What is a finned tube?

Coil tube , sometimes referred to as “extended‑surface tubes.” As the name suggests, a finned tube is manufactured by machining numerous fins onto the surface of the base tube—whether on the outer or inner surface—thereby expanding the original surface area and creating a distinctive heat‑transfer element. Why are finned tubes used? And what effects does finning have on the base tube’s surface? To answer these questions, we must begin with some fundamental principles of the heat‑transfer process.

Heat transfer between a solid surface and the fluid in contact with it is called convective heat transfer. A common example of convective heat exchange is the heat transfer between the outer surface of a radiator and the surrounding air. Everyday experience tells us that the larger the radiator’s surface area, the higher its surface temperature (i.e., the greater the temperature difference between the surface and the air), and the longer the heating duration; the more heat is exchanged, and the warmer the room becomes. This demonstrates that convective heat transfer is directly proportional to the heat-transfer surface area, the temperature difference, and the duration of the process. To compare the intensity of convective heat transfer under different conditions, we introduce a physical quantity known as the “heat-transfer coefficient.” The heat-transfer coefficient represents the rate of convective heat transfer per unit area, per unit temperature difference (between the wall and the fluid), and per unit time.

Wound aluminum Coil tube It is an aluminum strip that, under the tension of a winding machine, is uniformly wound onto steel, copper, or stainless‑steel tubes at specified fin height, fin pitch, and fin thickness. The fin height can be customized according to operating conditions and specific requirements. Typical dimensions range from 10 mm to 20 mm in fin height, with fin thicknesses between 0.2 mm and 0.6 mm, fin pitches of 2.5–10 mm, and base tube diameters from 16 mm to 89 mm.

The fins surrounding aluminum‑wrapped tube heat exchangers are typically L‑shaped, with no exposed portion of the base tube and the spacing sections wrapped in aluminum strips. This design reduces thermal resistance and effectively enhances heat transfer performance. Aluminum‑wrapped tubes are generally suited for applications involving relatively small temperature differentials. However, their strength and hardness are inferior to those of extruded finned tubes. Therefore, under appropriate operating conditions, aluminum‑wrapped tubes can be selected to reduce costs while maintaining satisfactory heat‑transfer performance. Coil tube 。

The magnitude of the heat transfer coefficient primarily depends on the following factors:

L. Types and physical properties of fluids: For example, water and air have vastly different heat transfer coefficients; L. Whether the fluid undergoes a phase change during heat transfer—i.e., whether boiling or condensation occurs. If a phase change takes place, the heat transfer coefficient increases significantly.

L is also related to the fluid velocity and the geometry of the solid surface, among other factors. The magnitude of the convective heat transfer coefficient is typically determined through experimental studies; a set of commonly used conditions is provided below.

Value range:

Condensation of water vapor H = 10,000–20,000 W/(㎡·℃)

Boiling water: h = 7000–10000

L water convection: H = 3000–5000

L Forced convection of air or smoke: h = 30–50

Natural convection of air or flue gases: h = 3–5

It can be seen that the heat transfer coefficients vary considerably under different conditions. Keep in mind the numerical ranges of the heat transfer coefficients mentioned above; this will be of great assistance in understanding and selecting finned tubes in the future.