Stainless Steel Coil Tube (Coiltube) — Thermal Performance Specification
Product Overview
The Stainless Steel Coil Tube (Coiltube), designated under product series No. 1320 by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered continuous-wound stainless steel tube designed for applications requiring superior thermal conductivity management, particularly in refrigeration and cryogenic systems. This product line has been extensively studied in the context of thermal resistance (Thermal Resistance, $R_{th}$) behavior under varying ice accretion conditions, making it a critical component in ice-based cooling technologies, including ordinary ice ball systems and core ice ball assemblies.
Unlike straight-pipe geometries, the coil tube's helical winding configuration provides a dramatically increased surface-area-to-volume ratio, which enhances heat transfer efficiency while simultaneously introducing complex thermal resistance profiles that vary with ice thickness accumulation on the coil surface.
Material & Properties
Material Composition
- Base Alloy: Austenitic stainless steel grades including 304 (UNS S30400), 316 (UNS S31600), and 316L (UNS S31603)
- Chromium (Cr): 18.0–22.0 wt% — provides corrosion resistance and passivation layer formation
- Nickel (Ni): 8.0–12.0 wt% — stabilizes austenitic microstructure
- Molybdenum (Mo): 2.0–3.0 wt% (316 grades) — enhances pitting and crevice corrosion resistance
- Carbon (C): ≤ 0.03 wt% (L grades) — minimizes intergranular carbide precipitation
Mechanical & Thermal Properties
- Tensile Strength: 515–720 MPa (varies by grade and heat treatment)
- Yield Strength: 205–310 MPa
- Elongation: 35–60% (at break)
- Thermal Conductivity: 14.5–16.5 W/(m·K) at 25°C
- Specific Heat Capacity: 500 J/(kg·K)
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /°C
- Operating Temperature Range: −196°C to +870°C
Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Outer Diameter (OD) | 6.0 – 50.8 | mm |
| Wall Thickness | 0.5 – 3.0 | mm | Coil Diameter | 50 – 500 | mm |
| Coil Length | 1 – 100 | m | Winding Pitch | 1.0 – 5.0 | mm | Surface Finish | Ra 0.4 – 1.6 (polished); Ra 1.6 – 3.2 (pickled) | μm | Ice Accretion Thickness Studied | 0 – 20 | mm | Thermal Resistance Range (with ice) | 0.002 – 0.085 | °C·m²/W | Tolerance on OD | ±0.05 | mm | Tolerance on Wall Thickness | ±10% | — |
Manufacturing Process
- Blank Preparation: Cold-rolled stainless steel strip is inspected for dimensional accuracy and surface quality, with strict control on Cr, Ni, and Mo content per ASTM A213/A269 standards.
- Forming & Welding: The strip is cold-formed into a tubular shape and seam-welded using TIG (Tungsten Inert Gas) or orbital welding techniques to ensure full-penetration welds with minimal distortion.
- Coil Winding: The formed tube is helically wound onto a precision mandrel to achieve the target coil diameter and pitch, maintaining consistent inter-pass spacing to prevent thermal bridging.
- Pickling & Passivation: The coil tube undergoes chemical pickling (typically nitric acid/hydrofluoric acid blend) followed by passivation to remove weld scale and establish a protective chromium oxide film.
- Quality Inspection: Dimensional verification via laser measurement, ultrasonic wall thickness testing, and hydrostatic pressure testing (typically 2× working pressure for 10 seconds).
- Thermal Performance Validation: Each batch undergoes thermal resistance characterization under controlled ice accretion conditions to verify conformance with specified $R_{th}$ values across the operating ice thickness range.
Applications
- Industrial Refrigeration: Coil tubes serve as heat exchange elements in evaporator assemblies where controlled ice formation is utilized for thermal energy storage.
- Cryogenic Systems: Suitable for liquefied natural gas (LNG) handling and low-temperature process cooling where austenitic stainless steel's ductility at cryogenic temperatures is essential.
- Food & Beverage Cooling: Ice ball cooling systems (ordinary and core-type) for beverage dispensing and food preservation, where the coil tube's thermal resistance profile directly impacts cooling efficiency.
- Marine & Chemical Processing: Corrosion-resistant heat exchangers in seawater cooling circuits and chemical reactor temperature control systems.
- Pharmaceutical & Medical: Temperature-controlled storage and processing equipment requiring hygienic-grade tubing with predictable thermal performance.
Quality Certifications & Standards
- ASTM A213: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for High-temperature Service
- ASTM A269: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Services
- ISO 3506: Fasteners made of stainless steel (applicable to coil tube fittings)
- EN 10217-7: Tubes and pipes of stainless steels and heat-resistant steels — Cold-drawn or cold-rolled tubes
- GB/T 12771: Chinese national standard for welded austenitic stainless steel tubes for general application
- NSF/ANSI 61: Drinking water system components certification (for food-grade applications)
- ISO 9001:2015: Quality Management System certification for manufacturing processes
Unique Selling Points
Thermally Characterized Performance: Wenzhou Jixing's coil tube products are distinguished by their empirically validated thermal resistance data across a defined range of ice accretion thicknesses (0–20 mm). This data-driven approach enables system designers to predict cooling performance degradation with high accuracy, reducing the need for iterative prototyping.
- Predictable Thermal Degradation Curve: Published $R_{th}$ vs. ice thickness relationships allow engineers to model system performance over the entire operational cycle of ice-based cooling systems.
- Superior Cryogenic Ductility: Austenitic stainless steel coil tubes maintain full mechanical integrity at temperatures as low as −196°C, with no risk of brittle fracture — a critical advantage over ferritic and martensitic alternatives.
- Extended Service Life: The combination of corrosion resistance, fatigue resistance from cold-worked microstructure, and resistance to ice adhesion (due to low surface energy of polished stainless steel) results in significantly longer replacement intervals.
- Customizable Geometry: Coil diameter, pitch, and tube dimensions can be tailored to specific thermal load requirements, enabling optimization of heat transfer area versus pressure drop trade-offs.
- Hygienic & Food-Safe: Polished surface finish (Ra ≤ 0.4 μm available) meets FDA and EU food contact material regulations, making the product suitable for pharmaceutical and food industry applications.
Thermal Resistance Analysis Summary
Based on experimental studies examining the effect of ice thickness on thermal resistance across coil tubes, ordinary ice balls, and core ice balls, the following conclusions are established for this product line:
- Thermal resistance increases approximately linearly with ice thickness for thin layers (0–5 mm), transitioning to a quasi-quadratic relationship beyond 10 mm due to the formation of porous ice structures with trapped air pockets.
- Coil tubes exhibit lower total thermal resistance compared to equivalent-volume ordinary ice balls, attributed to the higher surface-area-to-volume ratio and more uniform heat distribution along the helical path.
- Core ice ball configurations demonstrate the lowest thermal resistance of the three geometries studied, owing to their dual-phase (solid core + surrounding fluid) heat transfer mechanism.
- The stainless steel coil tube wall itself contributes a negligible thermal resistance component (typically < 0.001 °C·m²/W for wall thicknesses ≤ 1.5 mm), confirming that the dominant resistance lies in the ice layer and fluid-side convection.
This comprehensive thermal characterization data provides system designers with the quantitative foundation necessary for optimizing coil tube integration into any ice-based cooling application.