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Function of the Finned Tube

Date:2022-06-02

When the temperature of the finned tube wall rises, the touch pressure between the fins and the tube changes and the touch thermal resistance changes, the value of which depends on the type of finned tube and the initial touch pressure. As the temperature increases, the tension of the wound fins rapidly decreases and therefore the touch thermal resistance rapidly increases; bimetallic rolling can maintain stability over a wide temperature range.

The base tube of a finned tube is maintained by fins to resist atmospheric corrosion. The various types of finned tubes have different atmospheric corrosion resistance due to the different maintenance areas. The various finned tubes are best maintained with bimetallic rolling. As for all finned tubes with a surface hot-dip galvanised treatment, they are also the most resistant to atmospheric corrosion. In chemical plants or coastal areas where the atmosphere contains some corrosive gases, attention should be paid to the selection of finned tube materials and types, and aluminium fins are prone to corrosion.

The heat transfer function of the finned tube is related to the thermal resistance of the touch between the fins and the pipe, which depends on the touch pressure between the two. Obviously, the heat transfer function of the welded and sleeve fin type is better, followed by the bimetallic rolled fin type, and the inlaid and wound fin type is worse. After the second rolling, the touch area of the KLM finned tube is increased by about 50%, independent of the outer diameter tolerance of the pipe. After repeated hot and cold cycles, it can still maintain outstanding touch, thus the touching thermal resistance is small and the heat transfer function is high. Due to the increased airflow disturbance, the total heat transfer coefficient of slotted finned tubes can be improved by about 20%.

The working pressure of many finned tubes depends on the material and wall thickness of the base tube, but is also related to the type of finned tube. Rolled (aluminium and copper base tubes) have a very low pressure resistance and are not suitable for air coolers. The inlay base tube has a rolling groove and the working pressure decreases with increasing working temperature.

Compressed air, water vapour or high pressure water is generally used to clean the air side of the finned tube of dust and dirt. This approach requires the fins to have a certain degree of rigidity.

The cost of production is lower for fins and higher for bimetallic rolled fins and sleeve fins from the point of view of fin material consumption. The cost of production is lower for wound fins, higher for bimetallic rolled fins and highest for sleeve fins. All finned tubes that require hot-dip galvanizing on the incoming and outgoing surfaces are more expensive to produce, both in terms of material consumption and production process.

Finned tubes are widely used in power and chemical industries, and many spiral heat exchange surfaces or threaded tubes can be regarded as finned tubes. It plays an important role in extending the heat exchange area and promoting turbulence, and plays an important role in single phase convection heat exchange and phase change convection heat exchange. The structure of a finned tube heat exchanger is fundamentally the same as a normal shell and tube heat exchanger. Only the finned tube is used instead of the light tube as the heat transfer surface. The finned tube heat exchanger is also commonly used to heat or cool the gas outside the tube, inside the tube after steam or water, such as air coolers, boiler coal economizers, radiators, etc.