Stainless Steel Coil Tube (Coiltube) — Louver Fresh Air Treatment System Series
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for integration into louver-type independent fresh air treatment air conditioning systems. Unlike conventional straight-length piping, the coil tube is formed into a continuous helical or serpentine configuration, maximizing surface area within a compact volumetric footprint. This geometric advantage is critical in heat exchange applications where thermal efficiency and space utilization must be simultaneously optimized.
The product has been extensively validated through numerical simulation and thermodynamic analysis of louver coil tube fresh air treatment systems. Computational Fluid Dynamics (CFD) modeling and thermodynamic performance evaluation confirm that the coil tube geometry achieves superior air-side heat transfer coefficients compared to flat-plate or fin-and-tube alternatives, particularly under turbulent flow conditions typical of HVAC air handling units (AHUs).
These coil tubes serve as the primary heat exchange medium in independent fresh air handling units, where they facilitate sensible and latent heat exchange between incoming outdoor air and the refrigerant or hot water circulating within the tube lumen.
2. Material & Properties
The coil tubes are fabricated from austenitic stainless steel grades selected for their exceptional combination of corrosion resistance, thermal conductivity, mechanical strength, and formability. The following material grades are available:
- AISI 304 (UNS S30408) — The standard grade for general HVAC applications, offering excellent resistance to atmospheric corrosion, good weldability, and adequate thermal performance.
- AISI 316L (UNS S31603) — Enhanced grade with molybdenum addition (2.0–3.0% Mo), providing superior resistance to chloride-induced pitting and crevice corrosion, recommended for coastal environments and high-humidity fresh air treatment systems.
- AISI 321 (UNS S32100) — Titanium-stabilized grade (5×C Ti) offering improved resistance to intergranular corrosion at elevated temperatures, suitable for hot water coil applications.
Key Material Properties (AISI 304 Reference):
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Coefficient of Thermal Expansion: 17.3 × 10⁻⁶ /°C (20–100°C)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Tensile Strength: ≥ 515 MPa
- Elongation at Break: ≥ 40%
- Corrosion Resistance: Excellent against atmospheric, industrial, and food-grade environments
- Operating Temperature Range: −196°C to +870°C
3. Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Product Designation | Coiltube — Louver Fresh Air Series | — |
| Tube Outer Diameter (OD) | 6.0 / 8.0 / 10.0 / 12.0 | mm |
| Tube Wall Thickness | 0.5 / 0.6 / 0.8 / 1.0 | mm |
| Coil Pitch (Helical Spacing) | 10 – 50 (customizable) | mm |
| Coil Bundle Length (Straight) | 500 – 3000 | mm |
| Coil Winding Turns | Up to 200 (configurable) | — | Material Grade | AISI 304 / 316L / 321 | — |
| Surface Finish | BA (Bright Annealed) / 2B / No.4 Brushed | — |
| Surface Roughness (Ra) | ≤ 0.8 | μm |
| Maximum Operating Pressure | 1.6 (standard) / 2.5 (reinforced) | MPa |
| Refrigerant Compatibility | R-134a, R-410A, R-32, R-407C, R-404A | — |
| Hot Water Compatibility | Up to 95°C | °C |
| Standards Compliance | ASTM A269, ASTM A213, EN 10216-5 | — |
4. Manufacturing Process
The production of coil tubes follows a rigorous multi-stage process ensuring dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Inspection: Stainless steel strip or seamless tube blank stock is procured from certified mills and subjected to spectroscopic analysis (OES) to verify chemical composition compliance with ASTM A269/A213 specifications.
- Coil Forming (Cold Bending): High-precision CNC coil forming machines shape the tube into the designated helical or serpentine geometry. Forming parameters (bend radius, pitch, feed rate) are controlled to prevent wall thinning below 10% of nominal thickness and to avoid material strain hardening that could compromise subsequent performance.
- Solid Solution Annealing: Formed coils undergo solution annealing at 1050–1150°C in a protective atmosphere (hydrogen or argon) to relieve cold-work stresses, restore full austenitic microstructure, and achieve maximum corrosion resistance and ductility.
- Pickling & Passivation: Post-annealing, coils are pickled in dilute nitric-hydrofluoric acid solutions to remove surface oxide scale, followed by passivation treatment to establish a stable chromium oxide passive film (Cr₂O₃) on the surface.
- Precision Welding (if applicable): End joints or connection points are welded using TIG (Tungsten Inert Gas) welding with argon shielding gas, ensuring full penetration welds with no oxide inclusion or porosity defects.
- Pressure Testing & Leak Detection: Each coil tube assembly undergoes hydrostatic pressure testing at 1.5× the maximum design operating pressure (typically 2.4–3.75 MPa) for a minimum hold time of 30 minutes. Helium leak detection (sensitivity: 1×10⁻⁹ Pa·m³/s) is performed on critical applications.
- Final Dimensional Inspection: Coordinate Measuring Machine (CMM) inspection verifies coil pitch uniformity, OD tolerance (±0.1 mm), and overall geometry. Surface roughness is measured using contact profilometry.
5. Applications
The coil tube product is primarily engineered for the following application domains:
- Louver Fresh Air Treatment Systems: As validated by numerical simulation and thermodynamic analysis, the coil tube serves as the core heat exchange element in independent fresh air handling units equipped with adjustable louver panels. The helical geometry promotes turbulent flow on the air side, enhancing the Nusselt number (Nu) and overall heat transfer coefficient (U-value) by 20–35% compared to straight tube configurations.
- Commercial & Industrial HVAC Systems: Chilled water cooling coils and hot water heating coils in air handling units for commercial buildings, hospitals, data centers, and manufacturing facilities.
- Food & Pharmaceutical Processing: Sanitary-grade fresh air systems in cleanroom environments where stainless steel's non-reactive surface prevents microbial contamination.
- Marine & Coastal HVAC: 316L grade coil tubes for fresh air systems in offshore platforms, ships, and coastal installations exposed to high-chloride environments.
- Agricultural & Cold Storage: Fresh air pre-conditioning coils in cold storage facilities and agricultural drying systems.
6. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring product reliability and regulatory compliance:
- ISO 9001:2015 — Quality Management System certification covering the entire design, manufacturing, and testing process chain.
- ISO 14001:2015 — Environmental Management System certification, demonstrating responsible manufacturing practices and sustainable resource utilization.
- CE Marking — European Conformity certification confirming compliance with relevant EU directives including the Pressure Equipment Directive (PED 2014/68/EU) for pressure-containing components.
- EN 10204 3.1 — Material Test Report certification providing full traceability of chemical composition, mechanical properties, and heat treatment records.
- ASTM A269 / A213 Compliance — Product manufactured and tested in accordance with American Society for Testing and Materials standards for welded and seamless austenitic stainless steel tubing.
- HACCP / FDA Compliance — Available for food-grade applications, ensuring the coil tube surface meets food safety standards for contact with food processing environments.
7. Unique Selling Points
Thermodynamically Optimized Geometry: The coil tube design has been rigorously validated through numerical simulation of louver fresh air treatment systems, with CFD-confirmed enhancement of heat transfer performance and pressure drop characteristics under real-world operating conditions.
- Superior Surface-to-Volume Ratio: The helical coil geometry maximizes heat transfer surface area within a compact installation envelope, reducing equipment footprint by up to 40% compared to equivalent-capacity flat coil alternatives.
- Enhanced Turbulence Promotion: The curved tube geometry naturally induces secondary flow patterns (Dean vortices) on the air side, increasing the convective heat transfer coefficient without the need for additional fins or turbulators.
- Corrosion-Free Longevity: Austenitic stainless steel construction eliminates the risk of internal corrosion and tube failure, extending service life to 20+ years under normal operating conditions.
- Customizable Configuration: Coil pitch, OD, wall thickness, and total turns are fully customizable to match specific system design requirements, enabling optimal integration with various AHU configurations.
- Low Maintenance: The smooth, passivated stainless steel surface resists fouling and biofilm accumulation, reducing cleaning frequency and maintaining stable thermal performance over the product lifecycle.