Types of heat exchanger tubes

Heat exchanger tubes are crucial components within heat exchangers, facilitating the transfer of heat between two media. These tubes boast high thermal conductivity and excellent isothermal performance, making them highly efficient in transferring heat with minimal loss. Often referred to as heat transfer superconductors, their thermal conductivity is significantly higher than that of copper. This article will detail the various types of heat exchanger tubes.

Forms of Heat Exchanger Tubes

Besides plain tubes, heat exchangers can utilize various enhanced heat transfer tubes, including:

- Finned Tubes: Ideal when there is a significant difference in heat transfer coefficients on either side of the tube. The fins should be placed on the side with the lower heat transfer coefficient.

- Threaded Tubes

- Spiral Grooved Tubes

Sizes of Heat Exchanger Tubes

Common sizes (outer diameter×wall thickness) of heat exchanger tubes include:

Seamless Steel Tubes:φ19mm×2mm,φ25mm×2.5mm,φ38mm×2.5mm

Stainless Steel Tubes:φ25mm×2mm,φ38mm×2.5mm

Standard tube lengths are 1.5m, 2.0m, 3.0m, 4.5m, 6.0m, and 9.0m. Using smaller diameter tubes can increase the heat transfer area per unit volume, resulting in a compact structure, reduced metal consumption, and improved heat transfer coefficients. For instance, reducing the diameter fromφ25mm toφ19mm can increase the heat transfer area by approximately 40% and save over 20% of metal. However, smaller diameter tubes can lead to higher fluid resistance, making them harder to clean and more prone to scaling and clogging. Larger diameter tubes are generally used for viscous or dirty fluids, while smaller diameter tubes are preferred for cleaner fluids.

Materials for Heat Exchanger Tubes

Common materials include:

- Metals: Carbon steel, low alloy steel, stainless steel, copper, copper-nickel alloy, aluminum alloy, titanium

- Non-Metals: Graphite, ceramics, polytetrafluoroethylene (PTFE)

The appropriate material should be selected based on factors such as working pressure, temperature, and the corrosiveness of the medium.

Center Distance of Heat Exchanger Tubes

The arrangement of heat exchanger tubes on the tube sheet can be in:

- Equilateral Triangles: Allows the maximum number of tubes per unit area, commonly used but not ideal for external cleaning.

- Squares: Facilitates easier cleaning outside the tubes.

- Square Corners

The center distance between heat exchanger tubes should ensure adequate strength and width of the tube bridge when connecting to the tube sheet. If cleaning between the tubes is necessary, a cleaning channel should be reserved. The center distance should not be less than 1.25 times the outer diameter of the heat exchanger tube. Commonly used center distances for heat exchanger tubes are shown in the following table.

Heat exchanger tubes come in various forms, sizes, materials, and arrangements, each tailored to specific applications and operating conditions. Proper selection and arrangement of these tubes are essential to maximize the efficiency and longevity of heat exchangers in diverse industrial applications.