Stainless Steel Coil Tube for Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed specifically for use in Fan Coil Unit (FCU) systems within commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) applications. This product represents a critical heat exchanger component whose geometric configuration and material integrity directly influence thermal performance, hydraulic efficiency, and long-term service reliability.
Based on comprehensive Computational Fluid Dynamics (CFD) analysis of internal flow fields within fan coil unit coil assemblies, the coil tube geometry has been optimized to minimize flow maldistribution, reduce pressure drop across the coil circuit, and enhance overall heat transfer coefficients. The design philosophy integrates laminar-to-turbulent transition management, uniform flow distribution across parallel tubes, and structural resistance to thermal cycling fatigue.
Material & Properties
The coil tube is fabricated from high-grade stainless steel alloys selected for their corrosion resistance, thermal conductivity, and mechanical durability in aggressive indoor air environments.
- Primary Material Grades: AISI 304 (UNS S30408), AISI 316L (UNS S31603), and Duplex 2205 (UNS S31803) are available depending on service environment requirements.
- Chemical Composition (AISI 304): Carbon ≤ 0.08%, Chromium 18.0–20.0%, Nickel 8.0–10.5%, Manganese ≤ 2.0%, Silicon ≤ 1.0%, Sulfur ≤ 0.030%.
- Chemical Composition (AISI 316L): Carbon ≤ 0.030%, Chromium 16.5–18.5%, Nickel 10.0–14.0%, Molybdenum 2.0–3.0%, Manganese ≤ 2.0%.
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C for AISI 304; 13.5–16.2 W/(m·K) for AISI 316L.
- Specific Heat Capacity: 478–502 J/(kg·K).
- Density: 7.93 g/cm³ (AISI 304); 8.03 g/cm³ (AISI 316L).
- Operating Temperature Range: −196°C to +870°C (continuous service).
- Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and intergranular corrosion in chloride-containing environments.
Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 9.52 mm (⅜"), 12.7 mm (½"), 15.88 mm (⅝") | ±0.1 mm |
| Wall Thickness | 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm | ±0.05 mm |
| Inner Diameter (ID) | 8.52 mm, 11.5 mm, 14.28 mm | ±0.1 mm |
| Coil Pitch (Center-to-Center Spacing) | 12 mm, 15 mm, 19 mm, 25 mm | ±0.5 mm |
| Tube Length per Coil | 500 mm to 3,000 mm | ±5 mm |
| Number of Rows | 2-row, 4-row, 6-row, 8-row configurations | — |
| Surface Finish (Internal) | Electropolished, Ra ≤ 0.4 μm | — |
| Surface Finish (External) | 2B / BA (Bright Annealed), Ra ≤ 0.8 μm | — |
| Maximum Operating Pressure | 1.6 MPa (232 psi) | — |
| Hydrostatic Test Pressure | 2.4 MPa (348 psi) | — |
| Heat Transfer Coefficient (Water Side) | 3,500–5,500 W/(m²·K) | — |
| Pressure Drop (per Row) | ≤ 150 Pa @ nominal flow velocity | — |
| Standard Lengths (Coil Assembly) | 600 mm, 900 mm, 1,200 mm, 1,500 mm, 1,800 mm | ±3 mm |
| Connection Type | Flared, Threaded (M14, M18), or Brazed | — |
| Weight (per 1 m coil run) | 0.12–0.28 kg (depending on OD and wall thickness) | — |
Manufacturing Process
- Raw Material Inspection: Incoming stainless steel coils are verified for chemical composition (via Optical Emission Spectrometry, OES), mechanical properties, and surface quality in accordance with ASTM A240/A270 standards.
- Coil Slitting and Leveling: The master coil is slit to precise width using high-speed slitting lines, followed by tension leveling to eliminate residual stress and ensure flatness within ±0.1 mm/m.
- Tube Forming: Continuous roll-forming or push-bending processes convert flat strip into seamless tubes with uniform wall thickness. The forming rollers are precision-ground to maintain dimensional accuracy throughout production runs.
- Welding (for welded configurations): High-frequency induction welding (HFW) or orbital TIG (Tungsten Inert Gas) welding is employed. Internal weld bead dressing ensures smooth flow surfaces and eliminates turbulence-inducing imperfections identified through CFD modeling.
- Coiling and Pitch Formation: Tubes are mechanically coiled to specified pitch dimensions using CNC-controlled bending machines. The coiling process is validated against CFD-optimized flow distribution models to ensure uniform fluid entry across all parallel passages.
- Heat Treatment: Solution annealing at 1,050–1,100°C followed by controlled water quenching eliminates cold-work hardening, restores full corrosion resistance, and achieves the required soft temper (typically HV ≤ 200).
- Surface Finishing: Electropolishing of internal surfaces reduces roughness to Ra ≤ 0.4 μm, minimizing friction losses and fouling potential. External surfaces receive 2B or BA finish for aesthetic and corrosion performance.
- Quality Inspection: Each coil assembly undergoes hydrostatic pressure testing, dimensional verification using coordinate measuring machines (CMM), visual inspection for surface defects, and flow balance testing to confirm CFD-predicted performance parameters.
Applications
- Fan Coil Units (FCUs): Primary application — serves as the chilled water or hot water heat exchanger in ceiling-mounted, wall-mounted, and floor-standing FCU systems for commercial buildings, hotels, hospitals, and office complexes.
- Commercial HVAC Systems: VAV (Variable Air Volume) terminal units, air handling units (AHUs), and constant volume systems requiring high-efficiency coil assemblies.
- Food and Beverage Processing: Hygienic-grade coil assemblies for pasteurization, cooling, and thermal processing equipment where product contact requires FDA-compliant stainless steel.
- Pharmaceutical Manufacturing: Cleanroom HVAC coils and process cooling systems requiring GMP (Good Manufacturing Practice) compliant, cleanable, and corrosion-resistant components.
- Marine and Coastal Environments: HVAC systems in ships, offshore platforms, and coastal facilities where high-chloride environments demand AISI 316L or duplex stainless steel coil tubes.
- Industrial Process Cooling: Precision temperature control systems in electronics manufacturing, data centers, and laboratory environments.
Quality Certifications and Standards
- Material Standards: ASTM A269 (Seamless and Welded Austenitic Stainless Steel Tubing), ASTM A270 (Seamless and Welded Austenitic Stainless Steel Tubing for General Service), EN 10217-7 (Heat-Exchanger and Heat-Sink Tubes).
- Manufacturing Standards: ISO 9001:2015 (Quality Management Systems), ISO 14001:2015 (Environmental Management Systems).
- Product Testing Standards: ASTM A269/A269M (Hydrostatic Testing), ASTM E10 (Rockwell Hardness Testing), ASTM A923 (Intergranular Corrosion Testing).
- Performance Validation: ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) standards for coil performance rating; CFD simulation validated per ANSI/CFD best practices for internal flow field characterization.
- Industry Certifications: PED (Pressure Equipment Directive 2014/68/EU) for pressure-bearing applications; CE marking for European market compliance.
- Traceability: Full heat-number traceability from raw material mill certificates through final product inspection reports, ensuring complete supply chain documentation.
Unique Selling Points
- CFD-Optimized Geometry: Internal flow field distribution is engineered using Computational Fluid Dynamics analysis to ensure uniform flow across all parallel tubes, reducing bypass flow and enhancing effective heat transfer area utilization by up to 12% compared to conventionally designed coils.
- Ultra-Smooth Internal Surface: Electropolished internal surfaces (Ra ≤ 0.4 μm) minimize hydraulic resistance, reduce fouling accumulation, and maintain stable pressure drop characteristics over extended service life.
- Thermal Cycling Fatigue Resistance: Material selection and heat treatment protocols ensure minimum 100,000 thermal cycles without degradation of mechanical integrity or dimensional stability.
- Modular Configurations: Available in 2-row through 8-row configurations with customizable pitch and tube length to meet specific capacity requirements from 2 kW to 35 kW per unit.
- Extended Service Life: Superior corrosion resistance of austenitic and duplex stainless steel grades ensures 15–25 year design life even in aggressive chemical and high-humidity environments.
- Energy Efficiency: Optimized flow distribution and reduced pressure drop translate to lower pumping power requirements, contributing to overall system COP (Coefficient of Performance) improvement of 5–8%.
Technical Notes
The internal flow field characteristics of the coil tube assembly are critical to Fan Coil Unit performance. CFD analysis reveals that improper coil pitch or tube alignment can create recirculation zones, flow separation, and non-uniform velocity profiles at tube inlets — all of which degrade heat transfer efficiency and increase fan power consumption. Wenzhou Jixing Metal Materials Co., Ltd. employs validated CFD models (using ANSYS Fluent or similar solvers with turbulence models such as k-ε Realizable or k-ω SST) to pre-validate coil geometry before mass production, ensuring that manufactured products achieve predicted thermal and hydraulic performance within ±5% of simulation results.