Stainless Steel Coil Tube for Thermal Energy Storage Systems
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product Reference No.: 881 | Category: Coil Tube (Coiltube) for Ice Accumulation & Discharge Systems
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered continuous helical tube product designed for integration into ice storage heat exchangers (盘管式冰蓄冷器) and thermal energy storage systems. These coil tubes serve as the primary heat transfer medium within ice-on-coil (IOC) and ice-in-coil (IIC) systems, facilitating efficient freezing and melting (discharge/release) cycles of ice slurry or solid ice layers formed on the tube surface.
Based on experimental research into the discharge process of coil-type ice accumulators (《盘管式冰蓄冷器释冷过程实验研究》), these coil tubes are specifically optimized to maximize heat transfer efficiency during both the charging (freezing) and discharging (melting/release) phases. The helical geometry promotes turbulent flow characteristics within the tube, enhancing convective heat transfer coefficients and ensuring uniform ice layer formation and controlled release.
2. Material & Properties
The coil tubes are manufactured from high-grade austenitic stainless steel, selected for superior corrosion resistance, thermal conductivity, and mechanical integrity under repeated thermal cycling conditions.
- Primary Material Grades: AISI 304 (UNS S30400), AISI 316L (UNS S31603), and 321 (UNS S32100)
- Corrosion Resistance: Excellent resistance to chloride-induced pitting (particularly 316L grade) and oxidation at elevated temperatures (321 grade)
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, ensuring efficient heat exchange between the refrigerant fluid and ice medium
- Operating Temperature Range: -196°C to +870°C, accommodating cryogenic refrigerant conditions and thermal cycling
- Mechanical Strength: Yield strength ≥ 205 MPa (304 grade); tensile strength ≥ 515 MPa
- Surface Finish: Electropolished or passivated interior (Ra ≤ 0.4 μm) to minimize fouling and reduce flow resistance
- Hygienic Compliance: Food-grade surface finish available for potable water and food processing applications
3. Technical Specifications
| Parameter | Specification / Range |
|---|---|
| Tube Outer Diameter (OD) | 12 mm – 38 mm (customizable) |
| Tube Wall Thickness | 0.8 mm – 3.0 mm |
| Coil Pitch (Helix Spacing) | 15 mm – 60 mm (configurable per system design) |
| Coil Diameter | 200 mm – 1,200 mm |
| Tube Length per Coil | 5 m – 150 m (continuous) |
| Material Grade | 304 / 304L / 316 / 316L / 321 / 904L |
| End Connection Type | Plain end, threaded (NPT/BSP), flanged, or brazed |
| Surface Treatment | Passivated, electropolished, or sanitary grade |
| Maximum Operating Pressure | 1.6 MPa – 4.0 MPa (depending on wall thickness) |
| Design Standard | GB/T 12771, ASTM A269, EN 10216-5, JIS G3459 |
| Heat Transfer Enhancement | Up to 2.5× improvement over straight-tube equivalent (due to helical geometry) |
| Thermal Cycling Endurance | > 50,000 freeze-thaw cycles without material degradation |
4. Manufacturing Process
The production of these coil tubes follows a rigorous multi-stage manufacturing sequence to ensure dimensional accuracy, mechanical integrity, and surface quality:
- Raw Material Selection & Inspection: Certified stainless steel seamless or welded tube stock is procured with full mill test certificates (MTC) per EN 10204 3.1/3.2. Incoming inspection includes chemical composition analysis, mechanical property verification, and visual surface examination.
- Tube Straightening & Preparation: Tubes are straightened using cold-drawing or rotary straightening equipment to achieve straightness tolerance within 1 mm/m. Ends are deburred and chamfered for subsequent processing.
- Coiling / Helical Forming: Precision CNC coiling machines form the tube into the required helical geometry with controlled pitch, coil diameter, and uniform bending radius. The forming process maintains wall thickness uniformity within ±10% of nominal value at bend apex.
- Heat Treatment (if applicable): Post-forming annealing at 1050–1100°C with controlled cooling (for 321 grade stabilization) to relieve residual stresses and restore full austenitic microstructure.
- Surface Finishing: Interior and exterior surfaces undergo passivation treatment (citric or nitric acid) or electropolishing to achieve the specified surface roughness and remove any metallic contaminants.
- Quality Control & Testing: Dimensional inspection (OD, wall thickness, pitch accuracy), pressure testing (hydrostatic at 1.5× working pressure), leak testing (helium or nitrogen), and visual inspection per applicable standards.
- Protective Coating & Packaging: Tubes receive protective end caps, desiccant packaging, and are bundled with documentation for shipment.
5. Applications
These stainless steel coil tubes are engineered for demanding thermal management applications, with particular expertise in ice storage systems:
- Ice Storage Heat Exchangers (冰蓄冷器): Primary application — coil-type ice accumulators for peak-load shifting in commercial and industrial HVAC systems, enabling off-peak refrigeration production and on-peak discharge/release
- Thermal Energy Storage Systems: Sensible and latent heat storage for solar thermal, waste heat recovery, and process integration
- Industrial Process Cooling: Cryogenic cooling, pharmaceutical cold storage, and food freezing applications requiring rapid and uniform heat extraction
- Heat Exchanger Cores: Integration into plate-and-tube, shell-and-coil, and double-pipe heat exchanger configurations
- Chemical Processing: Corrosive fluid handling in reactors, condensers, and evaporators where 316L/904L grades are required
- Food & Beverage Industry: Sanitary-grade heat transfer in pasteurization, brewing, and dairy processing equipment
- Power Generation: Condenser cooling coils and thermal energy storage for peak shaving in combined heat and power (CHP) systems
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and product certification systems:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing and quality assurance processes
- ISO 14001:2015 — Environmental Management System for sustainable production practices
- ISO 45001:2018 — Occupational Health and Safety Management
- EN 10204 3.1/3.2 — Inspection certificates for material traceability and compliance verification
- Pressure Vessel & Heat Exchanger Compliance: Products designed and tested per ASME, PED (European Pressure Equipment Directive 2014/68/EU), and TSG standards
- Material Traceability: Full heat number traceability from mill to finished product with accompanying chemical analysis and mechanical test reports
- Non-Destructive Testing (NDT): Available upon request — radiographic testing (RT), ultrasonic testing (UT), and magnetic particle inspection (MT) for weld integrity verification
7. Unique Selling Points
Optimized for Ice Storage Discharge Efficiency: Leveraging experimental research data on coil-type ice accumulator discharge processes, the helical geometry and pitch configuration are specifically tuned to promote uniform ice layer melting, minimize thermal stratification, and achieve discharge efficiency exceeding 85% of theoretical maximum.
- Enhanced Heat Transfer Performance: The helical coil geometry induces Dean vortices within the tube, increasing the Nusselt number (Nu) by up to 2.5× compared to equivalent straight tubes at the same Reynolds number, directly improving both freezing and ice-release rates.
- Superior Thermal Cycling Durability: Austenitic stainless steel retains full mechanical properties through repeated freeze-thaw cycles, eliminating concerns of thermal fatigue cracking common in carbon steel alternatives.
- Customizable Geometry: Coil pitch, diameter, and tube dimensions are fully configurable to match specific thermal load requirements and system design constraints, enabling optimization of ice storage capacity and discharge rate.
- Corrosion-Free Longevity: Inherent resistance to chloride pitting and general corrosion ensures service life exceeding 25 years even in aggressive thermal cycling environments with glycol-based refrigerants.
- Compact Space Utilization: The coiled configuration achieves 60–70% higher heat transfer surface area per unit volume compared to straight-tube alternatives, reducing system footprint in space-constrained installations.
8. Technical Advisory
For optimal system performance in ice storage applications, the following design parameters should be considered when selecting coil tube specifications:
- Coil Pitch Selection: A pitch-to-OD ratio of 2.0–3.5 is recommended to balance flow resistance against heat transfer enhancement. Tighter pitches improve heat exchange but increase pressure drop.
- Refrigerant Flow Velocity: Maintain internal flow velocity between 1.0–2.5 m/s to ensure turbulent flow (Re > 2,300) and prevent ice bridging within the tube bore.
- Wall Thickness Selection: For discharge-intensive systems, thicker walls (≥ 1.5 mm) provide greater thermal mass and structural rigidity to resist ice expansion forces during the freezing phase.
- System Integration: Coil tube configurations should be coordinated with tank geometry, inlet/outlet placement, and flow distribution headers to ensure uniform heat transfer across all coil passes.