Stainless Steel Coil Tube (Coiltube) — Fan Coil Unit Flow Field Optimization Series
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Reference No.: 350
Category: Technical Literature & Engineering Reference
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component designed primarily for use in Fan Coil Units (FCUs) within HVAC (Heating, Ventilation, and Air Conditioning) systems. This product line has been developed in conjunction with advanced flow field optimization research, integrating both Computational Fluid Dynamics (CFD) numerical simulation and experimental validation to achieve superior thermal-hydraulic performance.
The coil tube is manufactured in a continuous helical or serpentine coil configuration, enabling compact heat exchange geometries with high surface-area-to-volume ratios. The design philosophy draws upon rigorous academic study of internal and external flow characteristics, pressure drop minimization, and heat transfer enhancement within fan coil unit assemblies. This product represents the intersection of metallurgical engineering excellence and fluid mechanics optimization, delivering a coil tube that maintains structural integrity under cyclic thermal loading while maximizing convective heat transfer efficiency.
2. Material & Properties
2.1 Base Alloy Composition
The coil tube is fabricated from high-purity austenitic stainless steel, typically conforming to the following standard grades:
- ASTM A269 / A270 Type 304 (UNS S30400): General-purpose corrosion-resistant grade with excellent formability and weldability.
- ASTM A269 / A270 Type 316 (UNS S31600): Enhanced pitting and crevice corrosion resistance due to 2.0–3.0% Molybdenum (Mo) addition, suitable for aggressive fluid environments.
- ASTM A269 / A270 Type 316L (UNS S31603): Low-carbon variant (≤0.03% C) for superior weldability and resistance to intergranular corrosion.
2.2 Mechanical Properties (Annealed Condition)
| Property | Type 304 | Type 316 | Test Standard |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa | ≥ 515 MPa | ASTM A370 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa | ASTM A370 |
| Elongation (A50mm) | ≥ 40% | ≥ 40% | ASTM A370 |
| Hardness (HBW) | ≤ 201 | ≤ 201 | ASTM E10 |
2.3 Physical & Thermal Properties
| Property | Value |
|---|---|
| Density (ρ) | 7,900 kg/m³ (25°C) |
| Thermal Conductivity (λ) | 16.3 W/(m·K) at 25°C; 25.1 W/(m·K) at 100°C |
| Specific Heat Capacity (cp) | 500 J/(kg·K) at 25°C |
| Coefficient of Thermal Expansion (α) | 17.3 × 10⁻⁶ /K (25–300°C) |
| Maximum Service Temperature | 870°C (Type 304); 870°C (Type 316) |
| Minimum Service Temperature | Cryogenic (down to −196°C / LN₂ temperature) |
2.4 Corrosion Resistance
The passive chromium oxide (Cr₂O₃) film formed on the stainless steel surface provides exceptional resistance against atmospheric corrosion, aqueous environments, and many chemical media. Type 316 grades additionally exhibit superior resistance to chloride-induced pitting and crevice corrosion, making them ideal for coastal applications, chemical processing, and food-grade fluid handling.
3. Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4") – 50.8 mm (2") | ASTM A269 / A270 |
| Wall Thickness | 0.50 mm – 3.00 mm | ASTM A269 / A270 |
| Coil Pitch (Helical Spacing) | 8 mm – 25 mm (configurable) | Custom / OEM |
| Coil Diameter (Bundle) | 50 mm – 300 mm | Custom / OEM |
| Tube Length per Coil | 1 m – 50 m (continuous) | — |
| Surface Finish | No. 4 Brushed / BA (Bright Annealed) / Electropolished | ASTM A479 / A967 |
| End Treatment | Plain End / Beveled / Threaded / Flanged | ASME B1.20.1 |
| Pressure Rating (Design) | Up to 2.5 MPa (363 psi) at 200°C | ASME B31.5 |
| Tolerance on OD | ± 0.10 mm (± 0.5%) | ASTM A269 |
| Tolerance on Wall Thickness | ± 0.05 mm (± 5%) | ASTM A269 |
| Maximum Flow Velocity (Internal) | ≤ 4.0 m/s (optimized for laminar-to-turbulent transition) | CFD-validated |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Procurement: Hot-rolled stainless steel coil (HR coil) is sourced from certified mills with full material traceability (Heat Number, Mill Test Certificate per EN 10204 Type 3.1).
- Cold Drawing / Cold Rolling: The HR coil is cold-drawn through sequential die sets to achieve precise OD and wall thickness tolerances. This process induces beneficial work hardening and grain refinement while maintaining the austenitic microstructure.
- Intermediate Annealing: Periodic solution annealing at 1050–1100°C followed by rapid quenching relieves accumulated cold work, restores ductility, and re-establishes the passive Cr₂O₃ surface film.
- Precision Coiling: The drawn tube is formed into helical coils using CNC-controlled coiling machines. The coiling geometry is optimized based on CFD simulation data to ensure uniform flow distribution and minimize pressure drop across the coil bundle.
- Final Annealing & Pickling: Post-coiling annealing at 1040–1100°C eliminates residual stresses introduced during forming. Subsequent acid pickling and passivation remove scale and contaminants, restoring optimal corrosion resistance.
- Surface Finishing: Depending on application requirements, the coil tube undergoes electropolishing (ASTM A967), mechanical brushing, or bright annealing (BA) to achieve the specified surface roughness (Ra ≤ 0.4 μm for electropolished finish).
- Quality Inspection: Each production lot undergoes comprehensive testing including dimensional verification, hydrostatic pressure testing, spectrometric chemical analysis, and non-destructive testing (NDT).
4.2 Flow Field Optimization Integration
A distinguishing feature of this coil tube product is the incorporation of flow field optimization methodology derived from advanced numerical and experimental research on fan coil units. The coiling geometry, pitch, and bundle arrangement are designed to achieve:
- Uniform Air Distribution: CFD-optimized coil geometry ensures even airflow across the entire heat exchange surface, eliminating dead zones and flow maldistribution.
- Reduced Pressure Drop: Smooth internal surfaces and optimized bend radii minimize frictional losses, reducing fan power consumption by 10–15% compared to conventional coil designs.
- Enhanced Nusselt Number (Nu): The helical geometry induces secondary Dean vortices that promote turbulent mixing, increasing the internal convective heat transfer coefficient.
- Minimized Condensate Retention: Optimized coil pitch and inclination angles facilitate efficient condensate drainage, preventing waterlogging and subsequent heat transfer degradation.
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCUs): Core heat exchange element in commercial and residential HVAC systems, providing both heating and cooling capacity through forced convection.
- Chilled Water Systems: Integration with central chilled water plants for precise temperature control in offices, hospitals, hotels, and industrial facilities.
- Cleanroom HVAC: Electropolished coil tubes for pharmaceutical, semiconductor, and biotechnology cleanroom environments requiring ultra-low particulate and microbial contamination.
- Food & Beverage Processing: Sanitary-grade coil tubes for refrigeration coils in food storage, pasteurization, and brewing applications (FDA-compliant, 3-A Sanitary Standards).
- Marine & Offshore HVAC: Type 316L coil tubes resistant to saltwater corrosion for shipboard and offshore platform climate control systems.
5.2 Secondary Applications
- Refrigeration condenser and evaporator coils
- Industrial heat exchangers (shell-and-tube, plate-fin)
- Automotive HVAC components
- Solar thermal collector tubes
- Cryogenic fluid transfer lines
- Medical device fluid circuits
6. Quality Certifications & Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent manufacturing quality |
| ISO 14001:2015 | Environmental Management System certification |
| ISO/IEC 17025 | Testing and Calibration Laboratory competence |
| ASTM A269 / A270 | Standard Specification for Seamless Austenitic Stainless Steel Tubing/Pipes |
| EN 10217-7 | European standard for seamless stainless steel tubes for technical uses |
| JIS G3459 | Japanese Industrial Standard for austenitic stainless steel seamless tubes |
| ASME B31.5 | Pressure Piping — Process Piping design and code compliance |
| EN 10204 Type 3.1 | Material Test Certificate — Inspection Report with specific values |
| 3-A Sanitary Standards | Food and dairy industry sanitary design requirements |
| NACE MR0175 / ISO 15156 | Materials for use in H₂S-containing environments (if applicable) |
7. Unique Selling Points
This coil tube product distinguishes itself through the following value propositions:
- CFD-Validated Geometry: Coil pitch, bundle arrangement, and internal flow characteristics are optimized through rigorous Computational Fluid Dynamics (CFD) simulation and experimental validation, ensuring peak thermal-hydraulic performance in fan coil unit applications.
- Superior Energy Efficiency: Reduced pressure drop (10–15% improvement) translates directly to lower fan motor power consumption, contributing to overall system COP (Coefficient of Performance) enhancement and reduced operational carbon footprint.
- Full Material Traceability: Every coil tube batch is accompanied by a complete material traceability chain from mill heat number through final product identification, ensuring compliance with stringent regulatory and quality assurance requirements.
- Customizable Geometries: Flexible manufacturing capability allows OEM-specific coil configurations (pitch, diameter, length, end treatment) tailored to individual fan coil unit designs and installation constraints.
- Extended Service Life: The combination of high-grade austenitic stainless steel, optimized surface finish, and proper passive