Stainless Steel Coil Tube (盘管) — Heat Pump Dual-Supply Heat Exchanger Application
1. Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component designed for use in heat pump dual-supply units (热泵两联供机组), where it functions as a critical heat exchange element. This coil tube is specifically engineered to address the industry-wide challenge of icing and freezing at the bottom of coil heat exchangers (盘管换热器底部结冰), a phenomenon that significantly degrades thermal efficiency, causes mechanical stress, and reduces service life in cold-climate operations.
Based on extensive research into the thermodynamic behavior of coil heat exchangers under low-temperature conditions, this product incorporates design modifications that ensure uniform heat distribution, minimize cold spots at the bottom section of the coil, and prevent frost accumulation — thereby extending operational reliability and energy efficiency.
2. Material & Properties
The coil tube is fabricated from high-purity stainless steel (不锈钢), selected for its superior corrosion resistance, thermal conductivity, and mechanical durability in demanding environmental conditions.
- Base Material: Austenitic stainless steel (奥氏体不锈钢), typically grades 304 (S30408) or 316L (S31603), conforming to ASTM A269 / EN 10216-5 / GB/T 14976 standards
- Corrosion Resistance: Excellent resistance to condensation water, de-icing agents, and humid ambient environments; chromium oxide passive layer provides long-term protection
- Thermal Conductivity: 14–16 W/(m·K) (304 grade); optimized for efficient heat transfer between refrigerant and water/air media
- Operating Temperature Range: −40 °C to +200 °C
- Mechanical Properties: Yield strength ≥ 205 MPa; tensile strength ≥ 515 MPa; elongation ≥ 40%
- Surface Finish: Electropolished or passivated inner surface (Ra ≤ 0.4 μm) to reduce fouling and minimize localized heat transfer resistance
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (盘管, Coiltube) |
| Product Code | No. 255 |
| Material Grade | ASTM 304 / 316L (customizable) |
| Outer Diameter (OD) | 8.0 – 25.4 mm (typical range; custom available) |
| Wall Thickness | 0.5 – 1.5 mm |
| Coil Diameter | 150 – 600 mm (customizable per application) |
| Tube Length (Uncoiled) | 5 – 50 m (standard); longer lengths available |
| Number of Turns | 10 – 200 turns (application-dependent) |
| End Form | Open ends, threaded ends, or flanged ends |
| Surface Treatment | Electropolished / Passivated / Brushed |
| Pressure Rating | Up to 1.6 MPa (design pressure; burst pressure ≥ 4.0 MPa) |
| Standards Compliance | ASTM A269, GB/T 14976, EN 10216-5, JIS G3459 |
| Customization | Available upon request (dimensions, material grade, end treatment) |
4. Manufacturing Process
- Material Selection & Inspection: Raw stainless steel seamless tubes are sourced from certified mills and subjected to spectroscopic analysis (Spectrometer), ultrasonic testing (UT), and visual inspection to verify chemical composition and absence of internal defects.
- Cutting & Deburring: Tubes are cut to specified lengths using precision saws and deburred internally and externally to ensure smooth fluid flow and prevent turbulence at entry points.
- Coil Forming (Bending): Tubes are cold-formed into coil configurations using CNC-controlled bending machines. The bending process is carefully controlled to avoid wall thinning, ovality, or micro-cracking, maintaining dimensional accuracy within ±0.5 mm tolerance.
- Heat Treatment (if applicable): For specific applications requiring enhanced mechanical properties, solution annealing (固溶退火) is performed at 1050–1100 °C followed by rapid water quenching to restore full austenitic microstructure.
- Surface Finishing: Electropolishing (电解抛光) is applied to the inner bore to achieve a smooth surface (Ra ≤ 0.4 μm), reducing scale formation and improving heat transfer efficiency. This is critical for preventing localized icing at the bottom of the coil.
- Assembly & Integration: Individual coils are assembled into multi-pass or multi-tube heat exchanger bundles with precise pitch and alignment to ensure uniform flow distribution and minimize dead zones where icing typically initiates.
- Final Testing: Each coil tube undergoes hydrostatic pressure testing (水压试验) at 1.5× design pressure, dimensional verification, and visual inspection to ensure full compliance with quality standards.
5. Applications
The stainless steel coil tube is specifically designed for the following application domains:
- Heat Pump Dual-Supply Units (热泵两联供机组): Primary application — used as the water-side heat exchange coil in cold water chiller / hot water boiler dual-function heat pumps, providing simultaneous cooling and heating. The anti-icing design ensures reliable operation even when ambient temperatures drop below 0 °C.
- Air-Source Heat Pumps (空气源热泵): Evaporator and condenser coil assemblies for residential and commercial air-source heat pump systems.
- Ground-Source Heat Pumps (地源热泵): Fluid-side heat exchanger coils in closed-loop geothermal systems.
- Commercial HVAC Systems (商用暖通空调系统): Chilled water coils, condensing coils, and fan coil units (FCU) for large-scale commercial buildings.
- Industrial Process Cooling/Heating: Precision temperature control in pharmaceutical, food processing, and chemical manufacturing.
- Anti-Frost Heat Exchanger Systems (防冻换热器系统): Specialized applications where bottom-coil icing prevention is a critical design requirement, such as cold-climate regions and unheated installation spaces.
6. Anti-Icing Design Features (Key Innovation)
Based on research findings from the study "Research on Preventing Icing at the Bottom of Coil Heat Exchangers in Heat Pump Dual-Supply Units" (基于热泵两联供机组防止盘管换热器底部易结冰研究), the following design innovations are incorporated:
- Optimized Flow Distribution: The coil geometry is designed to ensure uniform refrigerant and water flow across all turns, particularly at the bottom section, preventing stagnation zones where icing initiates.
- Enhanced Heat Transfer at Bottom Section: The bottom turns of the coil feature modified pitch spacing and increased tube density to maximize heat exchange area in the most susceptible icing region.
- Stainless Steel Material Advantage: The high thermal conductivity and anti-corrosion properties of stainless steel maintain consistent heat transfer performance even when exposed to condensation and de-icing cycles, unlike carbon steel alternatives that degrade over time.
- Smooth Surface Finish: Electropolished inner surfaces reduce nucleation sites for ice crystal formation, delaying the onset of frosting and improving overall defrost cycle efficiency.
- Structural Integrity: The seamless construction eliminates weld points that could become stress concentrators during freeze-thaw cycles, ensuring long-term reliability.
7. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring every coil tube product meets international standards:
- ISO 9001:2015 — Quality Management System Certification (质量管理体系认证)
- ISO 14001:2015 — Environmental Management System Certification (环境管理体系认证)
- CE Marking — European Conformity for safety and performance (欧洲合格认证)
- Material Test Reports (MTR): Full chemical composition and mechanical property reports provided with each batch
- Third-Party Inspection: Available upon request from SGS, TÜV, or equivalent accredited bodies
- Pressure Test Certificate: Hydrostatic test documentation included with each shipment
- Compliance Standards: ASTM A269, GB/T 14976, EN 10216-5, JIS G3459
8. Unique Selling Points (USPs)
- Research-Driven Anti-Icing Design: Product specifications are informed by dedicated academic research into bottom-coil icing prevention, offering a scientifically validated solution to a persistent industry problem.
- Premium Stainless Steel Construction: 304/316L grade material ensures decades of corrosion-free service life, even in harsh condensation and de-icing environments.
- Full Customization Capability: Dimensions, material grades, end treatments, and coil configurations are fully customizable to meet specific OEM and project requirements.
- End-to-End Quality Assurance: From raw material spectroscopic verification through final hydrostatic testing, every production stage is documented and traceable.
- Enhanced Energy Efficiency: Optimized coil geometry and smooth surface finish deliver superior heat transfer coefficients, reducing compressor runtime and lowering operational energy costs.
- Reliability in Extreme Conditions: Validated for continuous operation down to −40 °C without icing-related degradation, making it ideal for cold-climate installations.
9. Ordering Information
For technical inquiries, custom quotations, or sample requests, contact Wenzhou Jixing Metal Materials Co., Ltd. (温州市集兴金属材料有限公司). Product reference code: No. 255. All products are available in standard and custom configurations with full material traceability documentation.