Stainless Steel Coil Tube for Fan Coil Unit (FCU) Heat Exchangers
Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd., specifically designed for use as the core heat transfer element in Fan Coil Unit (FCU) Air Conditioners. This coil tube product represents the critical structural and functional backbone of the evaporator and condenser heat exchangers employed in commercial and residential HVAC (Heating, Ventilation, and Air Conditioning) systems. The coil tube is formed into a serpentine or spiral configuration to maximize the surface-area-to-volume ratio, thereby optimizing thermal exchange efficiency between the refrigerant or chilled water circulating within the tube and the ambient air drawn across the external finned surface by the fan assembly.
As a fundamental component in modern climate control infrastructure, the coil tube directly influences the overall energy efficiency, thermal performance, and service life of the complete fan coil air conditioning system. The design philosophy adheres to the principles outlined in industry-standard heat exchanger literature, emphasizing uniform flow distribution, minimal pressure drop, and maximum heat transfer coefficient.
Material & Properties
The coil tube is fabricated from high-grade stainless steel, selected for its superior combination of corrosion resistance, mechanical strength, and thermal conductivity. The following material specifications define the baseline properties:
- Base Material: Austenitic Stainless Steel conforming to ASTM A269 / ASTM A312 or EN 10216-5 standards
- Common Grades: SUS304 (1.4301), SUS316 (1.4401), SUS316L (1.4404)
- Chromium (Cr) Content: 18.0%–20.0% (SUS304) / 16.0%–18.0% (SUS316)
- Nickel (Ni) Content: 8.0%–10.5% (SUS304) / 10.0%–14.0% (SUS316)
- Molybdenum (Mo) Content: 2.0%–3.0% (SUS316 only)
- Carbon (C) Maximum: 0.08% (SUS304) / 0.03% (SUS316L)
- Thermal Conductivity: 16.3 W/(m·K) at 300 K
- Specific Heat Capacity: 460 J/(kg·K) at 20°C
- Density: 8.00 g/cm³
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and chemical corrosion; SUS316 grade offers superior pitting and crevice corrosion resistance due to molybdenum addition
- Non-magnetic: Austenitic microstructure ensures non-magnetic properties
- Hygienic Compliance: Suitable for potable water and food-grade applications
Specifications
| Parameter | Specification / Value |
|---|---|
| Tube Outer Diameter (OD) | 6.0 mm / 7.0 mm / 8.0 mm / 9.52 mm / 10.0 mm / 12.0 mm / 15.88 mm |
| Wall Thickness (WT) | 0.5 mm – 1.5 mm (typical range) |
| Coil Tube Length | Customized; typical range 3.0 m – 15.0 m per continuous length |
| Coil Pitch (Fin Spacing) | 1.6 mm – 2.5 mm (adjustable per thermal design requirement) |
| Number of Rows | 2 to 6 rows (configurable per BTU capacity requirement) |
| Heat Exchanger Face Dimensions | Standard: 400×400 mm, 500×500 mm, 600×600 mm; Custom sizes available |
| Operating Temperature Range | -40°C to +250°C |
| Maximum Operating Pressure | 1.6 MPa (standard) / up to 4.0 MPa (reinforced configuration) |
| Refrigerant Compatibility | R-22, R-407C, R-410A, R-134a, R-32, R-1234yf |
| Chilled Water Flow Rate | 0.5 – 8.0 L/min (dependent on coil size and configuration) |
| Fin Material | Aluminum (Al 1100 / Al 3003) or Copper (Cu C1100) |
| Fin Treatment | Hydrophilic coating (optional) for enhanced condensation performance |
| Surface Finish | 2B / BA (Bright Annealed) / Pickled |
| End Treatment | Deburred, chamfered, or flared per customer specification |
| Coating / Passivation | Passivated per ASTM A967; optional PTFE anti-corrosion coating |
Manufacturing Process
The production of the stainless steel coil tube for fan coil unit heat exchangers follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, structural integrity, and thermal performance:
- Raw Material Procurement & Inspection: Stainless steel seamless tubes or welded tubes are sourced from certified mills and subjected to incoming quality inspection including chemical composition analysis (OES / Spectrometry), dimensional verification, and mechanical property testing (tensile strength, hardness, impact testing).
- Cutting & Preparation: Tubes are precision-cut to required lengths using CNC tube cutting machinery with tolerance control within ±0.1 mm. End surfaces are deburred and chamfered to prevent turbulence and flow restriction.
- Bending & Forming: Tubes are formed into the serpentine coil pattern using CNC tube bending machines. The bending process employs controlled tooling radii to prevent tube collapse, ovality, or wall thinning. Minimum bend radius is maintained at 3× the tube OD to ensure structural integrity.
- Fin Insertion: Aluminum or copper fins are inserted into the formed tube array using automated fin-stacking and insertion equipment. Fin alignment and spacing are controlled to within ±0.05 mm to ensure uniform airflow and optimal heat transfer.
- Hydroforming / Brazing: The coil assembly is secured through vacuum brazing (for copper fin configurations) or mechanical crimping/expansion (for aluminum fin configurations). Brazing is performed under vacuum or inert gas (Nitrogen, N₂) atmosphere at temperatures between 600°C–650°C to prevent oxidation.
- Passivation & Surface Treatment: The finished coil tube undergoes passivation treatment per ASTM A967 to enhance the chromium oxide protective layer. Optional hydrophilic coating is applied to fins to promote uniform condensate drainage and reduce frosting in low-temperature applications.
- Pressure & Leak Testing: Each heat exchanger coil assembly undergoes 100% pressure testing at 1.5× the maximum operating pressure, followed by helium leak detection or electronic bubble testing to verify hermetic integrity. Acceptance criteria: zero leakage at test pressure maintained for a minimum of 5 minutes.
- Final Inspection & Packaging: Finished products undergo dimensional inspection, visual examination, and performance verification. Coils are packaged with protective end caps, desiccant packets, and moisture-barrier wrapping for transport and storage.
Applications
The stainless steel coil tube heat exchanger is integral to a wide range of HVAC systems and industrial applications:
- Commercial HVAC Systems: Primary heat exchanger component in fan coil units for office buildings, hotels, hospitals, shopping malls, and educational institutions.
- Residential Climate Control: Used in ducted and ductless mini-split air conditioning systems for high-end residential applications.
- Industrial Process Cooling: Applied in precision temperature control for manufacturing processes including semiconductor fabrication, pharmaceutical production, and food processing.
- Refrigeration Systems: Employed as evaporator coils in commercial refrigeration units, cold storage facilities, and display cases.
- Heat Recovery Systems: Utilized in air-to-air and air-to-water heat recovery units for energy-efficient building ventilation.
- Marine & Offshore Applications: SUS316 grade coil tubes provide corrosion resistance in marine HVAC systems exposed to salt-laden environments.
- Cleanroom & Laboratory HVAC: Hygienic stainless steel construction meets cleanroom standards for pharmaceutical and biotechnology facilities.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications to assure product excellence:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and continuous improvement.
- ISO 14001:2015 — Environmental Management System certification demonstrating environmental responsibility in manufacturing operations.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- EN 10204 3.1 Certificate — Material test certificates providing traceable chemical composition and mechanical property data for each production lot.
- CE Marking — Compliance with European Union directives for product safety and performance.
- UL / cUL Listed — Underwriters Laboratories certification for safety compliance in North American markets.
- ASTM Compliance — Materials and testing procedures conform to ASTM A269, ASTM A312, ASTM A967, and ASTM B866 standards.
- ASME Standards — Heat exchanger design and fabrication in accordance with ASME BPV Code (where applicable).
- Material Traceability: Full batch traceability from raw material mill certificate through final product shipment, enabling complete supply chain accountability.
Unique Selling Points
1. Superior Corrosion Resistance: Unlike conventional carbon steel or copper tube alternatives, stainless steel coil tubes provide exceptional longevity in corrosive environments, significantly reducing maintenance frequency and extending service life beyond 15–20 years under normal operating conditions.
2. Hygienic & Food-Grade Compliance: The austenitic stainless steel construction meets FDA and EHEDG standards, making these coils suitable for food processing, pharmaceutical, and healthcare applications where sanitary requirements are paramount.
3. Precision Engineering for Optimal Heat Transfer: CNC-controlled bending and fin insertion ensure uniform coil geometry, minimizing flow maldistribution and maximizing the overall heat transfer coefficient (U-value) of the complete heat exchanger assembly.
4. Wide Refrigerant Compatibility: Engineered to accommodate next-generation low-GWP (Global Warming Potential) refrigerants including R-32, R-410A, and R-1234yf, ensuring future-proof design aligned with international environmental regulations.
5. Customizable Configuration: Flexible design parameters (tube OD, wall thickness, fin pitch, row count, face dimensions) allow tailoring to specific BTU capacity, airflow, and pressure drop requirements for diverse application scenarios.
6. Full Traceability & Certification: Comprehensive quality documentation and third-party certifications provide assurance for global market compliance and customer confidence.
Technical Notes & Design Considerations
When integrating the stainless steel coil tube heat exchanger into a fan coil air conditioning system, the following engineering considerations should be observed:
- Flow Balance: Ensure even refrigerant or water distribution across all coil rows to prevent localized overheating or underutilization of heat transfer surface.
- Pressure Drop: Account for pressure drop across the coil tube circuit when sizing pumps, compressors, and control valves. Typical pressure drop ranges from 0.5 to 3.0 kPa depending on flow rate and configuration.
- Condensate Management: Design proper drainage slopes and condensate pan integration to prevent water accumulation and microbial growth.
- Thermal Expansion: Allow for differential thermal expansion between the stainless steel tube and aluminum fins through appropriate mechanical clearance or flexible connections.
- Insulation: Apply closed-cell foam insulation to the coil casing to prevent condensation on external surfaces and minimize heat loss to the environment.