Oval Finned Tubes with Round Ends
Structural of Oval Finned Tubes with Rounded Ends
Base Tube: Oval Cross Section
The core base tube of this heat transfer element adopts an oval metal tube, with standard cross-sectional dimensions of 36mm × 14mm (major axis × minor axis). The oval design comprehensively considers fluid dynamics performance and pressurebearing capacity: the major axis direction aligns with the fluid flow direction, effectively reducing flow resistance; the minor axis direction facilitates a reduced tube pitch, resulting in a more compact equipment structure.
Fin: Square Fins
Square fins are used in conjunction with the base tube. The fin features a centrally located elliptical hole matching the outer contour of the base tube to ensure a tight fit. The advantages of square fins are:
- Large Extended Surface Area: Under the same projected area, square fins provide more heat transfer surface area than circular fins.
- Ease of Arrangement: The square profile facilitates the formation of regular airflow passages within the tube bundle, helping to optimize flow distribution.
- Structural Regularity: The manufacturing and assembly processes are mature, and costs are controllable.
Tube End: Round Ends
Although the main body of the base tube is oval, both ends are processed through a specialized expansion process, being rounded to a standard circular tube end with an outer diameter of 27.3mm.
The core value of this design lies in:
- Compatibility with Standard Interfaces: The circular ends can be directly connected to conventional circular tube sheets and headers.
- Reliable Sealing: Mature expansion or welding processes can be employed to ensure the tightness of the connection.
- Standardized Machining: Eliminates the need for customshaped holes in tube sheets, reducing manufacturing difficulty and cost.
Oval Finned Tubes with Round Ends
Manufacturing Processes of oval finned tube with Rounded Ends
The realization of this special structure relies on a set of mature processing procedures, particularly the methods for connecting the base tube and fins, as well as the tube end rounding process.
Connection Methods
3 main processes for base tube & fins connection
Expansion + Galvanizing
Sleeving + Copper Brazing
Sleeving + Tin Brazing
Tube End Rounding
Localized expansion with specialized mandrel
Target: 27.3mm outer diameter
Best for Copper & Copper Alloys
Not for Galvanized Steel Tubes
Material Requirements
Key plasticity for rounding process
Copper: Good plasticity, no cracking
Steel: Poor plasticity, zinc layer spalling risk
Galvanized tubes: Keep original ends
Connection Methods for Base Tube and Fins
Based on application scenarios, temperature resistance requirements, and cost considerations, the main processes for connecting square fins to the oval base tube are as follows:
- Expansion + Galvanizing: Fins are first slipped onto the tube. The tube diameter is expanded mechanically or hydraulically, causing the tubes outer wall to fit tightly against the fins inner hole. Subsequently, the entire assembly is hotdip galvanized. The molten zinc fills the microscopic gaps at the connection, ensuring good contact thermal conductivity while providing excellent corrosion protection for the entire element.
- Sleeving + Copper Brazing: Fins are threaded onto the tube one by one to the predetermined position. Copperbased brazing filler metal is added at the interface between the fin and tube, and the assembly is heated in a hightemperature furnace. The filler metal melts, wets the base materials, and forms a strong metallurgical bond upon cooling. This connection method offers high strength and good thermal conductivity, suitable for hightemperature or vibrating conditions.
- Sleeving + Tin Brazing (Soldering): The process is similar to copper brazing, but uses a tinbased filler metal with a lower melting point. This process operates at a lower temperature, resulting in minimal thermal impact on the base tube and fins. It is commonly used in mediumtolow temperature applications such as refrigeration and air conditioning.
Tube End Rounding Process
The process of transforming the oval tube end into a circular shape is achieved through localized expansion. A specialized expanding tool (mandrel) is inserted into the oval tube end, applying radial force to plastically deform the metal material until it becomes a standard circular tube (27.3mm outer diameter).
It is important to note that this rounding process has specific material requirements:
- Applicable to Copper and Copper Alloys: Copper possesses good plasticity (is relatively soft) and is not prone to cracking during the expansion process, allowing for a smooth transition from oval to circular.
- HotDip Galvanized Tubes are Typically Not Rounded: For finned tubes processed via hotdip galvanizing, the base tube surface is covered with a thick zinc layer, and the base tube material is often steel. The plasticity of steel is relatively poor; forcibly rounding the ends can easily lead to spalling of the galvanized layer or cracking of the base tube. Therefore, the tube ends of hotdip galvanized oval finned tubes usually maintain their original state.
Our Oval Finned Tube Cases
Theoretical advantages need to be validated in practice. The following are typical production cases of oval finned tubes delivered by us in recent years, all adopting the structure of 36mm×14mm oval base tube + square fins + tube ends rounded to 27.3mm. They have met the diverse needs of customers under different material combinations and surface treatment processes.
| Case | Base Tube Material | Fin Material | Surface Treatment | End Treatment |
|---|---|---|---|---|
| 1 | C70600 (CuNi 90/10) | C12200 (Phosphorus Deoxidized Copper) | None | Rounded to 27.3mm |
| 2 | C70600 (CuNi 90/10) | C12200 (Phosphorus Deoxidized Copper) | Full Tin Plating/Dipping | Rounded to 27.3mm |
| 3 | C68700 (Aluminum Brass) | Copper (T2) | None | Rounded to 27.3mm |
C70600 Tube + C12200 Fins
C70600 Tube + C12200 Fins + Tin Coating
C68700 Tube + Copper Fins
Case 1: Cupronickel Tube + Copper Fins
Material Combination: The base tube uses C70600 (90/10 cupronickel), and the fins use C12200 phosphorus deoxidized copper. Cupronickel has excellent seawater corrosion resistance and antibiofouling properties, widely used in ships, offshore platforms, and coastal power plants.
Process Features: The expansion + galvanizing process or copper brazing process ensures a tight bond between the fins and the base tube. After the tube ends are expanded and rounded, they can be directly connected to cupronickel or titanium tube sheets, meeting the requirements for highcorrosionresistance heat exchanger designs.
Case 2: Cupronickel Tube + Copper Fins + Full Tin Coating
Material Combination: Uses C70600 base tube and C12200 fins, with the addition of a full hotdip tin coating surface treatment.
Process Features: The tin coating offers good corrosion resistance and food safety certification, suitable for applications with strict requirements for medium purity, such as drinking water heating, food processing, and pharmaceuticals. The tinning process also fills the microscopic gaps between fins and tube, further reducing contact thermal resistance.
Case 3: Aluminum Brass Tube + Copper Fins
Material Combination: The base tube uses C68700 (aluminum brass), and the fins use copper. Aluminum brass has excellent corrosion resistance in fresh and brackish water, and its cost is lower than that of cupronickel, making it a traditional choice for power plant condensers and petrochemical industry air coolers.
Process Features: The sleeving + copper brazing process ensures connection reliability under hightemperature conditions. The rounded 27.3mm tube ends can be directly inserted into tube sheets for expansion.