Double Helix Stainless Steel Coil Tube with Expanded Graphite-Enhanced Phase Change Material (PCM) Heat Storage System
Product Overview
The Double Helix Coil Tube with Expanded Graphite-Enhanced Phase Change Material (PCM) Heat Storage System is an advanced thermal energy storage (TES) component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product integrates a precision-engineered double-helix stainless steel coil tube with expanded graphite (EG) reinforced PCM to achieve superior heat transfer enhancement and thermal storage/release performance. The system is designed to address the inherent low thermal conductivity limitation of conventional phase change materials, enabling efficient latent heat storage and retrieval in a compact volumetric configuration.
The double-helix geometry significantly increases the effective heat transfer surface area per unit volume compared to single-helix or straight-tube designs, while the expanded graphite matrix embedded within the PCM acts as a high-conductivity thermal bridge, reducing thermal resistance at the PCM-coil interface and accelerating the phase transition kinetics.
Material & Properties
Coil Tube Material
- Base Material: Austenitic stainless steel (SS), conforming to ASTM A312 / ASME SA-312 standards
- Typical Grades: 304 (UNS S30400), 304L (UNS S30403), 316 (UNS S31600), 316L (UNS S31603)
- Corrosion Resistance: Excellent resistance to oxidizing environments, acidic media, and high-temperature oxidation up to 870 °C (304) and 925 °C (316)
- Mechanical Properties: Tensile strength ≥ 515 MPa (304), elongation ≥ 40%, yield strength ≥ 205 MPa
- Thermal Conductivity: 16.3 W/(m·K) at 100 °C (304 grade)
- Surface Finish: Electropolished (Ra ≤ 0.4 μm) or passivated interior to minimize fouling and maximize heat transfer efficiency
Expanded Graphite (EG) Component
- Type: Intercalated expanded graphite (natural or synthetic)
- Thermal Conductivity: 100–150 W/(m·K) (in-plane), 2–5 W/(m·K) (through-plane)
- Porosity: 90–95%
- Specific Surface Area: 100–200 m²/g
- Operating Temperature Range: −200 °C to 600 °C
- Chemical Stability: Inert to most organic and inorganic PCM compounds
Phase Change Material (PCM) Compatibility
- Paraffin-based PCMs: Melting points 25–60 °C; thermal conductivity enhancement factor 3–8× with EG addition
- Hydrate-based PCMs: Melting points 5–30 °C; compatible with EG at loadings of 5–15 wt%
- Aluminum Alloy PCMs: Melting points 400–600 °C; suitable for high-temperature industrial applications
Specifications
| Parameter | Specification |
|---|---|
| Product Series | JX-DHCT-346 (Double Helix Coil Tube, Catalog No. 346) |
| Tube Outer Diameter (OD) | 6 mm – 51 mm (customizable) |
| Tube Wall Thickness | 0.5 mm – 3.0 mm |
| Helix Coil Diameter | 50 mm – 500 mm |
| Helix Pitch (Single Turn) | 10 mm – 80 mm |
| Number of Helical Turns | 2 – 100 (per helix leg) |
| Double Helix Configuration | Two offset helical legs wound on common axis (180° phase offset) |
| Coil Length (Total) | 0.5 m – 10 m (configurable) |
| Operating Temperature Range | −50 °C to 400 °C (standard); up to 600 °C (special grade) |
| Maximum Operating Pressure | 1.6 MPa (standard); 4.0 MPa (heavy-wall) |
| Heat Transfer Enhancement Factor | 2.5× – 6.0× vs. single-helix baseline |
| Charging Time Reduction | 40% – 65% vs. conventional single-tube PCM modules |
| Discharging Efficiency | ≥ 92% (latent heat recovery rate) |
| Cyclic Stability | ≥ 10,000 charge/discharge cycles with < 5% capacity degradation |
| Connection Type | Flanged, threaded (NPT/BSP), or welded (butt/socket) |
| Surface Treatment | Passivation, electropolishing, or PTFE coating (optional) |
| Applicable Standards | ASTM A312, ASME SA-312, EN 10216-5, GB/T 14976 |
Manufacturing Process
- Material Selection & Inspection: Cold-rolled stainless steel strip or seamless tube stock is procured and subjected to spectroscopic analysis (OES), hardness testing, and visual inspection to verify grade conformance.
- Pipe Forming & Welding: For welded tube, precision roll-forming is followed by automatic Argon arc welding (TIG/IGAW) with 100% helium or dye penetrant testing of weld seams. For seamless tube, hot- or cold-drawn pipe is used directly.
- Double Helix Coiling: The formed tube is coiled using CNC-controlled helical coiling equipment. Two helical legs are wound simultaneously with a precise 180° angular offset to form the double-helix geometry. Coiling parameters (diameter, pitch, tension) are controlled to maintain uniform geometry and prevent tube deformation or ovality exceeding 2%.
- Heat Treatment & Stress Relief: Post-coiling solution annealing (1050 °C for 304/316, water quench) or stress-relief annealing (850–900 °C, air cool) is performed to eliminate residual stresses from forming and coiling operations.
- Surface Finishing: Interior surfaces are electropolished or passivated to reduce roughness and improve corrosion resistance. Exterior surfaces may receive bead blasting or passivation treatment.
- Expanded Graphite Integration: Expanded graphite flakes or sheets are incorporated into the PCM matrix through mechanical mixing or vacuum impregnation. The EG-PCM composite is then loaded into the annular space surrounding the double-helix coil tube within a containment vessel.
- Assembly & Sealing: The coil tube assembly is inserted into the PCM-EG container. End caps, flanges, or threaded fittings are installed and sealed using high-temperature gaskets (graphite, PTFE, or metallic spiral wound).
- Pressure Testing & Quality Assurance: Each unit undergoes hydrostatic pressure testing at 1.5× the maximum operating pressure for a minimum hold time of 30 minutes. Non-destructive testing (NDT) includes eddy current inspection of tube walls and ultrasonic testing of welds.
- Performance Validation: Thermal cycling tests are conducted to verify charging/discharging rates, heat transfer enhancement factors, and long-term cyclic stability under simulated operating conditions.
Applications
Industrial Thermal Energy Storage
- Waste heat recovery systems in steel, glass, and cement manufacturing
- Industrial process heating and cooling load leveling
- Steam generation and thermal buffer systems
Building Energy Systems
- Solar thermal energy storage for space heating and domestic hot water (DHW)
- Peak-shaving and demand-response thermal storage in commercial HVAC systems
- Ground-coupled heat pump thermal enhancement
Electronics & Power Systems
- Thermal management for lithium-ion battery packs (temperature equalization)
- Power electronics cooling and thermal buffering
- Concentrated solar power (CSP) thermal storage units
Transportation
- Electric vehicle (EV) battery thermal management systems
- Regenerative braking energy thermal storage
- Marine and aerospace thermal regulation
Medical & Laboratory
- Cryogenic sample storage and temperature-controlled incubation
- Medical device thermal management
Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- ASME BPV Code — Pressure Vessel Code Section VIII compliance (where applicable)
- EN 10204 3.1 — Third-party material certification (mill test certificates)
- CE Marking — Conformity with European Pressure Equipment Directive (PED 2014/68/EU)
- NACE MR0175 / ISO 15156 — Compliance for sour service environments (H₂S-containing media)
- ASTM/ASME Material Certifications — Full traceability from raw material to finished product
- Internal NDT Protocols — 100% coverage: radiographic testing (RT), ultrasonic testing (UT), dye penetrant testing (PT), and eddy current testing (ET)
Unique Selling Points
1. Double-Helix Geometry Advantage: The dual-offset helical coil design nearly doubles the heat transfer surface area per unit volume compared to single-helix configurations, while promoting secondary flow and turbulence enhancement within the PCM, resulting in a 2.5–6.0× improvement in heat transfer coefficient.
2. Expanded Graphite Thermal Network: The incorporation of expanded graphite creates a percolating high-conductivity pathway throughout the PCM volume, dramatically reducing the radial thermal resistance gradient and eliminating the "cold spot" problem inherent in conventional PCM modules.
3. Accelerated Phase Transition Kinetics: Combined EG and double-helix geometry reduces PCM charging time by 40–65%, enabling rapid thermal response suitable for dynamic load environments.
4. Superior Cyclic Durability: Validated performance over 10,000+ charge/discharge cycles with less than 5% capacity degradation, ensuring long service life and low total cost of ownership (TCO).
5. Scalable & Customizable Design: Modular construction allows customization of coil diameter, pitch, tube dimensions, and PCM type to match specific thermal load profiles and installation constraints.
6. Corrosion-Resistant Construction: Full austenitic stainless steel construction ensures compatibility with aggressive PCM compounds (acids, hydrates, molten salts) and extends service life in corrosive environments.
Technical Summary
The JX-DHCT-346 Double Helix Coil Tube with Expanded Graphite-Enhanced PCM represents a state-of-the-art solution for compact, high-performance latent heat thermal energy storage. By synergistically combining the geometric heat transfer enhancement of the double-helix stainless steel coil with the conductive network of expanded graphite within the PCM matrix, this product achieves thermal storage densities and charging/discharging rates that significantly outperform conventional single-tube PCM systems. It is particularly suited for applications requiring rapid thermal response, high energy density, and long-term reliability in industrial, building, and transportation sectors.