Stainless Steel Spiral Coil Tube — Ground Source Heat Pump Heat Exchanger Series
Product Overview
The Stainless Steel Spiral Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchanger component specifically designed for Ground Water Source Heat Pump Systems (GSHP) and multi-row spiral coil heat exchangers. This product represents a high-efficiency solution for thermal energy transfer in geothermal heating and cooling applications, where compact geometry, superior heat exchange performance, and long-term corrosion resistance are critical engineering requirements.
Unlike conventional straight-tube heat exchangers, the spiral coil configuration maximizes the heat transfer surface area within a constrained volume, enabling enhanced thermal performance through induced secondary flow patterns and turbulent mixing. The coiltube geometry promotes a higher Nusselt number (h) and overall heat transfer coefficient (U), making it particularly advantageous for low-temperature differential applications such as ground-source heat pump systems.
Material Composition & Properties
The coil tubes are fabricated from high-grade austenitic stainless steel, selected for their exceptional resistance to corrosion, mechanical strength at elevated and sub-zero temperatures, and compatibility with groundwater and thermal fluid media.
- Primary Alloy Grades: SUS304 (AISI 304), SUS316L (AISI 316L), and SUS321 (AISI 321)
- Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and general acid attack in chloride-containing groundwater environments; SUS316L grade offers superior resistance due to molybdenum (Mo) content of 2.0–2.5%
- Thermal Conductivity: 14–16 W/(m·K) for 304 grade at 20°C, providing adequate thermal transfer performance
- Mechanical Strength: Yield strength ≥ 205 MPa (304), tensile strength ≥ 515 MPa; maintains ductility down to cryogenic temperatures
- Operating Temperature Range: −196°C to +870°C (304 grade); −270°C to +800°C (316L grade)
- Surface Finish: Electropolished (Ra ≤ 0.4 μm) or brushed finish for reduced fouling and improved hydraulic efficiency
Technical Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 12 mm, 16 mm, 19 mm, 22 mm, 25 mm, 32 mm (customizable) |
| Wall Thickness | 0.5 mm – 1.5 mm (depending on pressure rating and application) |
| Spiral Pitch | 20 mm – 50 mm (adjustable per heat exchanger design requirements) |
| Coil Diameter | 100 mm – 500 mm (coil-to-coil distance configurable) |
| Tube Length (per coil) | 5 m – 30 m (custom lengths available) |
| Maximum Working Pressure | 1.6 MPa – 4.0 MPa (based on wall thickness and OD) |
| Design Temperature | −40°C to +200°C (standard); up to +400°C for specialized applications |
| Multi-Row Configuration | 1-row to 6-row spiral coil arrangements (as per GSHP heat exchanger design) |
| Connection Type | Welded (TIG/argon arc), flanged, or threaded fittings |
| Surface Treatment | Pickling, passivation, electropolishing, or PTFE coating (optional) |
| Standards Compliance | GB/T 14976, GB/T 21830, ASTM A269, ASTM A270, EN 10217, ISO 3506 |
Manufacturing Process
The production of stainless steel spiral coil tubes follows a rigorous, multi-stage manufacturing protocol to ensure dimensional accuracy, structural integrity, and consistent material properties:
- Material Selection & Incoming Inspection: Cold-rolled stainless steel coils are procured from certified suppliers and subjected to spectroscopic analysis (PMI — Positive Material Identification), hardness testing, and visual inspection to verify compliance with specified alloy chemistry.
- Hydroforming / Coil Forming: The straight tube is formed into a precise spiral geometry using CNC-controlled hydroforming machines or hydraulic coil-bending equipment. The forming process is conducted under controlled temperature and speed parameters to prevent material strain hardening, cracking, or dimensional deviation.
- Heat Treatment (if required): Solution annealing at 1050–1100°C followed by water quenching may be applied to restore full austenitic microstructure and eliminate residual stresses introduced during forming.
- Welding & Assembly: Multi-row coil bundles are assembled and connected via TIG (Tungsten Inert Gas) welding with argon shielding. All welds undergo 100% visual inspection and are subjected to helium leak testing (detection sensitivity: 1×10⁻⁹ Pa·m³/s) to ensure zero leakage.
- Surface Treatment: Tubes undergo acid pickling and passivation to remove oxide scale and form a stable chromium oxide protective layer. Electropolishing may be applied for ultra-clean surface requirements.
- Final Testing: Each coil tube undergoes hydrostatic pressure testing at 1.5× working pressure, dimensional verification via CMM (Coordinate Measuring Machine), and non-destructive testing (NDT) as applicable.
Applications
The multi-row stainless steel spiral coil tube heat exchanger is specifically engineered for the following applications:
- Ground Water Source Heat Pump Systems (GSHP): Primary application — the coil tube serves as the core heat exchange element in borehole or aquifer-based ground heat exchangers, transferring thermal energy between the working fluid and groundwater with minimal pressure drop and maximum heat transfer efficiency.
- Geothermal Energy Extraction: Deep-well heat exchangers for renewable energy systems utilizing subsurface thermal gradients.
- Industrial Process Heating & Cooling: Compact heat recovery units in chemical processing, food and beverage manufacturing, and pharmaceutical production where hygienic-grade stainless steel is mandated.
- Marine & Offshore Applications: Corrosion-resistant heat exchangers for seawater cooling systems and shipboard HVAC units.
- HVAC Systems: High-efficiency compact coil units for commercial and industrial air handling systems requiring enhanced thermal performance in limited installation spaces.
- Food & Dairy Processing: Sanitary-grade heat exchangers for pasteurization, sterilization, and thermal processing of perishable products.
Quality Certifications & Standards
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — European Conformity for pressure equipment (PED 2014/68/EU)
- TÜV Certification — Third-party product conformity assessment
- EN 10204 3.1 Certificate — Material test reports with independent inspection
- ASME Stamp (U/UR) — For pressure vessel and heat exchanger components (where applicable)
- NSF/ANSI 61 — Drinking water system component certification (for potable water applications)
- GB/T 19001 — Chinese national quality management standard
Unique Selling Points
1. Superior Heat Transfer Efficiency: The spiral coil geometry induces Dean vortices and secondary flow patterns that significantly enhance turbulent mixing, resulting in a 20–40% improvement in heat transfer coefficient compared to equivalent straight-tube designs.
2. Compact Design: High surface-area-to-volume ratio enables compact heat exchanger assemblies, reducing installation footprint and minimizing material usage while maximizing thermal capacity.
3. Exceptional Corrosion Resistance: SUS316L-grade stainless steel with molybdenum alloying provides outstanding resistance to chloride-induced pitting in groundwater environments, ensuring service life exceeding 25 years without replacement.
4. Low Pressure Drop: Optimized spiral pitch and coil diameter configurations minimize hydraulic resistance, reducing pumping energy consumption in GSHP systems by up to 15%.
5. Multi-Row Configurations: Customizable 1-row through 6-row coil arrangements allow precise tuning of thermal performance to match specific GSHP system design parameters and load requirements.
6. Full Traceability: Each product is accompanied by mill test certificates, heat numbers, and complete traceability documentation in compliance with EN 10204 and ISO 9001 requirements.
Performance Characteristics — Multi-Row Spiral Coil Heat Exchanger
Based on research into multi-row spiral coil heat exchanger performance in ground water source heat pump systems, the following performance benchmarks have been established for this product line:
| Performance Metric | Typical Value | Conditions |
|---|---|---|
| Overall Heat Transfer Coefficient (U) | 1,200 – 2,500 W/(m²·K) | Water-water, 15–35°C flow range |
| Heat Transfer Efficiency (ε) | 75% – 92% | NTU (Number of Transfer Units) = 2.0 – 4.0 |
| Pressure Drop (ΔP) | 15 – 45 kPa | Flow velocity 1.5 – 3.0 m/s |
| COP Improvement (GSHP) | 5% – 12% vs. conventional designs | Groundwater temperature 12–18°C |
| Fouling Factor | 0.00008 – 0.00015 m²·K/W | Electropolished surface, treated groundwater |
This product line represents the culmination of advanced metallurgical engineering and thermal-fluid dynamics research, delivering a reliable, high-performance solution for the growing global demand for sustainable geothermal heating and cooling systems.