HOW TO MAINTAIN YOUR FIN TUBE IN A OPTIMAL OPERATION
What is fin tube?
A fin tube is a tube that has small fins around the outside surface. These fins act as a filter and a mechanism to transfer heat from the material inside the tube to the outside space or vice versa. Fin tubes are used in applications that require a transfer of heat from a hot fluid to a colder fluid through the tube’s wall. The rate at which such heat transfer occurs depends on three factors:
The temperature difference between the two fluids.
The heat transfer coefficient between each of the fluids and the tube wall.
The surface area to which the fluid is exposed.
In the case of a bare (unfinned) tubes, where the outside surface area is not significantly greater than the inside surface area, the fluid with the lowest heat transfer coefficient will dictate the overall heat transfer rate. When the heat transfer coefficient of the fluid inside the tube is several times larger than that of fluid outside the tube (for example steam inside and oil outside), the overall heat transfer rate can be greatly improved by increasing the outside surface of the tube. In mathematical terms, the product of the heat transfer coefficient for the outside fluid multiplied by the outside surface area is made to more closely match the product of the inside fluid heat transfer coefficient multiplied by the inside surface area.
So the whole concept of finned tubes is to increase the outside surface area of the tube. As an example, a finned tube configuration of 2” (nominal, 2.375” actual) pipe with a ¾” high welded helical solid fin of 12 gauge thickness with 6 fins per inch has an outside surface area of 8.23 sq. ft. per linear foot; whereas the same bare pipe has an outside surface area of only .62 sq. ft. per linear foot. That is a 13X increase in the outside surface area. See Design Information for extensive tables of surface areas and fin weights.
Why is fin tube important?
Finned tubes are the heart of any gas–gas or gas-liquid type of heat exchanger. Finned tube banks are compact units of robust and corrosion-resistant construction. The type of finned tube is chosen (ie, the fin type and combination of materials) depending on the specific requirements of each process equipment unit. Commonly, tubes currently have circular cross-section fins. Convective heating surfaces with circular, square, or helical fins represent tube bundles or tube banks with staggered or in-line arrangement of tubes in cross-flow.
Fin tube types
Fin tube manufacturers produce a wide range of fin tubes. They are used in heat exchangers (air, water and chemically cooled) for various industries such as petroleum, petrochemical, steel, power generation and many more.
Corrosion protection processes are performed during fin tube manufacturing and the material used is corrosion-resistant. Some fin tube types are:
“L” fin tubes:
- Max working temperature – 150 °C (302 °F)
- Atmospheric corrosion resistance – acceptable
- Mechanical resistance – poor
- Fin material – aluminum, copper
“LL” fin tubes
- Max working temperature – 180 °C (356 °F)
- Atmospheric corrosion resistance – acceptable
- Mechanical resistance – poor
- Fin material – aluminum, copper
“KL” fin tubes
- Max working temperature – 260 °C (500 °F)
- Atmospheric corrosion resistance – acceptable
- Mechanical resistance – acceptable
- Fin material – aluminum, copper
“G” fin tubes
- Max working temperature – 400 °C (752 °F)
- Atmospheric corrosion resistance – poor
- Mechanical resistance – acceptable
- Fin material – aluminum, copper, carbon steel
Extruded fin tubes
- Max working temperature – 285 °C (545 °F)
- Atmospheric corrosion resistance – excellent
- Mechanical resistance – excellent
- Fin material – aluminum
Why we use fin tube?
By increasing the outside surface area of the tube, the overall heat transfer rate is increased, thereby reducing the total number of tubes required for a given application. This reduces the overall equipment size and the cost of the project. In many cases, one finned tube replaces six or more bare tubes at less than 1/3 the cost and ¼ the volume.
How to maintain fin tube
Generally, when water is used for circulation at the beginning of the operation, there may be slight leakage. When the temperature rises to the sterilization temperature, the leakage will disappear by itself. If the leakage does not stop, the finned tube must be compressed a little more. If it is still ineffective, it is necessary to open and check the rubber gasket. It is also possible that the finned tubes are arranged in the order of numbers on the fins, which should be corrected.
Regularly check whether the finned tubes are complete, whether there are deposits, coking, rust layer, and other scaling adhesion, and clean them immediately. At the same time, it is also necessary to check whether the adhesion between each fin tube and the rubber washer is tight and whether the rubber washer itself is in good condition, so as to avoid leakage caused by rubber washer degumming and damage.
When the rubber gasket needs to be replaced or the degummed part needs to be repaired, the finned tube shall be removed and placed on the table, and the old gasket shall be removed, or the glue traces in the groove of the finned tube shall be wiped out with fine sandpaper at the degumming position, and then the oil traces in the groove shall be wiped out with carbon tetrachloride or trichloroethylene, and then the back of the new rubber gasket shall be wiped out with fine sandpaper, similarly with carbon tetrachloride or trichloroethylene, the alkene solvent wiped out the oil. Then, apply a thin layer of glue on the back of the groove and rubber washer. Let it dry a little, but it still sticks. That is to say, the rubber washer is embedded in the groove, flattened around, and coated with a layer of talcum powder. Then install the fin tube and clamp it gently. According to the glue instructions, it can be used after a period of time.
When replacing the rubber gasket of the finned tube, it is necessary to update all the segments so as to avoid uneven clearance between the fins and affect the heat transfer effect.
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