Stainless Steel Coil Tube — Fan Coil Unit Heat Exchanger Grade
1. Product Overview
The Stainless Steel Coil Tube (Product No. 830) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous coil tube specifically designed for integration into fan coil unit (FCU) heat exchangers and similar thermal management systems. Unlike conventional straight-section tubing, coil tubes are formed into a continuous helical or serpentine configuration, providing a significantly greater surface-to-volume ratio and superior heat transfer efficiency within a compact envelope.
This product line has been optimized through advanced computational methods, including Genetic Algorithm (GA) optimization design, which enables the systematic refinement of coil geometry parameters — including coil diameter, pitch, tube wall thickness, and cross-sectional profile — to achieve maximum thermal performance while minimizing pressure drop and material consumption. The GA-based optimization framework evaluates thousands of design permutations to identify Pareto-optimal configurations that balance heat exchange capacity, flow resistance, mechanical integrity, and manufacturing feasibility.
Stainless steel coil tubes from Wenzhou Jixing Metal Materials are widely deployed in HVAC (Heating, Ventilation, and Air Conditioning), industrial process cooling, refrigeration systems, and specialty thermal applications where corrosion resistance, long service life, and high thermal conductivity are critical requirements.
2. Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of mechanical strength, corrosion resistance, and thermal stability across a broad operating temperature range.
2.1 Material Grades
- 304 (UNS S30400 / 1.4301): The most widely used austenitic stainless steel, offering excellent general corrosion resistance, weldability, and formability. Suitable for ambient to moderately aggressive environments.
- 316 (UNS S31600 / 1.4401): Enhanced resistance to chlorides and pitting corrosion due to the addition of 2–3% molybdenum (Mo). Preferred for marine, chemical processing, and coastal applications.
- 316L (UNS S31603 / 1.4404): Low-carbon variant of 316 with carbon content ≤ 0.03%, providing superior resistance to intergranular corrosion during welding and high-temperature exposure.
2.2 Key Material Properties (Typical Values for Grade 304)
| Property | Symbol | Value | Units | Test Standard |
|---|---|---|---|---|
| Tensile Strength (Ultimate) | σb | ≥ 520 | MPa | ASTM A269 / GB/T 12771 |
| Yield Strength (0.2% offset) | σ0.2 | ≥ 205 | MPa | ASTM A269 / GB/T 12771 |
| Elongation (at break) | A | ≥ 40 | % | ASTM A269 |
| Thermal Conductivity (at 20°C) | k | 16.3 | W/(m·K) | ASTM E153 |
| Specific Heat Capacity (at 20°C) | cp | 500 | J/(kg·K) | — |
| Density (at 20°C) | ρ | 7.93 | g/cm³ | — |
| Linear Thermal Expansion Coefficient (20–100°C) | α | 17.3 | × 10⁻⁶ /K | ASTM E228 |
| Maximum Operating Temperature | Tmax | 870 | °C | — |
| Corrosion Potential (in 3.5% NaCl, 35°C) | Ecorr | −0.2 to −0.1 | V vs. SCE | ASTM G5 |
2.3 Chemical Composition (Grade 304, wt%)
| Element | C | Si | Mn | P | S | Cr | Ni | N |
|---|---|---|---|---|---|---|---|---|
| Range | ≤ 0.08 | ≤ 0.75 | ≤ 2.00 | ≤ 0.045 | ≤ 0.030 | 18.0–20.0 | 8.0–10.5 | ≤ 0.10 |
3. Specifications
The coil tube is available in a comprehensive range of dimensional configurations to accommodate diverse heat exchanger design requirements. All dimensions are compliant with ASTM A269/A269M (Standard Specification for Seamless and Wrought Stainless Steel Tube, Boiler, Heat-Exchanger, and Condenser Service) and GB/T 12771 (Chinese National Standard for Welded Stainless Steel Tubes for General Purposes).
3.1 Dimensional Specifications
| Parameter | Range / Value | Unit | Tolerance |
|---|---|---|---|
| Outer Diameter (OD) | 6.0 – 25.4 | mm | ± 0.10 |
| Wall Thickness | 0.4 – 1.5 | mm | ± 10% of nominal |
| Coil Bending Diameter | 20 – 200 | mm | ± 2% |
| Coil Pitch (Center-to-Center) | 3 – 50 | mm | ± 0.5 |
| Coil Length (per coil) | Up to 12,000 | mm | — |
| Surface Finish (Roughness Ra) | ≤ 0.8 (inner); ≤ 1.6 (outer) | μm | — |
| End Condition | Plain, Beveled, or Flanged | — | Per drawing |
| Coil Winding Direction | CW (Clockwise) or CCW (Counter-Clockwise) | — | — |
| Delivery Condition | Annealed (Solution Treated) | — | — |
3.2 Common Coil Tube Configurations (Selected)
| Model Code | OD (mm) | Wall (mm) | Bend Diameter (mm) | Pitch (mm) | Material | Application |
|---|---|---|---|---|---|---|
| JX-CT-0806 | 8.0 | 0.6 | 40 | 8 | 304 | Residential FCU |
| JX-CT-1006 | 10.0 | 0.6 | 50 | 10 | 304 | Commercial HVAC |
| JX-CT-1208 | 12.7 | 0.8 | 60 | 12 | 316L | Industrial Process |
| JX-CT-1610 | 15.9 | 1.0 | 80 | 15 | 316L | Marine Refrigeration |
| JX-CT-2012 | 19.1 | 1.2 | 100 | 20 | 316L | Chemical Processing |
4. Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage manufacturing workflow, integrating traditional metallurgical expertise with modern computational optimization techniques.
4.1 Process Flow
- Raw Material Selection & Incoming Inspection: Cold-rolled stainless steel strip is sourced from certified mills and subjected to spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with the specified grade.
- Strip Preparation: The strip is slit to the required width, edge-trimmed, and subjected to surface cleaning and pickling to remove mill scale and surface contaminants.
- Tube Forming (Roll Forming): Precision roll-forming dies progressively bend the strip into a tubular cross-section. The forming process is monitored for dimensional accuracy and uniform wall thickness distribution.
- Welding (TIG — Tungsten Inert Gas): The formed tube is welded along its longitudinal seam using high-purity argon (Ar) shielding gas to prevent oxidation. Weld bead height is controlled to ≤ 0.05 mm internal protrusion to ensure smooth internal flow characteristics.
- Coil Forming (Helical Bending): The straight tube is mechanically coiled using a CNC-controlled bending machine. The bending process is guided by GA-optimized parameters (bend radius, pitch, speed) to minimize residual stress and prevent ovality. The coil geometry is validated against finite element analysis (FEA) predictions to ensure uniform deformation.
- Heat Treatment (Annealing): The coiled tube assembly undergoes solution annealing at 1050–1100°C followed by controlled cooling. This step relieves residual stresses from forming and welding, restores full austenitic microstructure, and ensures the material meets specified mechanical properties.
- Pickling & Passivation: The annealed tube is immersed in a mixed acid bath (HNO₃/HF or HNO₃/HCl) to remove oxide scale, followed by passivation treatment to enhance the passive chromium oxide (Cr₂O₃) film and improve corrosion resistance.
- Quality Inspection & Testing: Comprehensive inspection protocols are applied, including dimensional measurement, hydrostatic pressure testing, leak testing (helium or nitrogen), and visual examination of weld seams and coil geometry.
- Packaging & Dispatch: Finished coil tubes are packaged in protective wrapping, secured on wooden pallets or steel drums, and prepared for shipment with accompanying material test certificates (MTC — Material Test Certificate).
4.2 Genetic Algorithm Optimization Integration
A distinguishing feature of this product line is the application of Genetic Algorithm (GA) optimization in the design phase. The GA framework operates as follows:
- Objective Functions: Maximize heat transfer coefficient (U-value); minimize pressure drop (ΔP); minimize material cost; minimize coil weight.
- Decision Variables: Coil diameter (D), coil pitch (P), tube outer diameter (do), wall thickness (t), number of tube passes (N), tube layout pattern.
- Constraints: Maximum allowable stress under operating pressure; minimum bend radius (≥ 3 × OD); manufacturing feasibility limits; weight restrictions.
- Algorithm Parameters: Population size of 100–200 individuals; crossover rate of 0.85; mutation rate of 0.02; convergence criterion of 50 generations without improvement.
This computational optimization ensures that each coil tube configuration is engineered for optimal thermal-hydraulic performance, reducing energy consumption by an estimated 15–25% compared to conventionally designed heat exchangers.
5. Applications
Stainless steel coil tubes from Wenzhou Jixing Metal Materials Co., Ltd. find extensive application across multiple industrial and commercial sectors:
5.1 Primary Applications
- Fan Coil Units (FCUs): The primary application domain. Coil tubes serve as the