Stainless Steel Coil Tube (Coiltube) – Evaporative Cooler Grade
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered, continuously wound tubular product manufactured to meet the rigorous demands of heat transfer and mass transfer systems, particularly in evaporative cooling applications. Designed by Wenzhou Jixing Metal Materials Co., Ltd., this product is supplied in coiled form to facilitate seamless integration into coil-based exchangers, evaporative coolers, and thermal management systems. The coil configuration provides superior surface-area-to-volume ratios, enabling efficient convective and evaporative heat exchange under continuous industrial operating conditions.
Unlike straight tubular sections, coil tubes are formed through a controlled bending process that preserves the metallurgical integrity of the stainless steel while achieving precise geometric tolerances. The product is specifically engineered to withstand cyclic thermal loading, corrosive environments, and high fluid velocities encountered in evaporative cooling and condensation systems.
2. Material & Properties
2.1 Base Material Composition
The coil tube is fabricated from austenitic stainless steel grades conforming to international standards. The primary grade utilized is SAE 304 (UNS S30400) and SAE 316L (UNS S31603), selected for their excellent corrosion resistance, weldability, and thermal conductivity characteristics.
| Property | 304 (UNS S30400) | 316L (UNS S31603) |
|---|---|---|
| Carbon (C) Max | 0.08% | 0.03% |
| Chromium (Cr) | 18.0–20.0% | 16.0–18.0% |
| Nickel (Ni) | 8.0–10.5% | 10.0–14.0% |
| Molybdenum (Mo) | — | 2.0–3.0% |
| Tensile Strength (Rm) | ≥ 515 MPa | ≥ 485 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa |
| Elongation (A50) | ≥ 40% | ≥ 40% |
| Thermal Conductivity (20°C) | 16.3 W/(m·K) | 14.6 W/(m·K) |
| Density | 8.00 g/cm³ | 8.03 g/cm³ |
| Maximum Service Temperature | 870°C | 870°C |
2.2 Surface Treatment Options
- Pickled & Passivated (2B Finish): Standard surface treatment providing a smooth, corrosion-resistant finish suitable for most evaporative cooling applications.
- Mirror Polished (Ra ≤ 0.4 μm): Available for applications requiring minimal fluid friction and easy maintenance access.
- Electro-Polished: Enhanced surface integrity for high-purity fluid handling systems.
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Product Code | 1004 |
| Product Name | Coil Tube (Coiltube) |
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (1/4" – 2") |
| Wall Thickness | 0.5 mm – 3.0 mm |
| Coil Diameter | 100 mm – 1200 mm |
| Coil Length | Up to 200 m (continuous) |
| Bend Radius (Min.) | ≥ 3D (D = outer diameter) |
| Dimensional Tolerance (OD) | ± 0.05 mm |
| Dimensional Tolerance (Wall) | ± 10% |
| Flatness Deviation | ≤ 1.5 mm/m |
| Pressure Rating (Test) | 2.5 × Working Pressure (hydrostatic) |
| Working Pressure | Up to 4.0 MPa (PN40) |
| Temperature Range | −196°C to +600°C |
| Standards Compliance | ASTM A213 / A269, EN 10216-5, GB/T 12771 |
| End Condition | Plain, Beveled, or Threaded (BSP/NPT) |
| Packaging | Wooden reel with moisture barrier, or custom export packaging |
4. Manufacturing Process
The production of high-quality stainless steel coil tubes involves a multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical homogeneity, and surface integrity:
- Hot Rolling (Hot-Forging): Stainless steel ingots are hot-rolled into seamless tube blanks at temperatures exceeding 1100°C, ensuring uniform grain structure and eliminating internal voids.
- Pilger Drawing / Cold Drawing: The hot-rolled blanks undergo cold drawing through precision dies to achieve exact outer diameter and wall thickness tolerances. This process refines the grain structure and improves mechanical properties.
- Heat Treatment (Solution Annealing): Tubes are solution-annealed at 1050–1100°C followed by rapid quenching to dissolve carbides and restore full austenitic phase, maximizing corrosion resistance.
- Precision Coil Bending: The straight tubes are fed through a CNC-controlled bending machine that forms the coil geometry. The bending process employs internal mandrel support to prevent ovality and wrinkling, maintaining a minimum bend radius of 3D.
- Pickling & Passivation: The coiled tubes are immersed in a controlled acid bath (nitric/hydrofluoric acid mixture) to remove oxide scales, followed by passivation to form a protective chromium oxide layer.
- Quality Inspection: Each coil undergoes 100% visual inspection, dimensional verification, hydrostatic pressure testing, and (where applicable) eddy current flaw detection in accordance with ASTM A213/A269 requirements.
5. Applications
5.1 Evaporative Cooling Systems
Coil tubes serve as the primary heat exchange elements in evaporative coolers, where water films flow over the coil surfaces while air passes through, enabling highly efficient evaporative heat dissipation. Mathematical modeling of heat transfer and mass transfer in coiled tube evaporative coolers demonstrates that the helical geometry significantly enhances turbulent flow characteristics, increasing the Nusselt number (Nu) by 20–40% compared to equivalent straight tube configurations.
5.2 Industrial Applications
- Air Conditioning & HVAC Systems: Evaporator and condenser coils for commercial and industrial refrigeration units.
- Food & Beverage Processing: Pasteurization coils, condensers, and heat exchangers in dairy, brewery, and pharmaceutical production lines.
- Chemical Processing: Reactor cooling coils, distillation column condensers, and evaporator tubes in corrosive chemical environments.
- Petrochemical & Oil/Gas: Heat recovery systems, gas-cooled condensers, and process cooling loops.
- Power Generation: Feedwater preheaters, economizers, and auxiliary cooling systems in thermal and nuclear power plants.
- Marine Engineering: Seawater-cooled heat exchangers and condensers, leveraging 316L grade for chloride resistance.
- Solar Thermal Systems: Collector coils for concentrated solar thermal energy conversion.
6. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent production quality and process control. |
| ISO 14001:2015 | Environmental Management System demonstrating commitment to sustainable manufacturing practices. |
| ASTM A213 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High-Temperature Service. |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tube for Chemical and Similar Severely Corrosive Uses. |
| EN 10216-5 | European standard for non-alloy, low-alloy and high-alloy steels — tubes for heat exchangers and similar purposes. |
| GB/T 12771 | Chinese national standard for seamless stainless steel tubes for general purposes. |
| CE Marking | Conformity with European health, safety, and environmental protection standards. |
| Mill Test Reports (MTR) | Full traceability documentation including chemical composition, mechanical properties, and NDE results for every heat lot. |
7. Unique Selling Points
- Enhanced Heat Transfer Performance: The helical coil geometry promotes secondary flow patterns (Dean vortices) that intensify turbulent mixing, resulting in superior convective heat transfer coefficients compared to straight tube equivalents — a critical advantage for evaporative cooler design.
- Space-Efficient Installation: Coiled form factor reduces footprint by up to 60% compared to straight tube bank configurations, ideal for compact industrial installations.
- Continuous Coil Supply: Available in coils up to 200 meters, minimizing weld joints and potential leak points in the heat exchanger assembly.
- Full Metallurgical Integrity: Precision bending with internal mandrel support ensures zero ovality distortion, preserving uniform wall thickness and flow characteristics throughout the coil.
- Wide Grade Selection: Multiple stainless steel grades available (304, 304L, 316, 316L, 321, 347) to address specific corrosion and temperature requirements.
- Custom Fabrication Capability: OEM/ODM services including custom coil diameters, pitch spacing, end treatments, and coil-forming configurations tailored to specific evaporative cooler designs.
8. Mathematical Modeling Context
Research on "Mathematical Modeling of Heat Transfer and Mass Transfer in Coiled Tube Evaporative Coolers" has established that the performance of coil tube-based evaporative systems can be accurately predicted using coupled differential equations governing energy balance, species transport, and momentum conservation. Key parameters include the coil pitch, diameter ratio (D/d), flow velocity, and spray density. These models confirm that stainless steel coil tubes with optimized geometric parameters achieve thermal efficiencies exceeding 85% under standard operating conditions, validating the product's design specifications for high-performance evaporative cooling applications.