Introduction
When selecting tube options for industrial heat exchangers, engineers must choose configurations that will support the desired level of heat transfer. Fin tubes increase the external surface area of a conventional tube and are used in applications that benefit from additional heat exchange on that side.
There are several other parameters that contribute to the performance of a finned tube heat exchanger. Therefore, before ordering custom fin tubes, it is necessary to consider several aspects of their design, application, material, and manufacturing.
Overview
Fin tubes are widely applied in various industries. They are specifically used in heat exchangers, boilers, air coolers, and other heat transfer devices. Their main advantage is the ability to intensify heat transfer on the side with fins, which is typically the case for heat exchangers.
Depending on the application, a specific choice of fin tube material and design should be made. For example, the same fin tube should not be used in a boiler and a heat exchanger that operates under significantly different temperatures and pressures.
Custom fin tubes can be manufactured in a wide range of sizes and materials to meet all the required specifications and local conditions. The necessary design parameters should be indicated in the purchase specification to facilitate the ordering process.
Fin Tube Dimensions
It is vital to calculate the necessary fin tube dimensions to ensure that the tubes will accommodate the required equipment and operate under designed conditions. It is impossible to omit any dimensional specifications since tubes should not only fit the available space but also allow the intended flow rate.
The following parameters should be included in the purchase specification.
Tube Outside Diameter and Wall Thickness
The tube’s outside diameter (OD) should fit the designated space in the selected equipment. The wall thickness, along with the material, should meet the design pressure, temperature, and mechanical loading.
The wall thickness also affects the tube’s ability to conduct heat. However, this parameter does not always correlate with the overall performance, and its selection should be based on calculations and the entire heat exchanger’s design.
Tube Length and Finned Length
The length of the tube and its finned part should also be specified. It is vital to ensure that the length of the tube without fins (if any) will accommodate all the components that fix or move relative to the tube, such as the tube sheet and associated components.
The total length of the tube and the length of its finned section should also be indicated in the purchase specification. The difference between the total and finned lengths should be clearly specified.
Dimensional Tolerances
A purchase specification should also include the allowable deviations from the declared dimensions. The tube’s diameter, wall thickness, length, and other parameters have specific tolerances.
This information should be taken from the applicable standard, the technical drawing of the equipment, and the customer’s requirements. The selected tolerances should also be appropriate for the chosen method of joining the tube to the rest of the heat exchanger.
Fin Height and Fin Density
The two most common parameters that describe a finned tube are fin height and fin density. Both should be considered during the selection of tubes for a heat exchanger.
The height of the fins directly impacts the amount of heat that can be transferred through the finned tube. A tall fin increases the surface area, but it also makes the tube thicker. For this reason, it is vital to consider the available space and ensure that the selected fin height will not affect the flow of the fluid or gas through the tube.
Apart from the height, the density of the fins, also referred to as the number of fins per unit length, should also be specified. Increasing the density of the fins also increases the surface area of the tube.
However, it is vital to take into account the properties of the fluid or gas that will flow around the tube. If the working medium tends to stick to the surface of the tubes and form a layer of deposits, the distance between the fins should be sufficient to avoid additional pressure drop due to the formation of a deposit layer.
The combination of fin height and fin density that can be selected for a specific case depends on the heat exchanger’s design and the properties of the fluids or gases that will flow around the tube and inside it.
Fin Tube Material Specifications
The material from which tubes are manufactured should also be specified. It is vital to ensure that the selected material will be compatible with the flow of fluids or gases around the tubes and inside them.
For example:
- Carbon steel: A strong, durable, and relatively inexpensive material. However, its use in a boiler may be limited by the high operating temperatures and specific service conditions.
- Alloy steel: Can withstand higher temperatures and is more resistant to mechanical stress, depending on the selected grade.
- Stainless steel: Offers better corrosion resistance and can be used in aggressive environments, depending on the grade and operating conditions.
The choice of material also depends on the manufacturing method that will be used to produce the tubes.
The material of the tubes and the fins should also be compatible. Different materials can expand differently under the influence of heat, have different mechanical properties, and adhere to different standards.
Before placing an order, it is necessary to clarify whether there are any specific requirements regarding the composition of the tubes. The tube material should also meet all the specified standards, have the required mechanical properties, and be accompanied by all the necessary documents.
Manufacturing and Quality Checks
The manufacturing method and quality checks should also be discussed with the suppliers. A finned tube can be manufactured using various methods, and each of them has its advantages and disadvantages.
One of the factors that should be considered is the possibility of inspecting the tubes after manufacturing. The following parameters should also be discussed:
- Dimensional inspection: Diameter, thickness, and length of the tube and its fins.
- Material verification: Check whether the supplied material matches the declared material and ensure that all the necessary documents are provided.
- Fin attachment and condition: Visual and instrumental examination of the tubes to identify any flaws in the manufacturing process.
- Surface condition: The surface of the tubes should not have defects that can reduce their service life or the efficiency of the heat exchanger.
- Tests and documents: Type of tests, inspections, and documents that will be provided with the tubes.
Depending on the application, tubes should meet different standards and pass different tests. After defining all the requirements, they should be indicated in the purchase specification.
Not all the points described above should necessarily be included in the purchase specification. The required tests depend on the equipment, the conditions under which it will operate, and the customer’s preferences.
Purchase Specification
In general, a purchase specification should include all the parameters that define tubes and should be considered during their selection. A complete set of documents in accordance with the customer’s requirements will help the manufacturer select tubes that perform within the required parameters.
The following parameters should be indicated in the purchase specification:
- Tube material and grade.
- Tube outside diameter (OD).
- Tube wall thickness (WT).
- Tube length (TL) and finned length (FL).
- Fin height, fin density, and fin configuration.
- Fin tolerances, material, and type.
In addition, the purchase specification should indicate the applicable standards, the conditions under which the tubes will operate, the tests that they should pass, the required documents, the number of tubes, and all the other requirements and preferences of the customer.
Drawings should be provided if the tubes have any specific features that are not indicated in the purchase specification. All questions raised, or requirements that have not been clarified, should be discussed with the manufacturer before production starts.
Sainest Tubes manufactures fin tubes for industrial heat exchange applications. The company offers a variety of products and services that can be considered when selecting the tubes and submitting a purchase specification.
Conclusion
Ordering fin tubes for industrial projects requires careful consideration of dimensions, fin configuration, material compatibility, manufacturing methods, and quality checks. Clearly defining these requirements in the purchase specification helps ensure that the selected tubes meet the intended equipment and operating requirements.
By evaluating these factors before placing an order, engineers and buyers can make more informed decisions when selecting fin tubes for industrial heat exchange applications.