Stainless Steel Spiral Coil Tube — Model JSX-CT Series
Product Overview
The Stainless Steel Spiral Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered helical tube product designed for advanced thermal management applications. This coil tube series is specifically developed for integration into closed-loop ground source heat pump (GSHP) systems and other high-efficiency heat exchange environments where superior thermal conductivity, flow resistance performance, and long-term mechanical integrity are paramount.
Informed by extensive research on the heat transfer and flow resistance characteristics of spiral coil heat exchangers — particularly those employing polymer composite materials in closed-loop geothermal applications — the JSX-CT Series leverages the proven advantages of helical geometry to maximize heat exchange surface area while minimizing pressure drop and fluid friction losses. The coil tube design exploits the secondary flow (Dean vortices) generated within the helical channel, which significantly enhances turbulent mixing and convective heat transfer coefficients compared to conventional straight-tube configurations.
Material & Properties
Base Material
The JSX-CT Series coil tubes are fabricated from high-grade austenitic stainless steel, primarily AISI 304 (UNS S30400) and AISI 316L (UNS S31603), selected for their exceptional corrosion resistance, mechanical strength, and compatibility with a wide range of working fluids including water, brine solutions, and geothermal fluids.
Key Material Properties
- Chemical Composition (AISI 304): Carbon ≤0.08%, Chromium 18.0–20.0%, Nickel 8.0–10.5%, Manganese ≤2.0%, Silicon ≤1.0%
- Chemical Composition (AISI 316L): Carbon ≤0.03%, Chromium 16.0–18.0%, Nickel 10.0–14.0%, Molybdenum 2.0–3.0%
- Tensile Strength: ≥520 MPa (AISI 304); ≥480 MPa (AISI 316L)
- Yield Strength: ≥205 MPa
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (AISI 304)
- Operating Temperature Range: −196°C to +870°C
- Corrosion Resistance: Excellent resistance to pitting, crevice, and intergranular corrosion; particularly suited for chloride-containing geothermal environments
- Surface Finish: 2B, BA (Bright Annealed), or No.4 hairline finish; Ra ≤ 0.8 μm available upon request
Performance Characteristics in Spiral Configuration
Research on heat transfer and flow resistance in spiral coil heat exchangers demonstrates that the helical geometry of the JSX-CT Series provides the following performance advantages:
- Enhanced Nusselt Number (Nu): The Dean number (De) effect in helical tubes increases the average Nusselt number by 30–60% compared to equivalent straight tubes at the same Reynolds number, resulting in substantially improved heat transfer efficiency.
- Optimized Flow Resistance: While the friction factor (f) in helical tubes is higher than in straight tubes, the overall pressure drop per unit heat transferred is favorable, yielding an improved heat transfer-to-pressure-drop ratio.
- Compact Heat Exchange Area: The spiral coil configuration achieves a volumetric heat transfer coefficient up to 3–5 times that of shell-and-tube heat exchangers of equivalent footprint.
- Self-Cleaning Effect: The secondary Dean flow promotes continuous surface renewal, reducing fouling tendencies in geothermal brine applications.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Spiral Coil Tube (Coiltube) | — |
| Model Series | JSX-CT Series | — |
| Material Grade | AISI 304 / AISI 316L / 2205 Duplex (upon request) | ASTM A213 / ASTM A269 |
| Outer Diameter (OD) | 3.175 mm – 32.00 mm (1/8" – 1/2") | ASTM B513 / DIN 17475 |
| Wall Thickness | 0.30 mm – 2.00 mm | — |
| Coil Pitch (Helix Pitch) | 10 mm – 150 mm (configurable) | — |
| Coil Mean Diameter | 50 mm – 1,000 mm | — |
| Coil Length (Total Developed Length) | 1 m – 500 m per coil assembly | — |
| End Form | Plain end, flared, threaded, or customized | ASME B1.20.1 |
| Surface Treatment | 2B / BA / No.4 / Electropolished | ASTM A967 |
| Maximum Working Pressure | Up to 4.0 MPa (subject to OD and wall thickness) | ASME B31.3 |
| Design Temperature | −40°C to +250°C (standard); up to +400°C (special order) | — |
| Delivery Form | Coiled on spool / Bundled with end caps | — |
| Compliance Standards | ASTM, EN, DIN, GB, ASME | — |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. | — |
| Product Catalog No. | 858 | — |
Manufacturing Process
1. Raw Material Selection and Inspection
Only certified stainless steel strip or seamless tube stock from accredited mills (e.g., Outokumpu, Voestalpine, Tsingshan, or equivalent) is accepted. Each batch undergoes incoming inspection for chemical composition (via Optical Emission Spectrometry — OES), mechanical properties, and surface quality per ASTM A213 / ASTM A269 requirements.
2. Cold Forming / Coil Winding
Stainless steel tube is cold-formed into a precise helical coil using CNC-controlled coiling equipment. The forming parameters — including coil pitch, mean diameter, and winding tension — are optimized to prevent cross-sectional distortion, minimize residual stress, and ensure geometric uniformity. The helical angle (α) is calculated to achieve the desired Dean number for optimal heat transfer performance in the target application.
3. Heat Treatment (if required)
For applications requiring stress relief or enhanced corrosion resistance, the formed coil undergoes solution annealing at 1050–1150°C followed by rapid water quenching, per ASTM A967. This process restores full austenitic microstructure and eliminates cold-work hardening effects.
4. Surface Finishing
The coil tube may undergo additional surface finishing including:
- Bright Annealing (BA): Annealing in a controlled reducing atmosphere (H₂/N₂) to achieve a smooth, reflective surface with Ra ≤ 0.4 μm.
- Electropolishing: Electrochemical dissolution to achieve Ra ≤ 0.2 μm, removing surface contaminants and enhancing passive film formation.
- Passivation: Nitric acid or citric acid passivation per ASTM A967 to maximize corrosion resistance.
5. End Processing
Tube ends are cut to precise lengths using laser or abrasive cutting, followed by deburring, chamfering, or end-forming (threading, flaring, crimping) as specified by the customer's integration requirements.
6. Quality Inspection and Testing
Each coil tube assembly undergoes comprehensive quality assurance including:
- Dimensional verification (OD, wall thickness, coil pitch, mean diameter) using laser micrometers and CMM inspection
- Hydrostatic pressure testing at 1.5× working pressure for 30 seconds minimum
- Visual and eddy current inspection for surface defects and wall thickness uniformity
- Corrosion testing (salt spray test per ASTM B117, minimum 1,000 hours without red rust for 316L grade)
7. Packaging and Dispatch
Finished coil tubes are wound onto protective spools with anti-corrosion wrapping (VCI paper or PE film) and secured with steel strapping. Each package is labeled with product identification, material certification, and traceability data.
Applications
Primary Application: Closed-Loop Ground Source Heat Pump Systems
The JSX-CT Series coil tubes are specifically engineered for closed-loop ground source heat pump (GSHP) systems, where they serve as the primary heat exchange element in the following configurations:
- Horizontal Ground Loop Systems: Spiral coil tubes installed in horizontal boreholes or trenches for geothermal heat extraction/ground cooling in residential and commercial buildings.
- Vertical Ground Loop Systems: U-tube and spiral coil configurations for deep borehole heat exchangers.
- Hybrid Polymer-Steel Coil Assemblies: Integration with polymer (PE-RT, PEX) spiral coil heat exchangers for optimized thermal-hydraulic performance, as studied in advanced heat transfer research.
Additional Applications
- Industrial Process Heating and Cooling: Spiral coil heat exchangers for chemical processing, food and beverage pasteurization, and pharmaceutical applications.
- Solar Thermal Systems: Coil tubes for direct-expansion solar air heaters and solar water heaters.
- Refrigeration and HVAC: Evaporator and condenser coils for commercial refrigeration units and heat recovery systems.
- Automotive and Marine: Intercooler coils, fuel cooler assemblies, and marine heat exchangers.
- Biomedical Equipment: Precision temperature control coils for laboratory and medical devices.
- Power Generation: Coil tubes for waste heat recovery systems and geothermal power plant heat exchangers.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications and standards compliance:
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health and Safety Management Systems
- EN 10204 3.1 — Material Test Reports (Mill Certificate)
- CE Marking — Conformity with European directives
- PED 2014/68/EU — Pressure Equipment Directive compliance (where applicable)
- ASME Stamp — For pressure-containing coil assemblies (upon request)
- NADCAP — National Aerospace and Defense Contractors Accreditation Program (special order)
- Material Compliance: ASTM A213, ASTM A269, ASTM A312, EN 10216-5, EN 10217-7, DIN 17475, GB/T 12771, GB/T 13296
Unique Selling Points
- Research-Validated Thermal Performance: The JSX-CT Series design is informed by published academic research on the heat transfer and flow resistance characteristics of spiral coil heat exchangers in closed-loop GSHP systems. This ensures that coil geometry parameters (pitch, mean diameter, helix angle) are optimized for maximum heat transfer efficiency with minimal pressure drop.
- Dean Vortex Enhancement: The helical coil geometry inherently generates Dean vortices that enhance turbulent mixing, resulting in 30–60% higher Nusselt numbers compared to equivalent straight-tube configurations — translating to significantly more compact heat exchange systems.
- Premium Material Selection: Available in AISI 304, AISI 316L, and 2205 Duplex stainless steel grades, providing exceptional resistance to geothermal brine corrosion, chloride pitting, and long-term thermal cycling fatigue.
- Full Customization Capability: Coil pitch, mean diameter, total developed length, end forms, and surface finishes are fully customizable to match specific system integration requirements and thermal-hydraulic design targets.
- End-to-End Traceability: Each coil tube assembly is traceable from raw material mill certification through manufacturing, inspection, and dispatch, with full EN 10204 3.1 material test reports provided.
- Compact Volumetric Efficiency: The spiral coil configuration achieves up to 3–5× the volumetric heat transfer coefficient of conventional shell-and-tube heat exchangers, enabling space-saving installations in ground loop systems.