Stainless Steel Coil Tube — Low-Temperature Air Supply Cooling Coil (Wenzhou Jixing Metal Materials Co., Ltd)
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered heat exchanger component designed specifically for low-temperature air supply (LTAS) air conditioning systems. These coil tubes serve as the core heat transfer elements within cooling coils, facilitating efficient thermal exchange between chilled water (or refrigerant) and the supply air stream. The product is engineered to meet the rigorous demands of modern commercial HVAC (Heating, Ventilation, and Air Conditioning) systems where low-temperature air delivery (typically 7–15 °C supply air temperature) is required for high-capacity, low-volume air distribution.
Based on extensive research into cooling coil heat transfer performance optimization, these coil tubes are designed to maximize the overall heat transfer coefficient (U-value) while minimizing pressure drop across the coil, thereby improving the coefficient of performance (COP) of the entire air conditioning system. The coil tube geometry, fin spacing, and tube layout are optimized to enhance air-side and water-side heat transfer simultaneously, reducing the risk of coil frosting under low-temperature operating conditions.
2. Material & Properties
2.1 Tube Material
- Primary Alloy: Austenitic stainless steel — SUS304 (UNS S30408) or SUS316L (UNS S31603), selected based on application requirements.
- Equivalent Standards: ASTM A213 / ASME SA-213 (for seamless tubes); EN 10216-5 (for welded tubes); GB/T 12771 (Chinese national standard for stainless steel welded tubes).
- Key Mechanical Properties:
- Tensile strength (Rm): ≥ 520 MPa (SUS304); ≥ 485 MPa (SUS316L)
- Yield strength (Rp0.2): ≥ 205 MPa
- Elongation (A): ≥ 40%
- Hardness (HV): 150–250 HV10
- Thermal Conductivity: 16.3 W/(m·K) at 20 °C (SUS304); 14.6 W/(m·K) at 20 °C (SUS316L)
- Operating Temperature Range: −196 °C to +870 °C (SUS304); −273 °C to +870 °C (SUS316L)
2.2 Fin Material
- Options: Aluminum (1100-O, 3003-H14) or stainless steel (SUS304) fins, depending on corrosion environment and thermal performance requirements.
- Fin Types: Plain fins, low-fin (wavy), or high-performance offset louvered fins with optimized fin pitch and louver angle for enhanced turbulence and heat transfer augmentation.
2.3 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, water-side scaling, and condensate corrosion.
- SUS316L grade provides superior resistance to chloride-induced pitting and crevice corrosion (critical for coastal or chemically aggressive environments).
- Passivation treatment (nitric acid or citric acid pickling) performed post-manufacture to ensure a stable, protective chromium oxide layer.
3. Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | Φ6.35 mm (⅜"), Φ9.52 mm (⅜"), Φ12.7 mm (½") |
| Tube Wall Thickness | 0.5 mm / 0.65 mm / 0.8 mm / 1.0 mm |
| Tube Length | 1.0 m, 1.5 m, 2.0 m, 3.0 m (customizable up to 6.0 m) |
| Tube Pitch (Center-to-Center) | 12.7 mm / 15.875 mm / 19.05 mm (transverse & longitudinal) |
| Tube Layout | Inline (square), staggered (rotated square), or hexagonal |
| Number of Tube Rows | 2, 4, 6, 8 rows (configurable) |
| Fin Pitch | 1.8 mm / 2.0 mm / 2.2 mm / 2.5 mm (approx. 10–14 fins per inch) |
| Fin Height | 6.0 mm – 12.0 mm |
| Circuit Count | 2, 4, 6, 8, 12 circuits (per coil assembly) |
| Design Pressure (Water Side) | 1.0 MPa (standard); 1.6 MPa / 2.5 MPa (high-pressure options) |
| Design Temperature (Water Side) | 1 °C to 60 °C (chilled water); up to 95 °C (hot water) |
| Design Air Velocity | 2.0 – 4.5 m/s (face velocity) |
| Coil Face Area | 0.5 m² to 10.0 m² (custom sizes available) |
| Weight (Typical) | 1.5 – 25 kg per coil unit (depending on configuration) |
| Surface Finish | 2B (cold-rolled), BA (bright annealed), or No. 4 brushed finish |
| Connection Type | Flanged, threaded (BSP/NPT), brazed, or welded headers |
| Standard Reference | ASHRAE Standard 34; EN 12830; GB/T 19232 |
4. Manufacturing Process
- Raw Material Selection & Inspection: Certified stainless steel coils or seamless tubes are sourced from approved mills. Incoming material undergoes visual inspection, dimensional verification, and spectroscopic chemical analysis (OES) to confirm alloy composition compliance.
- Coil Winding / Tube Forming: Stainless steel strip or tube is precision-wound into the desired coil geometry using CNC-controlled coil winding machines. The winding process ensures consistent tube pitch, uniform row alignment, and controlled tube-to-tube spacing critical for balanced airflow distribution.
- Fin Application: Fins are applied via one of the following methods:
- Fin-on-tube (FOT) method: Pre-formed aluminum or stainless steel fins are mechanically expanded onto the tube surface using hydraulic or mechanical finning equipment.
- Continuous finning: The coil is passed through a continuous finning line where fins are simultaneously cut and expanded around the tubes.
- Header & Connection Fabrication: Stainless steel headers (water inlet/outlet manifolds) are fabricated and welded (TIG welding / GTAW) or brazed to the coil ends. Circuit distribution is designed to ensure uniform flow distribution across all tubes, minimizing maldistribution losses.
- Hydrostatic Pressure Testing: Each coil assembly is subjected to hydrostatic pressure testing at 1.5× the design pressure (minimum 1.5 MPa for standard coils) for a holding period of no less than 5 minutes to verify leak-tightness and structural integrity.
- Passivation & Surface Treatment: Post-weld passivation using citric acid or nitric acid solution to restore and stabilize the chromium oxide passive layer, enhancing long-term corrosion resistance.
- Performance Testing: Selected samples undergo air-side and water-side performance testing per ASHRAE Standard 34 procedures to verify heat transfer capacity, pressure drop, and overall thermal performance against design targets.
- Quality Control & Packaging: Final dimensional inspection, visual examination, and documentation review are completed. Coils are packaged in protective wooden crates or shrink-wrapped with corner protectors for shipping.
5. Applications
- Low-Temperature Air Supply (LTAS) Systems: Primary application — cooling coils for high-capacity, low-volume air distribution in commercial buildings, hospitals, data centers, and clean rooms.
- Chilled Water Air Handling Units (AHUs): Integrated cooling coils for rooftop units, packaged air handlers, and central air conditioning systems.
- Heat Recovery Systems: Air-to-air and air-to-water heat recovery coils in energy-efficient HVAC systems.
- Industrial Process Cooling: Temperature control in food processing, pharmaceutical manufacturing, and chemical plants where stainless steel corrosion resistance is mandatory.
- Marine & Coastal Applications: SUS316L coil tubes for HVAC systems in marine environments or coastal regions exposed to salt spray and chloride-laden atmospheres.
- Free Cooling / Economizer Systems: Outdoor air coils for free cooling applications in temperate climates.
- Refrigeration Evaporators: Air-cooled evaporator coils for commercial refrigeration systems.
6. Quality Certifications & Standards Compliance
- ISO 9001:2015 — Quality Management System certification for manufacturing processes.
- ISO 14001:2015 — Environmental Management System certification.
- CE Marking — Compliance with European Machinery Directive and Pressure Equipment Directive (PED 2014/68/EU) where applicable.
- ASME SA-213 / ASTM A213 — Material specification compliance for seamless stainless steel tubes.
- EN 12830 — European standard for air heat exchangers (air-to-water, air-to-air).
- ASHRAE Standard 34 — Methods for performance rating of air-to-water heat exchangers.
- GB/T 19232 — Chinese national standard for air conditioners and heat pumps (product performance testing).
- GB/T 12771 — Chinese national standard for welded stainless steel tubes.
- TÜV / SGS — Third-party inspection and testing reports available upon request.
7. Unique Selling Points
Research-Driven Thermal Optimization: The coil tube design is informed by advanced research into low-temperature air supply cooling coil heat transfer performance optimization. Computational Fluid Dynamics (CFD) modeling and experimental validation have been employed to optimize fin geometry, tube layout, and circuit distribution for maximum thermal efficiency.
- Enhanced Heat Transfer Performance: Optimized fin geometry (louvered or wavy fins) increases air-side turbulence, improving the overall heat transfer coefficient by 15–25% compared to conventional plain-fin coils.
- Superior Frost Resistance: Staggered tube layout and optimized air-side velocity distribution minimize uneven frost formation under low-temperature operating conditions, extending defrost cycle intervals and improving system reliability.
- Low Pressure Drop Design: Carefully engineered tube pitch and fin spacing minimize air-side and water-side pressure drops, reducing fan and pump energy consumption.
- Full Stainless Steel Construction: End-to-end stainless steel construction (tube + header) eliminates galvanic corrosion risks and ensures long service life (25+ years) even in aggressive chemical or marine environments.
- Customizable Configurations: Flexible design options accommodate a wide range of thermal loads, space constraints, and system requirements — from compact unitary coils to large central plant coils.
- Traceable Quality: Every coil is accompanied by a full traceability package including material mill certificates, pressure test records, and performance test data.
8. Technical Support & Customization
Wenzhou Jixing Metal Materials Co., Ltd provides comprehensive technical support including thermal performance calculations, CFD analysis for custom coil designs, system integration guidance, and after-sales engineering consultation. Custom coil configurations — including non-standard tube diameters, specialized fin geometries, and bespoke circuit layouts — are available to meet project-specific requirements. All products are manufactured under a rigorous quality assurance framework to ensure consistent performance and compliance with international standards.