressure, low cost, tube side easy to clean, damaged tubes can be plugged or replaced. More tubes can be accommodated compared to U-tube exchangers.

• Disadvantages: Significant thermal stresses arise when there is a large temperature difference or different coefficients of thermal expansion between the shell and tubes, requiring flexible elements (e.g., expansion joints). The tube bundle cannot be withdrawn, limiting mechanical cleaning. The tube bundle cannot be replaced, leading to higher maintenance costs.

• Applications: Suitable when the shell-side medium is clean and not prone to fouling, and when the temperature difference is not large, or when the temperature difference is large but shell-side pressure is not high.

2) Floating Head Heat Exchanger

• Structure: Only one end of the tube sheet is fixed to the shell, while the other end is free to move relative to the shell (the floating head). The floating head consists of a floating tube sheet, hook ring, and floating head cover, and is detachable, allowing the tube bundle to be withdrawn from the shell. Thermal expansion of the shell and tube bundle does not generate thermal stresses.

• Advantages: Removable tube bundle; when tubes are arranged in square or rotated square patterns, the tube bundle can be mechanically cleaned. Suitable for fouling or clogging fluids. One end is free to float, eliminating thermal stress issues, making it suitable for large temperature differences.

• Disadvantages: Complex structure, higher manufacturing cost, heavy equipment, higher material consumption. Floating head design reduces the number of tubes. Floating head sealing surfaces are prone to internal leakage during operation.

• Applications: Used when large temperature differences exist between shell and tubes, or when shell-side fluids are prone to fouling. Widely used in petroleum refining and ethylene industries. Typically limited to operating conditions of Pmax ≤ 6.4 MPa and Tmax ≤ 400°C.

3) U-Tube Heat Exchanger

• Structure: Only one tube sheet is used. The tube bundle consists of multiple U-shaped tubes, with both ends fixed to the same tube sheet. Tubes can expand and contract freely.

• Advantages: Free floating of U-bends effectively resolves thermal stress issues. Simple structure, low cost, strong pressure resistance.

• Disadvantages: Limited by tube bending radius, resulting in fewer tubes. Shell-side fluid flow may short-circuit. Failure of one U-tube equates to losing two passes, increasing scrap rates.

• Applications: Suitable for high temperature, high pressure, and large temperature difference conditions. Appropriate when the temperature difference between shell and tubes is large, or when shell-side fluids are fouling and require cleaning, but floating head or fixed tube-sheet designs are unsuitable.

4) Stuffing-Box (Packed) Heat Exchanger

• Structure: Similar to the floating head design, but the floating end extends outside the shell, sealed with a stuffing-box (packing gland).

• Advantages: Packing seals allow free axial movement of the tube bundle, preventing thermal stress. Easier to manufacture, saves material, lower cost. Tube bundle is removable, making maintenance convenient.

• Disadvantages: Packing seals are prone to leakage.

• Applications: Generally used under conditions ≤ 2.5 MPa. Not suitable for volatile, flammable, explosive, toxic, or expensive fluids. Service temperature is limited by the packing material properties. Now less commonly used.

Conclusion

The above overview of “the main types of shell-and-tube heat exchangers” and their basic introduction provides insight into this widely used type of heat exchanger. Understanding their structures, advantages, disadvantages, and suitable applications helps engineers and operators select the right design for specific process conditions.

If you need to learn about the specific specifications of heat exchangers (such as heat transfer area, design pressure/temperature, compatible media, and material selection), please feel free to contact us at any time. We will provide you with a complete parameter list and align with the details of your requirements simultaneously.

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