Spiral Coil Tube (Coiltube) for Shell-and-Tube Stepped Phase-Change Thermal Energy Storage Units
Product Overview
The Spiral Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 337) is a precision-engineered stainless steel tubing component designed specifically for integration into shell-and-tube stepped phase-change thermal energy storage (Phase Change Material Energy Storage, PCM-ES) units. This product represents a critical heat-transfer interface element within advanced thermal storage systems, enabling efficient conversion between sensible heat and latent heat through the utilization of phase-change materials (Phase Change Materials, PCMs) at multiple discrete temperature levels.
The coil tube architecture facilitates compact, high-surface-area heat exchange geometries within confined cylindrical shell housings. By arranging the coil tubes in a helical or spiral configuration, the design maximizes the ratio of heat transfer surface area to volumetric capacity, thereby enhancing the thermal charging and discharging kinetics of the storage unit. This product is the subject of rigorous academic research documented in the study titled "Research on Heat Storage Characteristics of Spiral Coil Tube Shell-and-Tube Stepped Phase-Change Thermal Energy Storage Units", which provides the theoretical and experimental foundation for its application.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, typically conforming to the following material specifications:
- Primary Alloy Grade: AISI 304 (UNS S30400) or AISI 316L (UNS S31603), selected based on the operating temperature range and corrosive medium compatibility requirements of the specific thermal storage application.
- Corrosion Resistance: Excellent resistance to oxidation and pitting corrosion at elevated temperatures, ensuring long-term structural integrity within the thermal cycling environment of phase-change storage units.
- Thermal Conductivity: Approximately 16.3 W/(m·K) for AISI 304 grade at 20°C, providing adequate thermal transport while maintaining mechanical robustness.
- Thermal Expansion Coefficient: ~17.3 × 10⁻⁶ /K (20–100°C), compatible with the differential thermal expansion of shell materials and PCM encapsulation.
- Mechanical Properties: Tensile strength ≥ 515 MPa, yield strength ≥ 205 MPa (AISI 304 annealed condition), ensuring resistance to thermal fatigue and cyclic stress during repeated charge/discharge operations.
- Maximum Service Temperature: Up to 870°C (AISI 304) or 815°C (AISI 316L), accommodating high-temperature PCM systems.
Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Product Category | Spiral Coil Tube (Coiltube) | — |
| Product Code | 337 | — |
| Outer Diameter (OD) | 6 – 50 | mm |
| Wall Thickness | 0.5 – 3.0 | mm |
| Coil Pitch (Helical Spacing) | 8 – 40 | mm |
| Coil Diameter (Bundling) | 100 – 600 | mm |
| Coil Length | 200 – 3000 | mm |
| Number of Turns | 5 – 200 | turns |
| Material Grade | AISI 304 / 304L / 316L / 321 | — |
| Surface Finish | Mirror polished (Ra ≤ 0.4 μm) / Commercial pickled | — |
| End Connection Type | Flat end / Flanged / Threaded / Welded stub | — |
| Operating Pressure | Up to 1.6 | MPa |
| Operating Temperature Range | -196 to 870 | °C |
| PCM Temperature Stages | Multi-step (e.g., 40°C, 60°C, 80°C, 100°C, 150°C) | — |
| Heat Storage Efficiency | ≥ 85% (charging), ≥ 82% (discharging) | % |
| Design Life | ≥ 20,000 thermal cycles | cycles |
Manufacturing Process
The production of the spiral coil tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, structural integrity, and thermal performance:
- Material Preparation: Cold-rolled or hot-finished stainless steel strip or seamless tubing is procured and subjected to incoming quality inspection including chemical composition analysis (Optical Emission Spectroscopy, OES), mechanical property testing, and ultrasonic flaw detection.
- Tubing Forming: The base tubing is produced via cold drawing or cold rolling processes to achieve precise inner diameter (ID), outer diameter (OD), and wall thickness tolerances within ±0.05 mm.
- Spiral Coiling: The straight tube is helically formed using computer-controlled (Computer Numerical Control, CNC) coiling machinery. The coiling process is executed at controlled temperatures (cold coiling or warm forming at 200–400°C) to prevent work hardening-induced cracking and ensure uniform curvature throughout the helical geometry.
- Stress Relief Annealing: Post-coiling stress relief annealing is performed at 1050°C in a protective atmosphere (nitrogen or vacuum) followed by controlled cooling, eliminating residual stresses introduced during forming and restoring full mechanical properties.
- Heat Treatment & Pickling: The annealed coils undergo acid pickling and passivation treatment to remove scale and oxide layers, restoring the chromium oxide passive film essential for corrosion resistance.
- End Preparation & Assembly: Tube ends are cut, deburred, and prepared for connection (welding, threading, or flanging). Multiple coil tubes are bundled and assembled within the shell-and-tube housing at designated PCM temperature steps.
- Quality Inspection: Final inspection includes dimensional verification (Coordinate Measuring Machine, CMM), hydrostatic pressure testing (1.5× operating pressure, held for 30 minutes), visual examination, and non-destructive testing (Eddy Current Testing, ECT).
Applications
The spiral coil tube is integral to a diverse range of thermal energy management systems:
- Industrial Waste Heat Recovery: Capturing and storing low-grade and medium-grade waste heat from industrial processes (e.g., glass manufacturing, cement kilns, steel rolling mills) for later utilization, improving overall process energy efficiency.
- Solar Thermal Energy Storage: Storing concentrated solar thermal energy in stepped-temperature PCM units to enable dispatchable power generation in Concentrated Solar Power (CSP) plants and industrial solar heating systems.
- Building Heating & Cooling: Integration into district heating networks and commercial building thermal management systems for load shifting and peak shaving, utilizing PCM units at multiple temperature stages (e.g., 40°C, 60°C, 80°C) to match diverse heating demands.
- Process Industry Temperature Control: Application in food processing, pharmaceutical manufacturing, and chemical industry where precise temperature control and thermal buffering are critical for product quality and safety.
- Electric Vehicle Thermal Management: Emerging application in battery thermal management systems and vehicle heating/cooling subsystems, leveraging the compact high-density storage capability of coil tube PCM units.
- Renewable Energy Hybrid Systems: Coupling with wind and solar photovoltaic systems to store excess electrical energy converted to thermal energy, enabling time-shifted energy delivery and grid stabilization.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management and certification framework to ensure product conformity and reliability:
- ISO 9001:2015 — Quality Management Systems certification covering all manufacturing and supply chain operations.
- ISO 14001:2015 — Environmental Management Systems certification demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management Systems certification.
- GB/T 14976 — Chinese National Standard for seamless stainless steel tubes, governing dimensional tolerances and mechanical properties.
- ASTM A269 — American Society for Testing and Materials standard for seamless austenitic stainless steel tubing, applicable for export and international projects.
- EN 10216-5 — European standard for seamless and welded stainless steel tubes for technical purposes.
- Pressure Vessel Compliance: Products designed for pressure-containing applications comply with applicable regulations including GB/T 150 (Chinese Pressure Vessel Code) and ASME Boiler and Pressure Vessel Code (BPVC) Section VIII where required.
Unique Selling Points
Stepped Phase-Change Architecture: The coil tube design enables multi-stage temperature matching within a single shell-and-tube unit, allowing simultaneous storage and retrieval of thermal energy at different temperature levels. This stepped configuration significantly improves the overall utilization efficiency of the thermal storage system compared to single-temperature PCM designs.
Compact High-Density Geometry: The helical coil arrangement achieves a heat transfer surface area density exceeding 500 m²/m³ within the shell volume, enabling compact system footprints suitable for space-constrained industrial and commercial installations.
Academic-Validated Performance: Product performance parameters are derived from rigorous experimental research and validated through computational fluid dynamics (Computational Fluid Dynamics, CFD) modeling, providing quantifiable guarantees on charging rates, discharging rates, and cycle life.
Customizable Configuration: Coil tube dimensions, pitch, turn count, material grade, and end connections are fully customizable to match specific PCM types, shell geometries, and process requirements, offering flexible engineering solutions.
Long-Term Reliability: The austenitic stainless steel construction combined with stress-relief annealing ensures resistance to thermal fatigue over 20,000+ charge/discharge cycles, minimizing maintenance requirements and lifecycle costs.