Stainless Steel Coil Tube for Cross-Flow Fan Coil Unit (FCU) Systems
Product Overview
The Stainless Steel Coil Tube (Product No. 314) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component designed specifically for integration into Fan Coil Units (FCU) utilizing Cross-Flow Fans (also known as Transverse Flow Fans or Diagonal Flow Fans). This product represents the culmination of advanced structural design and optimization methodologies applied to coil tube architecture, enabling superior thermal exchange efficiency within compact HVAC (Heating, Ventilation, and Air Conditioning) assemblies.
The coil tube serves as the primary heat transfer medium within the FCU heat exchanger section, where refrigerant or heated water circulates through the serpentine tube configuration to facilitate convective heat exchange with ambient air drawn across the coil face by the cross-flow fan mechanism. The design philosophy emphasizes minimized flow resistance, maximized surface-to-volume ratio, and structural integrity under cyclic thermal loading.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional corrosion resistance, thermal conductivity, and mechanical durability in HVAC operating environments.
- Primary Alloy Grade: SUS304 / ASTM A269 TP304 (18/8 Stainless Steel)
- Alternative Grade: SUS316 / ASTM A269 TP316 (with Mo addition for enhanced chloride resistance)
- Chromium Content: 18.0–20.0%
- Nickel Content: 8.0–10.5%
- Molybdenum Content (316 grade): 2.0–3.0%
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Corrosion Resistance: Excellent resistance to oxidation at temperatures up to 870°C; superior resistance to condensation water corrosion
- Mechanical Properties: Tensile strength ≥ 520 MPa; Yield strength ≥ 205 MPa; Elongation ≥ 40%
- Operating Temperature Range: −196°C to +870°C
- Surface Finish: 2B / BA (Bright Annealed) / No. 4 Brushed finish options
Specifications
| Parameter | Specification |
|---|---|
| Product No. | 314 |
| Product Name | Coil Tube (盘管) |
| Outer Diameter (OD) | 7.0 mm / 8.0 mm / 9.53 mm (3/8") / 12.7 mm (1/2") |
| Wall Thickness | 0.5 mm – 1.2 mm (customizable) |
| Tube Length (per circuit) | 300 mm – 1,200 mm (configurable) |
| Number of Rows | 1 – 6 rows (standard); up to 10 rows (special order) |
| Number of Passes | 1 – 4 passes (standard) |
| Fin Spacing (FPI) | 10 – 14 fins per inch (standard); 16 FPI (high-performance) |
| Fin Material | Aluminum (Al-Mg-Si alloy) or Stainless Steel |
| Tube Pitch (Lateral) | 19.05 mm (3/4") / 22.2 mm (7/8") |
| Row Pitch (Depth) | 28.6 mm – 38.1 mm |
| Maximum Working Pressure | 1.6 MPa (standard); 2.5 MPa (reinforced) |
| Hydrostatic Test Pressure | 2.4 MPa (standard); 3.8 MPa (reinforced) |
| End Connection Type | Flared / Threaded (M10×1) / Brazed / Soldered |
| Applicable Refrigerants | R410A / R32 / R134a / R22 / Water / Glycol-Water mixture |
| Coil Dimensions (W×H×D) | Customized: 400×250×70 mm to 1,000×400×200 mm |
| Cross-Flow Fan Compatibility | Integrates with 150 mm – 350 mm diameter cross-flow fans |
| Weight | 0.8 kg – 4.5 kg (depending on configuration) |
| Coating / Treatment | Hydrophilic aluminum coating (standard); Anti-corrosion passivation treatment |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing protocol optimized for dimensional accuracy, thermal performance, and long-term reliability:
- Material Preparation: Raw stainless steel seamless tubing is received, inspected for chemical composition compliance (Spectrometer Analysis), and verified against ASTM A269 / GB/T 12771 standards.
- Cutting & Deburring: Precision CNC cutting to specified circuit lengths with automated deburring to eliminate internal protrusions that could impede fluid flow.
- Forming & Bending: Computer-controlled CNC tube bending machine forms the serpentine coil geometry with precise bend radii (typically 3× OD to 5× OD) to minimize stress concentration and prevent wall thinning at bend apexes.
- Fin Attachment: Aluminum or stainless steel fins are mechanically attached via slitting-and-insertion (finning) process or welded onto the tube surface using resistance welding or brazing techniques to ensure thermal contact integrity.
- Hydrophilic Coating Application: For evaporator coils, a hydrophilic aluminum coating is applied via electrostatic spray or immersion method to enhance condensate drainage and reduce frosting.
- Passivation Treatment: Chemical passivation using nitric acid or citric acid solution forms a stable chromium oxide protective layer on the stainless steel surface.
- Pressure Testing: Each coil assembly undergoes 100% hydrostatic pressure testing at 1.5× the maximum working pressure, held for a minimum of 5 minutes to verify leak-tightness.
- Dimensional Inspection: Coordinate Measuring Machine (CMM) verification of critical dimensions including tube pitch, row depth, and overall coil envelope.
- Final Cleaning & Packaging: Ultrasonic cleaning to remove residual flux and contaminants, followed by protective packaging with moisture-absorbent desiccants.
Applications
The stainless steel coil tube (No. 314) is specifically engineered for integration with Cross-Flow Fan Coil Units, a configuration that offers distinct advantages over conventional axial or centrifugal fan arrangements:
- Commercial HVAC Systems: Office buildings, hotels, shopping malls, and hospitals requiring low-noise, high-efficiency temperature regulation with compact installation footprints.
- Cross-Flow Fan Integration: The coil tube design accommodates the unique airflow pattern of cross-flow fans, where air enters tangentially and exits axially, requiring optimized tube arrangement to minimize pressure drop while maximizing heat transfer area exposure.
- Residential Ductless Systems: Concealed ceiling-mounted and wall-mounted FCU units for premium residential applications.
- Industrial Process Cooling: Precision temperature control in electronics manufacturing, pharmaceutical cleanrooms, and laboratory environments.
- Marine & Coastal Applications: SUS316 grade coils provide superior resistance to salt-laden atmospheric corrosion in marine HVAC systems.
- Food Processing & Medical Facilities: Hygienic-grade stainless steel construction meets FDA and GMP (Good Manufacturing Practice) requirements for sanitary environments.
Structural Design Optimization Features
Based on the research and development methodology outlined in "Structure Design and Optimization of Fan Coil Units Based on Cross-Flow Fans", the following optimization principles are incorporated into the coil tube design:
Key Optimization Principles:
- Variable Tube Pitch: Non-uniform lateral tube spacing is employed to compensate for airflow velocity gradients across the coil face in cross-flow fan configurations, ensuring uniform heat transfer distribution.
- Staggered Fin Arrangement: Fin geometry is optimized to promote turbulent boundary layer development at the critical Reynolds number range (Re = 200–500) typical of cross-flow fan operating velocities (1.5–3.5 m/s face velocity).
- Reduced Pressure Drop: The serpentine circuit layout minimizes flow resistance by optimizing bend radii and circuit count, achieving a pressure drop reduction of 15–25% compared to conventional coil designs.
- Enhanced Condensate Management: Tube row arrangement is designed to facilitate gravity-driven condensate drainage, preventing water accumulation and associated efficiency degradation.
- Compact Form Factor: Multi-pass circuit configuration enables high heat transfer capacity within a reduced coil depth, compatible with the space-constrained housing of cross-flow FCU units.
Quality Certifications & Standards Compliance
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ASTM A269/A269M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for Chemical and Fossil Fuel Process Plants
- GB/T 12771 — Chinese National Standard for Stainless Steel Seamless Tubes
- EN 10217-7 — European Standard for Stainless Steel Tubes for Mechanical and General Engineering Purposes
- ASME B31.5 — Pressure Piping and Piping Components for Refrigeration and Air-Conditioning
- UL 1995 — Standard for Air-Conditioning and Heat Pump Equipment (applicable to FCU integration)
- RoHS 2.0 (2011/65/EU) — Restriction of Hazardous Substances Compliance
- REACH (EC) No 1907/2006 — Registration, Evaluation, Authorization and Restriction of Chemicals Compliance
Unique Selling Points
- Cross-Flow Optimized Architecture: Industry-first coil tube design specifically engineered for cross-flow fan aerodynamics, achieving superior COP (Coefficient of Performance) compared to generic coil tubes retrofitted into cross-flow systems.
- Full Stainless Steel Construction: End-to-end stainless steel tubing eliminates corrosion-induced failure points common in copper-aluminum hybrid coils, extending service life to 20+ years.
- Customizable Circuit Configuration: Flexible design parameters allow precise thermal capacity matching to specific cross-flow fan models and operating conditions.
- Low-GWP Refrigerant Ready: Designed and tested for compatibility with next-generation low Global Warming Potential (GWP) refrigerants including R32 and R290.
- Acoustic Performance: Optimized fin geometry and tube arrangement contribute to noise reduction of 3–5 dBA compared to standard coil configurations.
Technical Support & Customization
Wenzhou Jixing Metal Materials Co., Ltd. offers comprehensive technical support including:
- Custom coil design based on specific thermal load requirements and cross-flow fan specifications
- Thermal performance simulation and CFD (Computational Fluid Dynamics) analysis
- Material certification documentation (Mill Test Reports, Chemical Analysis Certificates)
- On-site installation guidance and performance verification services
- OEM/ODM manufacturing with private labeling capabilities