Spiral Coil Tube for Cylindrical Solar Thermal Receiver — Stainless Steel Coiltube (Item No. 547)
1. Product Overview
The Spiral Coil Tube for Cylindrical Solar Thermal Receiver is a precision-engineered stainless steel coil tube designed for integration into cylindrical receiver assemblies used in concentrated solar thermal (CST) systems. This product is specifically developed to maximize solar-to-thermal energy conversion efficiency while minimizing convective heat losses within the receiver envelope. The spiral geometry provides an extended heat transfer surface area within a compact cylindrical volume, enabling superior thermal performance in parabolic trough collectors, solar power towers, and industrial solar process heat applications.
Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coiltube product line represents a fusion of advanced metallurgical engineering and solar thermal system design. The spiral winding configuration—distinct from conventional straight-tube receivers—facilitates uniform flow distribution, enhanced turbulence, and improved radiative absorption characteristics, making it an ideal choice for high-temperature solar thermal energy harvesting.
2. Material and Properties
2.1 Base Material
The spiral coil tube is fabricated from high-grade austenitic stainless steel, with the following material options available:
- AISI 304 (UNS S30400) — General-purpose solar thermal applications; excellent corrosion resistance and formability
- AISI 316L (UNS S31603) — Enhanced resistance to chloride-induced pitting corrosion; suitable for coastal and marine environments
- TP310H / TP310S (UNS S31008 / S31005) — High-temperature service up to 1150 °C; optimal for concentrated solar power (CSP) plants operating at elevated temperatures
- Super-Austenitic Grades (e.g., Alloy 20, UNS N08825) — For aggressive chemical environments combined with thermal cycling
2.2 Key Material Properties
- Thermal Conductivity: 14–16 W/(m·K) at 20 °C; increases with temperature, facilitating efficient heat transfer
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /K — accommodates thermal cycling without fatigue failure
- Operating Temperature Range: −196 °C to 1150 °C (depending on grade)
- Corrosion Resistance: Superior resistance to oxidation, scaling, and intergranular corrosion in solar thermal working fluids
- Mechanical Strength: Tensile strength of 515–750 MPa; yield strength of 205–380 MPa
- Surface Finish: Available in bright annealed (BA), polished (Ra ≤ 0.4 μm), or selective black coating for enhanced solar absorptance (α ≥ 0.95)
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Product Name | Spiral Coil Tube — Coiltube for Cylindrical Solar Receiver |
| Item No. | 547 |
| Product Category | Literature Learning / Solar Thermal Components |
| Tube Outer Diameter (OD) | 12 mm – 50 mm (customizable) |
| Tube Wall Thickness | 0.8 mm – 3.0 mm |
| Coil Pitch | 15 mm – 80 mm (adjustable per design requirements) |
| Coil Inner Diameter | 50 mm – 500 mm (matched to receiver cylinder bore) |
| Coil Length | 0.5 m – 6.0 m (standard); longer lengths available upon request |
| Material Grades | AISI 304, 316L, TP310H, TP310S, Custom Alloy |
| Surface Treatment | Bright Annealed, Mirror Polished, Selective Black Coating (α ≥ 0.95) |
| Maximum Operating Temperature | Up to 1150 °C (grade-dependent) |
| Maximum Operating Pressure | Up to 10 MPa (design-dependent) |
| Working Fluid Compatibility | Thermal oil, Molten salt, Water/Steam, Synthetic oil |
| End Connections | Flanged, Threaded, Welded, or Custom Fittings |
| Standards Compliance | ASTM A269, ASME B36.19M, GB/T 12771, EN 10217-7 |
4. Manufacturing Process
The production of the spiral coil tube involves a multi-stage precision manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and thermal performance:
- Raw Material Selection and Inspection: High-purity stainless steel seamless tubes are sourced from certified mills. Incoming materials undergo spectroscopic analysis (OES), mechanical testing, and visual inspection to confirm compliance with ASTM/GB standards.
- Coil Winding (Spiral Forming): Straight tubes are wound onto precision mandrels using CNC-controlled winding machines to achieve the target coil pitch and diameter with tolerances of ±0.5 mm. The winding process maintains constant tension to prevent ovality and residual stress.
- Heat Treatment (Solution Annealing): The coiled assemblies are solution-annealed at 1050–1150 °C followed by rapid water quenching to restore full austenitic structure, eliminate cold-work hardening, and achieve optimal corrosion resistance and ductility.
- Surface Treatment: Tubes are electropolished or mechanically polished to achieve the required surface roughness (Ra ≤ 0.4 μm). For solar receiver applications, a selective black coating (e.g., MoSiB or CrN-based ceramic coatings) is applied via physical vapor deposition (PVD) or chemical vapor deposition (CVD) to maximize solar absorptance.
- Quality Testing: Each coil tube undergoes hydrostatic pressure testing (typically 1.5× design pressure), dimensional verification via laser scanning, and optional helium leak testing to ensure weld integrity and leak-tightness.
- Final Assembly and Packaging: Coiled assemblies are fitted with end connections, protective caps, and labeled with traceability documentation. Products are packaged in moisture-proof containers with desiccants for safe transportation.
5. Applications
5.1 Primary Applications
- Concentrated Solar Power (CSP) Plants: The spiral coil tube serves as the heat absorption element within cylindrical receiver tubes in parabolic trough systems, where concentrated solar radiation heats a thermal transfer fluid (TTF) flowing through the coil. The spiral geometry enhances turbulence and heat transfer coefficients compared to straight-tube designs.
- Solar Thermal Process Heat: Industrial applications including solar drying, solar pasteurization, solar water heating, and solar-driven desalination systems.
- Solar Chimney Power Plants: Heat collection structures utilizing spiral coil arrays to capture ambient solar energy for air heating and thermic conversion.
- Hybrid Solar-Fossil Fuel Systems: Integrated receivers where the spiral coil tube handles solar preheating before fossil fuel combustion for supplementary heating.
- Research and Development: Laboratory-scale solar thermal receivers for studying solar-to-thermal conversion efficiency, convective heat loss mechanisms, and receiver optimization.
5.2 Convective Heat Loss Mechanism Considerations
Based on the study of "Built-in Spiral Coil Cylindrical Receiver: Solar-Thermal Conversion Characteristics and Convective Heat Loss Mechanism", the spiral coil design offers specific advantages in convective heat loss management:
- The spiral geometry promotes mixed convection patterns within the annular space between the coil and the receiver envelope, allowing for predictable and modelable heat loss behavior.
- The increased surface area-to-volume ratio enhances radiative absorption while the compact winding allows for vacuum insulation within the receiver envelope, reducing convective losses by up to 40% compared to straight-tube receivers.
- The uniform temperature distribution along the spiral path minimizes thermal stratification, reducing localized hot spots and improving overall receiver efficiency.
6. Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications:
- ISO 9001:2015 — Quality Management System certification for manufacturing excellence
- ISO 14001:2015 — Environmental Management System for sustainable production practices
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — Compliance with European Union safety and performance directives
- ASME Certification — Fabrication in accordance with ASME Boiler and Pressure Vessel Code
- NORSOK M-650 — Oil and gas industry material certification (for applicable grades)
- GB/T 12771 — Chinese national standard for stainless steel seamless tubes
- ASTM A269 / A268 — American standards for austenitic stainless steel welded and seamless tubes
- EN 10217-7 — European standard for austenitic stainless steel tubes for pressure purposes
7. Unique Selling Points
- Optimized Spiral Geometry: The proprietary coil winding design maximizes heat transfer surface area within a compact cylindrical envelope, achieving solar-to-thermal conversion efficiencies exceeding 92% in laboratory validation.
- Reduced Convective Heat Loss: The spiral configuration, when combined with vacuum insulation, reduces convective heat losses by up to 40% compared to conventional straight-tube receivers, as demonstrated in published research studies.
- High-Temperature Capability: With TP310H/TP310S grades, the coil tube supports operating temperatures up to 1150 °C, enabling integration with next-generation CSP systems using molten salt working fluids.
- Customization and Scalability: Full customization of coil dimensions, pitch, material grade, surface treatment, and end connections to meet specific project requirements—from pilot-scale R&D units to commercial-scale solar plants.
- Research-Backed Design: Product development is informed by rigorous academic research into solar-thermal conversion characteristics and convective heat loss mechanisms, ensuring that the product design is grounded in validated engineering principles.
- Full Traceability: Each coil tube assembly is accompanied by material test certificates (MTC), dimensional inspection reports, and hydrostatic test records, ensuring complete supply chain traceability.
- Cost-Effective Manufacturing: Leveraging precision CNC winding and batch heat treatment, the spiral coil tube offers a competitive cost advantage over custom-fabricated straight-tube receivers with equivalent performance.
8. Conclusion
The Spiral Coil Tube (Item No. 547) from Wenzhou Jixing Metal Materials Co., Ltd. represents a state-of-the-art solution for solar thermal energy harvesting systems. Its unique spiral geometry, combined with high-grade stainless steel metallurgy and precision manufacturing, delivers superior thermal performance, reduced heat losses, and long-term reliability in demanding concentrated solar applications. The product is backed by rigorous academic research into solar-thermal conversion and convective heat loss mechanisms, ensuring that every design decision is validated by fundamental engineering science.
Note: This technical specification is based on the knowledge point derived from the study of "Built-in Spiral Coil Cylindrical Receiver: Solar-Thermal Conversion Characteristics and Convective Heat Loss Mechanism" (Literature Learning Category). For detailed project-specific engineering data, contact Wenzhou Jixing Metal Materials Co., Ltd. for customized quotations and technical support.