Stainless Steel Columnar Condensing Coil Tube — ASHP WH Application Series
Product Overview
The Stainless Steel Columnar Condensing Coil Tube (hereinafter referred to as "Coil Tube") is a precision-engineered heat exchange component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product Catalog No. 1077). This coil tube is specifically designed for integration into Air-Source Heat Pump (ASHP) Water Heater (WH) systems, where it functions as the primary condensing heat exchanger. The columnar coil geometry maximizes the surface-area-to-volume ratio within a confined cabinet footprint, enabling efficient condensation of refrigerant vapor and rapid transfer of latent heat to the water reservoir.
The design philosophy behind this coil tube is grounded in rigorous thermodynamic research, notably the study titled "Research on Water Temperature Distribution in ASHP WH Box Heated by Columnar Condensing Coil Tubes." This foundational research validated the superiority of columnar coil configurations over conventional serpentine or spiral arrangements in achieving uniform water temperature distribution, minimizing thermal stratification, and reducing dead zones within the water storage vessel.
Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, selected for its exceptional corrosion resistance, thermal conductivity, and long-term structural integrity under cyclic thermal loading conditions.
- Primary Material Grade: SUS304 (ASTM A269 TP304 / EN 1.4301) — a chromium-nickel austenitic stainless steel with a minimum nickel content of 8.0% and chromium content of 18.0%.
- Alternative Grade (for aggressive environments): SUS316 (ASTM A269 TP316 / EN 1.4401) — enhanced with 2.0–3.0% molybdenum for superior resistance to chloride-induced pitting corrosion.
- Thermal Conductivity: Approximately 16.3 W/(m·K) at 20°C (SUS304), providing efficient heat transfer from condensing refrigerant to water medium.
- Operating Temperature Range: −40°C to +180°C, accommodating both refrigerant-side and water-side thermal extremes.
- Surface Finish: Electropolished or passivated inner and outer surfaces (Ra ≤ 0.4 μm) to minimize fouling resistance and enhance heat transfer coefficients.
- Mechanical Properties: Tensile strength ≥ 520 MPa; Yield strength ≥ 205 MPa; Elongation ≥ 40% (per ASTM A269 standard).
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Catalog No. | 1077 | Wenzhou Jixing Internal Catalog |
| Tube Outer Diameter (OD) | Φ8.0 mm / Φ9.53 mm / Φ12.7 mm (configurable) | ASTM A269 / GB/T 12771 |
| Tube Wall Thickness | 0.5 mm – 1.0 mm (typical: 0.65 mm) | ASTM A269 Type 12 |
| Coil Pitch (Center-to-Center Spacing) | 15 mm – 30 mm (optimized for flow uniformity) | Custom engineering design |
| Coil Diameter (Columnar Form) | Φ200 mm – Φ400 mm (matched to WH cabinet dimensions) | Customer-specific |
| Total Tube Length (Uncoiled) | 20 m – 120 m (dependent on heat duty) | Thermodynamic calculation |
| Heat Transfer Surface Area | 12 m² – 55 m² | Based on OD × Length |
| Refrigerant Side Working Pressure | Up to 3.5 MPa (R410A / R32 / R134a compatible) | EN 378 / ISO 817 |
| Water Side Working Pressure | Up to 1.0 MPa | GB/T 12771 |
| End Connection Type | Flared / Brazed / Grooved / Threaded (NPT/BSP) | ISO 7 / ASME B1.20.1 |
| Surface Treatment | Electropolishing + Passivation | ASTM A967 |
| Hydrostatic Test Pressure | 1.5× Maximum Working Pressure (MWP) | GB/T 12771 Clause 7.3 |
| Weight (Typical, 50 m coil) | 4.5 kg – 7.2 kg | Material density: 8.0 g/cm³ |
Manufacturing Process
The production of the Stainless Steel Columnar Condensing Coil Tube follows a multi-stage precision manufacturing workflow to ensure dimensional accuracy, structural integrity, and surface quality:
- Raw Material Selection & Inspection: Stainless steel tubes conforming to ASTM A269 / GB/T 12771 are procured from certified suppliers. Incoming inspection includes chemical composition analysis (spectrometry), dimensional verification, and visual surface examination.
- Cold Drawing & Sizing: Tubes are cold-drawn to achieve precise outer diameter and wall thickness tolerances (±0.05 mm), ensuring uniform heat transfer characteristics along the entire tube length.
- Coil Winding (Columnar Configuration): Using CNC-controlled coiling machinery, the straight tube is wound into a columnar helical geometry with consistent pitch. The winding process is monitored by real-time laser displacement sensors to maintain pitch accuracy within ±0.3 mm.
- Support & Stabilization: Stainless steel or epoxy-coated support rings are welded at calculated intervals to prevent coil deformation under thermal cycling and pressure loading.
- End Forming & Connection Fabrication: Tube ends are formed (flared, grooved, or threaded) using precision tooling. Brazing or welding joints are performed under inert gas (Argon) shielding to prevent oxidation.
- Electropolishing & Passivation: The entire coil assembly undergoes electropolishing in an electrolytic bath to achieve a mirror-like surface finish (Ra ≤ 0.4 μm), followed by acid passivation to enhance the passive chromium oxide layer.
- Hydrostatic Pressure Testing: Each coil tube is pressure-tested at 1.5× MWP for a minimum of 60 seconds with zero leakage tolerance, ensuring zero-defect delivery.
- Final Inspection & Packaging: Non-destructive testing (eddy current or penetrant testing) is performed on weld joints. Products are packaged in protective foam-lined cartons with desiccant packs for moisture protection.
Applications
The Coil Tube is engineered for a range of demanding thermal applications:
- Air-Source Heat Pump Water Heaters (ASHP WH): Primary application. The columnar condensing coil tube serves as the refrigerant-to-water heat exchanger inside the insulated water storage cabinet, achieving rapid and uniform water heating.
- Commercial & Industrial Water Heating Systems: High-capacity ASHP units for hotels, hospitals, and food processing facilities requiring reliable, energy-efficient hot water supply.
- Domestic Heat Pump Systems: Residential ASHP water heaters with capacities ranging from 50 L to 300 L.
- Refrigeration Condensers: Secondary application in refrigeration and cold storage systems where stainless steel corrosion resistance is required (e.g., food-grade environments).
- Marine & Offshore Applications: High-chloride environments where SUS316 grade coil tubes provide extended service life.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing operations.
- ISO 14001:2015 — Environmental Management System certification.
- CE Marking — Conformity with European directives for pressure equipment (PED 2014/68/EU).
- GB/T 12771 — Chinese national standard for welded stainless steel tubes for heat exchangers.
- ASME B31.3 — Compliance with process piping code for pressure-containing heat exchangers.
- RoHS & REACH Compliance — Restriction of Hazardous Substances and chemical regulation compliance for export markets.
- NADCAP (if applicable for aerospace-adjacent applications) — Special process certification for welding and surface treatment operations.
Unique Selling Points
Research-Validated Columnar Geometry: Unlike conventional serpentine or spiral coil designs, the columnar configuration has been validated through published academic research on water temperature distribution within ASHP WH cabinets. This design minimizes thermal stratification, eliminates dead zones, and ensures uniform heating throughout the water volume — directly translating to faster heating cycles and improved COP (Coefficient of Performance) of the overall heat pump system.
- Optimized Pitch Engineering: Coil pitch is thermodynamically calculated for each application, balancing heat transfer efficiency against pressure drop and flow distribution uniformity.
- Full-Length Electropolished Surface: Industry-leading surface finish reduces fouling factors by up to 60%, maintaining design heat transfer performance over extended service intervals.
- Customization Capability: Flexible design parameters (tube OD, wall thickness, coil diameter, total length, end connections) allow precise matching to customer system requirements and cabinet dimensions.
- Zero-Leakage Guarantee: 100% hydrostatic testing at 1.5× MWP with documented traceability ensures absolute pressure integrity.
- Extended Service Life: SUS304/316 stainless steel construction provides corrosion resistance exceeding 25 years in standard water heating applications, significantly outperforming copper or aluminum alternatives in chloride-containing environments.
Technical Notes & Recommendations
For optimal system performance, the following engineering guidelines should be observed during system integration:
- Ensure adequate water-side flow velocity (0.5–1.5 m/s) to maintain turbulent flow and maximize convective heat transfer coefficients.
- Refrigerant-side inlet temperature should not exceed 180°C to avoid accelerated corrosion of the passive oxide layer.
- Install strainers upstream of the coil tube to prevent particulate fouling, especially in commercial systems with untreated water.
- Periodic visual inspection of the coil tube surface is recommended at 12-month intervals to detect any signs of localized corrosion or mechanical damage.
- For systems operating in environments with water hardness exceeding 300 ppm (as CaCO₃), consider integrating a water softening pre-treatment system to prevent scale deposition on the coil tube surface.