Stainless Steel Dry Coil Tube for High-Density Data Center Cooling Systems
Product Overview
The Stainless Steel Dry Coil Tube (SS-DCT) is a precision-engineered coil tube product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Specifically designed for dry air cooling (DAC, Dry Air Cooling) applications in high-density data centers (HDDC, High-Density Data Center), this product represents a critical component in next-generation thermal management infrastructure. The dry coil tube functions as a heat exchange element within rear-door heat exchangers (RDHX, Rear-Door Heat Exchanger) and in-row cooling units (IRCU, In-Row Cooling Unit), enabling efficient removal of server-generated heat without the use of water-based cooling media.
As data center rack densities continue to escalate beyond 30 kW per rack and toward 50–100 kW per rack, traditional air-cooling solutions face diminishing returns. The SS-DCT addresses this challenge by leveraging the inherent thermal conductivity, corrosion resistance, and mechanical durability of stainless steel in a compact coil geometry that maximizes heat transfer area (HTA, Heat Transfer Area) per unit volume. This product is particularly suited for free-cooling (FC) and mixed-mode cooling architectures where dry-bulb temperature differentials are exploited to achieve significant Partial Load Value (PLV) improvements and reduce Power Usage Effectiveness (PUE) metrics.
Material & Properties
The SS-DCT is fabricated from high-grade austenitic stainless steel, selected for its superior combination of thermal performance, corrosion resistance, and long-term structural integrity in demanding data center environments.
Primary Material Grades
- AISI 304 (UNS S30400) — General-purpose grade with excellent corrosion resistance and weldability; suitable for standard data center ambient conditions with relative humidity up to 80%.
- AISI 316 (UNS S31600) — Molybdenum-enhanced grade offering superior resistance to chloride-induced pitting and crevice corrosion; recommended for coastal or industrial data center locations.
- AISI 321 (UNS S32100) — Titanium-stabilized grade providing enhanced resistance to intergranular corrosion at elevated temperatures; ideal for high-temperature supply air configurations.
Mechanical and Thermal Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS, Ultimate Tensile Strength) | ≥ 520 MPa (AISI 304); ≥ 570 MPa (AISI 316) | ASTM A270 / ASTM A269 |
| Yield Strength (0.2% offset) | ≥ 205 MPa | ASTM A270 |
| Elongation (at fracture) | ≥ 40% | ASTM A270 |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) (AISI 304); 16.3 W/(m·K) (AISI 316) | ASTM E153 |
| Thermal Conductivity (at 200°C) | 25.2 W/(m·K) | ASTM E153 |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /°C | ASTM E228 |
| Corrosion Resistance (Salt Spray Test, NSS) | ≥ 1000 hours without rust (AISI 304); ≥ 2000 hours (AISI 316) | ASTM B117 |
| Operating Temperature Range | −40°C to +260°C | — |
| Surface Roughness (Ra) | ≤ 0.8 μm (inner surface); ≤ 1.6 μm (outer surface) | ASTM B534 |
Specifications
The SS-DCT is available in multiple configurations to accommodate varying thermal loads and spatial constraints within data center cooling architectures.
| Parameter | Specification Range | Notes |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm, 8.00 mm, 9.53 mm, 12.70 mm, 15.88 mm | Custom diameters available upon request |
| Wall Thickness | 0.50 mm – 1.50 mm | Thinner walls for enhanced heat transfer; thicker walls for pressure-rated applications |
| Coil Diameter (CD) | 50 mm – 300 mm | Determined by heat exchanger core geometry |
| Coil Length (per tube) | 1.0 m – 15.0 m | Custom lengths to match heat exchanger face area |
| Number of Coils per Unit | 1 – 48 coils | Configurable based on thermal capacity requirements |
| Tube Pitch (transverse) | 15 mm – 40 mm | Optimized for airflow resistance vs. heat transfer balance |
| Tube Pitch (longitudinal) | 15 mm – 40 mm | — |
| Maximum Operating Pressure | 0.15 MPa (air-side, dry coil configuration) | Designed for low-pressure air flow applications |
| Thermal Capacity (per unit) | 5 kW – 80 kW | Dependent on configuration, airflow velocity, and ΔT |
| Airflow Velocity (recommended) | 1.5 m/s – 4.0 m/s | Optimal range for heat transfer coefficient maximization |
| Pressure Drop (air-side) | 50 Pa – 350 Pa | Measured at design airflow velocity |
| Surface Finish | Electropolished (EP) or Passivated | Enhances corrosion resistance and reduces fouling |
| Connection Type | Brazed, Welded, or Flanged | Brazing alloy: Cu-P or Ni-based |
| Standard Length Options | 3 m, 6 m, 9 m, 12 m | Custom lengths available |
Manufacturing Process
The production of the SS-DCT follows a rigorous multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and consistent thermal performance across all units.
Process Flow
- Raw Material Procurement and Inspection: Cold-rolled stainless steel strip or seamless pipe stock is sourced from certified suppliers. Incoming material undergoes Spectrographic Analysis (SA) per ASTM E415 to verify chemical composition, and Hardness Testing per ASTM E18 (Rockwell) to confirm mechanical properties.
- Pipe Forming: For seamless configurations, Tube Milling or ERW (Electric Resistance Welding) processes are employed. For welded configurations, cold-rolled strip is formed into pipe geometry via Roll Forming with precision-welded seams using TIG (Tungsten Inert Gas) Welding per AWS D10.9.
- Coil Bending: Formed tubes are wound into precise coil geometries using CNC-controlled Tube Bending Machines equipped with Die Sets calibrated to the specified coil diameter. Bending is performed at controlled speeds to prevent Work Hardening and Wall Thinning beyond acceptable tolerances (≤ 15% wall reduction at bend apex).
- Heat Treatment: Coiled tubes undergo Solution Annealing at 1050–1150°C followed by rapid water quenching to restore full austenitic microstructure, eliminate residual stresses from forming, and maximize corrosion resistance. This process ensures the material achieves its specified mechanical and corrosion properties.
- Surface Treatment: Tubes receive Acid Pickling (HNO₃ + HF blend) to remove oxide scale, followed by Passivation (HNO₃ or citric acid) to establish a protective chromium oxide layer. Optional Electropolishing (EP) per ASTM A967 further reduces surface roughness to ≤ 0.4 μm Ra.
- Assembly and Brazing: Individual coils are assembled into heat exchanger cores with aluminum or stainless steel fins. Brazing is performed in a Vacuum Brazing Furnace (atmosphere: 10⁻³ mbar or better) or in a Protective Atmosphere Brazing Line (nitrogen with dew point ≤ −60°C) to prevent oxidation and ensure strong, leak-tight joints.
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Quality Control and Testing:
- Dimensional Inspection: CMM (Coordinate Measuring Machine) verification of coil diameter, pitch, and overall dimensions per ASME Y14.5.
- Leak Testing: Helium leak detection (sensitivity: 1 × 10⁻⁹ Pa·m³/s) or pressure decay testing per ASTM F2923.
- Thermal Performance Testing: Verification of heat transfer coefficient (U-value) and pressure drop in a Thermal Performance Test Rig simulating design operating conditions.
- Corrosion Testing: Accelerated Salt Spray Test (ASTM B117) for a minimum of 1000 hours for AISI 304 and 2000 hours for AISI 316.
- Visual Inspection: 100% inspection for surface defects, weld integrity, and finish quality.
- Packaging and Dispatch: Coils are individually wrapped in Anti-Corrosion VCI (Vapor Corrosion Inhibitor) film, placed in protective wooden crates with desiccant packs, and labeled with traceability documentation including Mill Test Certificates (MTC), heat numbers, and inspection reports.
Applications
The SS-DCT is purpose-engineered for thermal management in high-density data center environments, where efficient heat rejection is critical to maintaining equipment reliability, reducing energy consumption, and meeting sustainability targets.
Primary Applications
- High-Density Data Center Cooling (HDDC): The primary application domain. SS-DCT units are integrated into Rear-Door Heat Exchangers (RDHX), In-Row Cooling Units (IRCU), and Containment Systems to manage heat loads ranging from 30 kW to 100+ kW per rack. The dry coil configuration enables Free Cooling (FC) operation during favorable ambient conditions, significantly reducing PUE (Power Usage Effectiveness) values.
- Mixed-Mode Cooling Systems: SS-DCT dry coils operate in conjunction with Chilled Water (CW) coils in hybrid heat exchangers, providing seamless transition between free-cooling and mechanical cooling modes based on ambient conditions and thermal load.
- Telecommunications Data Centers: High-reliability cooling for telecom network infrastructure where 99.999% (five nines) uptime is required. The corrosion-resistant stainless steel construction ensures long service life in varied environmental conditions.
- Edge Computing Facilities: Compact, efficient dry coil solutions for distributed edge data centers with space constraints and limited cooling infrastructure.
- Industrial Process Cooling: Secondary applications in pharmaceutical manufacturing, food processing, and chemical plants where stainless steel construction is required for hygiene and corrosion resistance.
- Renewable Energy Systems: Heat recovery and thermal management in solar thermal systems and wind turbine nacelle cooling.
Performance Advantages in Data Center Applications
| Performance Metric | SS-DCT Performance | Industry Benchmark |
|---|---|---|
| Heat Transfer Coefficient (U-value, air-to-air) | 35–65 W/(m²·K) | 25–50 W/(m²·K) |
| PUE Reduction (free-cooling mode) | 1.05 – 1.15 | 1.20 – 1.40 |
| Free Cooling Hours per Year | Up to 4,500+ hours (climate-dependent) |