Small-Diameter Stainless Steel Coil Tube (Fan Coil Unit Application)
Product Overview
The Small-Diameter Stainless Steel Coil Tube, manufactured by Wenzhou Jixing Metal Materials Co., Ltd (Product No. 781), is a precision-engineered coiled tube solution specifically designed for fan coil unit (FCU) applications in HVAC (Heating, Ventilation, and Air Conditioning) systems. This product category addresses the critical engineering challenge of optimizing heat transfer efficiency, minimizing flow resistance, and reducing operational noise in compact thermal exchange systems.
Based on extensive research into the thermohydraulic performance of small-diameter coil tubes, this product line leverages advanced metallurgical formulations and precision forming techniques to deliver superior thermal conductivity while maintaining structural integrity under cyclic thermal and pressure loading conditions. The coil geometry provides a high surface-area-to-volume ratio, making it ideal for compact heat exchanger assemblies where space constraints are paramount.
Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, primarily conforming to the following material grades:
- AISI 304 (UNS S30408): General-purpose grade with excellent corrosion resistance and formability; chromium content ≥18%, nickel content ≥8%.
- AISI 316 (UNS S31603): Enhanced corrosion resistance grade with molybdenum addition (2.0–3.0%), suitable for aggressive chemical environments.
- AISI 321 (UNS S32103): Titanium-stabilized grade for elevated temperature applications, resisting intergranular corrosion.
Key Physical Properties:
- Thermal conductivity: 16.3 W/(m·K) at 20°C
- Density: 8.00 g/cm³
- Thermal expansion coefficient: 17.3 × 10⁻⁶ /°C
- Maximum operating temperature: 870°C (continuous)
- Mechanical strength (tensile): ≥520 MPa (annealed condition)
- Surface finish: BA (Bright Annealed) or 2B finish, Ra ≤ 0.8 μm
Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 6.0 mm – 12.7 mm (1/4" – 1/2") |
| Wall Thickness | 0.5 mm – 1.2 mm |
| Coil Diameter | 150 mm – 500 mm |
| Coil Length per Unit | 3 m – 12 m (configurable) |
| Material Grade | AISI 304 / 316 / 321 |
| Surface Treatment | BA / 2B / Custom Passivation |
| Pressure Rating | ≤ 2.5 MPa (design pressure) |
| Operating Temperature Range | −196°C to +400°C |
| Tolerance on OD | ±0.05 mm |
| Tolerance on Wall Thickness | ±10% |
| Standards Referenced | ASTM A213 / ASTM A269 / GB/T 12771 |
Manufacturing Process
The production of small-diameter stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence:
- Raw Material Selection: Ingot or strip material is sourced from certified mills with full chemical composition verification via Optical Emission Spectroscopy (OES) and Inductively Coupled Plasma (ICP) analysis.
- Piercing & Extrusion: For seamless tube production, round billets are pierced and extruded through precision dies to achieve the target outer diameter and wall thickness.
- Hot Rolling & Annealing: Tubes undergo hot rolling followed by solution annealing at 1050°C – 1150°C in a protective atmosphere furnace to restore ductility and eliminate residual stresses.
- Cold Drawing & Sizing: Precision cold drawing through calibrated dies achieves final dimensional tolerances and improved surface finish quality.
- Coiling: Tubes are coiled using CNC-controlled coiling machines to maintain uniform coil diameter, consistent pitch, and minimal springback distortion.
- Pickling & Passivation: Chemical cleaning with citric acid or nitric-hydrofluoric acid mixtures removes oxide scale, followed by passivation treatment to enhance corrosion resistance.
- Final Inspection: Each coil undergoes dimensional verification, hydrostatic pressure testing, and visual surface inspection.
Applications
The primary application domain for this product is the fan coil unit (FCU) industry, where the coil tube serves as the core heat transfer element. Additional applications include:
- HVAC Systems: Air handling units, chillers, and condenser coils in commercial and residential buildings.
- Automotive Thermal Management: Radiator cores and intercooler assemblies requiring compact heat exchange geometry.
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration equipment.
- Process Industry: Small-bore heat exchangers in chemical processing, pharmaceutical manufacturing, and food processing.
- Power Generation: Condenser tube bundles in distributed energy systems and waste heat recovery units.
Research on heat transfer and flow resistance characteristics of small-diameter coil tubes has demonstrated that reducing tube diameter below 10 mm significantly increases the heat transfer coefficient due to reduced boundary layer thickness, while the coil geometry promotes secondary flow patterns (Dean vortices) that enhance turbulent mixing. However, this comes at the cost of increased pressure drop, necessitating careful engineering optimization of the tube diameter-to-coil-diameter ratio (D/d).
Unique Selling Points
- Optimized Heat Transfer Performance: Small-diameter geometry (6–12.7 mm OD) maximizes surface-area-to-volume ratio, achieving heat transfer coefficients 30–50% higher than conventional larger-bore alternatives.
- Reduced Noise Characteristics: Precision wall thickness control and uniform coil pitch minimize flow-induced vibration and aerodynamic noise, contributing to quieter fan coil unit operation.
- Superior Corrosion Resistance: Austenitic stainless steel matrix with controlled impurity levels (S ≤ 0.03%, P ≤ 0.045%) ensures long service life in humid and chemically aggressive environments.
- Precision Dimensional Control: CNC coiling and cold-drawing processes ensure consistent geometry critical for automated assembly in fan coil unit manufacturing.
- Customizable Configurations: Flexible coil diameter, length, and pitch specifications enable OEM-specific design integration.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains the following quality management certifications and compliance standards:
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- EN 10204 3.1 — Material Test Certificate compliance
- CE Marking — Conformity with European directives
- ASTM International — Material specification compliance (A213, A269, A778)
- GB/T National Standards — Chinese national standard compliance (GB/T 12771, GB/T 14976)
All production batches undergo rigorous quality assurance including: positive material identification (PMI) verification via X-ray Fluorescence (XRF) spectrometry, dimensional metrology using coordinate measuring machines (CMM), hydrostatic pressure testing at 1.5× design pressure, and surface quality assessment per ASTM A967 passivation standards.