Stainless Steel Dry Coil Tube for Air Conditioning Systems
Product Overview
The Stainless Steel Dry Coil Tube (hereinafter referred to as "Coil Tube") is a precision-engineered heat exchanger component designed specifically for dry-air total heat recovery systems in commercial and industrial air conditioning applications. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 469), this coil tube serves as the core heat transfer element in dry coil air conditioning systems (干盘管空调系统), enabling efficient latent heat removal from incoming fresh air while maintaining minimal energy consumption.
Unlike conventional cooling coils that rely on evaporative cooling to dehumidify air, the dry coil tube operates at temperatures above the dew point of the process air, utilizing refrigerant circulation to absorb latent moisture without overcooling. This design philosophy—rooted in thermodynamic optimization—significantly reduces the reheat energy penalty commonly associated with traditional sensible-plus-latent cooling approaches. The coil tube is particularly advantageous in office building ventilation systems where maintaining indoor relative humidity within ASHRAE-recommended ranges (40–60%) is critical for occupant comfort and indoor air quality (IAQ).
The product is engineered to integrate seamlessly with variable refrigerant flow (VRF) systems, chiller-driven hydronic loops, and standalone refrigeration circuits, offering versatile deployment across diverse architectural HVAC configurations.
Material & Properties
Base Material Composition
The coil tube is fabricated from high-purity austenitic stainless steel, conforming to the following material specifications:
- Primary Alloy: SUS304 / AISI 304 (06Cr19Ni10) — Chromium-Nickel austenitic stainless steel
- Alternative Grade: SUS316L / AISI 316L (022Cr17Ni12Mo2) — Molybdenum-enhanced austenitic stainless steel for aggressive environments
- Reinforced Option: SUS321 (06Cr18Ni11Ti) — Titanium-stabilized grade for high-temperature service
Mechanical Properties
- Tensile Strength (UTS): 520–750 MPa (75,000–109,000 psi)
- Yield Strength (0.2% offset): 205–310 MPa (30,000–45,000 psi)
- Elongation at Break: ≥ 40% (indicating excellent formability for coiling)
- Hardness (Brinell): 150–210 HB
- Impact Strength (Charpy V-Notch, 20°C): ≥ 70 J (superior cold-work fracture resistance)
Thermal Properties
- Thermal Conductivity (λ): 14.5–16.5 W/(m·K) at 20°C
- Specific Heat Capacity (cp): 500 J/(kg·K) at 25°C
- Thermal Expansion Coefficient (α): 17.3 × 10-6 /K (linear, 20–100°C)
- Operating Temperature Range: −196°C to +450°C (continuous service)
Corrosion Resistance
The austenitic stainless steel matrix provides exceptional resistance to:
- Atmospheric Corrosion: Passive chromium oxide film (Cr2O3) self-heals in oxygen-containing environments
- Chemical Resistance: Immune to dilute acids, alkalis, and most organic solvents
- Pitting Resistance (PREN): SUS316L achieves a Pitting Resistance Equivalent Number (PREN) of ≥ 26, suitable for chloride-rich or humid indoor air
- Intergranular Corrosion: Low-carbon (L-grade) variants resist sensitization during welding
Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Outer Diameter (OD) | Φ9.52 / Φ12.7 / Φ15.88 / Φ19.05 (customizable) | mm |
| Wall Thickness (T) | 0.50 / 0.65 / 0.80 / 1.00 | mm |
| Inner Diameter (ID) | Φ8.52 / Φ11.70 / Φ14.88 / Φ18.05 | mm |
| Coil Pitch (Center-to-Center) | 12 / 15 / 18 / 20 / 25 | mm |
| Row Configuration | 2-Row / 3-Row / 4-Row / 6-Row | — |
| Tube Length per Row | 300 / 600 / 900 / 1200 / 1800 / 2400 | mm |
| Overall Coil Dimensions (W × H) | Up to 2000 × 1500 | mm |
| Refrigerant Flow Rate (Typical) | 0.5 – 3.0 | L/min |
| Air-Side Velocity (Recommended) | 1.5 – 3.0 | m/s |
| Refrigerant Side Pressure (Max) | 2.5 (R410A) / 1.8 (R22) / 2.0 (R134a) | MPa |
| Design Service Life | ≥ 25 | Years |
| Weight (Typical, 600×600, 4-Row) | 3.2 – 5.8 | kg |
| Surface Treatment | Passivated / Electropolished / Coated (PTFE optional) | — |
Manufacturing Process
The production of precision stainless steel coil tubes follows a rigorous multi-stage manufacturing protocol designed to ensure dimensional accuracy, metallurgical integrity, and consistent thermal performance:
Stage 1: Raw Material Procurement & Inspection
- Hot-rolled stainless steel strip (SUS304/316L) is sourced from certified mills with full mill test certificates (MTC) compliant with ASTM A270 / EN 10217-7 standards
- Incoming material undergoes spectroscopic verification (OES — Optical Emission Spectroscopy) to confirm chemical composition within tolerance bands
- Hardness testing (Rockwell B) and tensile sampling per ASTM E8 ensure mechanical conformity
Stage 2: Cold Forming & Tube Drawing
- Flat strip is precision-formed into seamless circular tubing via rotary swaging or hydroforming, achieving tight tolerances (± 0.05 mm on OD)
- Cold drawing imparts beneficial work-hardening effects, enhancing fatigue resistance and yield strength by approximately 15–25% compared to annealed condition
- Intermediate annealing (1050–1150°C, solution treatment) is performed at defined intervals to prevent excessive strain hardening and restore ductility
Stage 3: Coil Winding & Fin Application
- Formed tubes are wound into serpentine coil patterns using CNC-controlled coiling machines, maintaining precise pitch uniformity (± 0.3 mm tolerance)
- High-performance aluminum fins (alloy 1100 or 3003) are mechanically bonded to the stainless steel tubes via a proprietary fin-stamping and crimping process
- Fin density is optimized at 10–14 FPI (Fins Per Inch) to balance heat transfer surface area against air-side pressure drop
- Hydrophilic coating (fluoropolymer-based) is optionally applied to fins to enhance latent heat transfer efficiency during dehumidification cycles
Stage 4: Brazing & Header Assembly
- Tube ends are brazed to stainless steel or copper headers using phosphorus-free filler alloys (e.g., Ni-Fe-P type) to prevent galvanic corrosion at dissimilar metal joints
- Brazing is performed in a controlled nitrogen atmosphere (dew point ≤ −40°C) to minimize oxide formation and ensure hermetic seals
- Post-braze passivation (citric acid or nitric acid bath) restores the protective chromium oxide layer on all exposed surfaces
Stage 5: Quality Control & Testing
- Dimensional Inspection: CMM (Coordinate Measuring Machine) verification of coil geometry, pitch, and header alignment
- Pressure Testing: Hydrostatic pressure test at 1.5× maximum design pressure (held for 10 minutes, zero leakage tolerance)
- Leak Detection: Helium mass spectrometer leak testing at sensitivity level of 1 × 10-9 Pa·m³/s
- Thermal Performance Verification: Sample coils are tested in a calibrated wind tunnel per ASHRAE Standard 16 — measuring total heat transfer coefficient (U-value), air-side pressure drop (ΔP), and dew point depression
- Corrosion Testing: Salt spray test per ASTM B117 (≥ 1000 hours, no red rust) and immersion testing in simulated indoor air condensate
Applications
Primary Application: Dry Coil Fresh Air Treatment Systems
The defining application of this coil tube is in dry coil air conditioning systems (干盘管空调系统) for office buildings and commercial facilities. In this configuration, the coil tube absorbs latent heat from incoming outdoor air, effectively dehumidifying the airstream without significant sensible cooling. Key benefits include:
- Energy Efficiency: Eliminates the reheat energy penalty associated with overcooling-and-reheating cycles, achieving energy savings of 20–35% compared to conventional systems
- Superior IAQ: Maintains precise humidity control (± 5% RH), preventing mold growth and enhancing occupant comfort
- Comfort Enhancement: Avoids cold drafts and temperature stratification common with evaporative coils operating below dew point
Additional Applications
- Commercial Office Buildings: Fresh air handling units (AHU) and dedicated outdoor air systems (DOAS) in Class A office towers
- Hospital & Laboratory HVAC: Critical environments requiring stringent humidity and cleanliness control (ISO 14644 compliant)
- Data Centers: Precision cooling for server rooms where latent load management is essential
- Pharmaceutical & Food Processing: Cleanroom air conditioning where stainless steel material integrity is mandatory (FDA/USP Class VI compliant)
- Marine & Offshore Platforms: HVAC systems in corrosive salt-air environments where SUS316L grade provides long-term durability
- Industrial Process Cooling: Chilled water loops for precision temperature control in manufacturing facilities
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring every coil tube product meets international standards:
- ISO 9001:2015 — Quality Management Systems certification covering all manufacturing processes
- ISO 14001:2015 — Environmental Management Systems, demonstrating sustainable manufacturing practices
- ISO 45001:2018 — Occupational Health and Safety Management Systems
- CE Marking (EU) — Conformity with European directives for pressure equipment (PED 2014/68/EU) and machinery safety
- EN 12828 — Compliance with European standard for components of heating systems
- ASTM A270 — Standard specification for wrought austenitic stainless steel tubing for general applications
- GB/T 12771 — Chinese national standard for welded stainless steel tubing (where applicable)
- ASHRAE Standard 16 — Thermal performance testing and rating methodology for air-cooled heat exchangers
- NSF/ANSI 61 — Drinking water system components certification (for hydronic coil applications)
- RoHS 2.0 Compliance — Restriction of hazardous substances in electrical/electronic equipment
Unique Selling Points
1. Superior Thermal Efficiency: The precision-engineered coil geometry and optimized fin density achieve a total heat transfer coefficient (U-value) exceeding 60 W/(m²·K) in typical dry coil configurations, outperforming standard copper-tube alternatives by 10–15%.
2. Exceptional Durability: The all-stainless-steel construction eliminates the galvanic corrosion risk inherent in copper-aluminum coil assemblies, extending service life to 25+ years without degradation of heat transfer surfaces.
3. Customizable Configurations: Wenzhou Jixing offers fully customizable coil dimensions, row counts, fin densities, and refrigerant circuit arrangements, enabling precise matching to any HVAC system design requirement.
4. Low-Maintenance