Stainless Steel Coil Tube — Evaporative Cooling Grade
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Catalog Reference: No. 1004
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. specifically designed for high-performance heat exchange and evaporative cooling applications. Unlike conventional straight-length stainless steel tubes, coil tubes are formed into continuous helical or spiral configurations that dramatically increase the surface-area-to-volume ratio, thereby enhancing convective and conductive heat transfer efficiency. This product line has been extensively validated through rigorous mathematical modeling of heat transfer and mass transfer characteristics in coil-tube evaporative coolers, confirming its superior thermal performance in demanding industrial environments.
The coil tube geometry facilitates turbulent flow regimes at lower Reynolds numbers compared to straight tubes, reducing fouling accumulation and maintaining consistent thermal conductivity over extended operational cycles. Wenzhou Jixing Metal Materials Co., Ltd. leverages advanced metallurgical expertise and precision forming technology to deliver coil tubes that meet the exacting standards of HVAC (Heating, Ventilation, and Air Conditioning), industrial refrigeration, and process cooling sectors.
2. Material & Properties
2.1 Base Material Grades
- Austenitic Stainless Steel: ASTM A269 / ASME SA-269 — Grade 304 (UNS S30400) and Grade 316 (UNS S31600)
- High-Nickel Austenitic Grades: Grade 316L (UNS S31603), Grade 321 (UNS S32100), Grade 347 (UNS S34700)
- Duplex Stainless Steel: Grade 2205 (UNS S32205) for elevated pressure and corrosion-resistance requirements
- Custom Alloy Compositions: Available upon request for specialized thermal and chemical environments
2.2 Key Physical and Mechanical Properties
| Property | Grade 304 (UNS S30400) | Grade 316L (UNS S31603) | Grade 2205 (UNS S32205) |
|---|---|---|---|
| Thermal Conductivity (W/m·K) at 20 °C | 16.3 | 14.6 | 10.0 |
| Density (kg/m³) | 7930 | 8000 | 7810 |
| Specific Heat Capacity (J/kg·K) | 500 | 500 | 480 |
| Yield Strength (MPa, minimum) | 205 | 170 | 450 |
| Tensile Strength (MPa, minimum) | 515 | 485 | 620 |
| Maximum Service Temperature (°C) | 870 | 870 | 320 |
| Corrosion Resistance (Pitting, PREN) | 18–20 | 24–26 | 34–38 |
| Crystal Structure | Austenitic (FCC) | Austenitic (FCC) | Duplex (FCC + BCC) |
2.3 Surface Finish Options
- Commercial (No. 1) Finish: Hot-rolled and annealed; suitable for industrial applications where appearance is secondary
- 2B Finish: Cold-rolled and annealed; balanced surface quality for general heat exchanger use
- BA (Bright Annealed) Finish: Polished to 0.02–0.05 μm Ra; ideal for food-grade and pharmaceutical cooling
- Electropolished Finish: Ra ≤ 0.025 μm; critical for bioprocessing and ultra-pure fluid systems
3. Specifications
3.1 Dimensional Parameters
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.175 mm – 114.3 mm (⅛" – 4") | ASTM A269 / ASME SA-269 |
| Wall Thickness (WT) | 0.25 mm – 8.0 mm (0.010" – 0.315") | ASTM A269 / ASME SA-269 |
| Coil Pitch (Helical Spacing) | 5 mm – 50 mm (customizable) | ISO 21979 |
| Coil Mean Diameter (CMD) | 50 mm – 500 mm | Manufacturer Specification |
| Number of Turns | 1 – 200+ (as required by application) | Customer-Specific |
| Coil Length (Developed) | 1 m – 100 m (continuous coil) | Customer-Specific |
| End Form | Flat-cut, beveled, threaded, or flanged | ASME B1.20.1 / B16.5 |
| Dimensional Tolerance (OD) | ±0.05 mm to ±0.50 mm (per order) | ISO 1128 |
| Dimensional Tolerance (WT) | ±5% to ±10% (per order) | ASTM A269 |
| Roundness | ≤ 0.5% of OD | ISO 4977 |
3.2 Performance Characteristics
| Performance Metric | Typical Value / Range | Measurement Standard |
|---|---|---|
| Overall Heat Transfer Coefficient (U) | 800 – 2,500 W/m²·K | ASHRAE Handbook — Heat Transfer |
| Enhancement Factor vs. Straight Tube (h) | 1.3 – 2.8× | Mathematical modeling (Nusselt correlation) |
| Pressure Drop (ΔP) per Meter | 50 – 500 Pa/m (flow-dependent) | Darcy-Weisbach equation |
| Reynolds Number at Transition (Re) | 2,100 – 4,000 (geometry-dependent) | ISO 4326 |
| Maximum Operating Pressure | Up to 40 MPa (grade-dependent) | ASME BPV Code VIII |
| Operating Temperature Range | −196 °C to +870 °C | Material-specific |
| Mass Transfer Coefficient Enhancement | 1.2 – 2.5× vs. straight tube | Chilton-Colburn analogy |
4. Manufacturing Process
Wenzhou Jixing Metal Materials Co., Ltd. employs a multi-stage, quality-controlled manufacturing process to produce stainless steel coil tubes that meet the highest industry standards:
4.1 Process Flow
- Raw Material Selection and Inspection: High-purity stainless steel strip or seamless tube stock is sourced from certified mills. Incoming materials undergo spectroscopic analysis (OES — Optical Emission Spectroscopy), tensile testing, and visual inspection to verify chemical composition and mechanical properties per ASTM A269 / EN 10217 standards.
- Coil Forming (Cold Drawing / Rotary Bending): The tube stock is fed through a series of precisely aligned forming rollers or rotary bending dies to create the helical coil geometry. Computer Numerical Control (CNC) systems ensure consistent coil pitch, mean diameter, and turn-to-turn accuracy within ±0.5 mm tolerance.
- Heat Treatment (Annealing): Formed coils undergo solution annealing at 1010–1120 °C followed by controlled cooling to restore full austenitic microstructure, relieve residual stresses introduced during forming, and maximize corrosion resistance and ductility.
- Pickling and Passivation: Annealed coils are subjected to acid pickling (nitric/hydrofluoric acid blend) to remove scale and oxide films, followed by passivation to restore the protective chromium oxide layer. This step is critical for ensuring long-term corrosion performance in evaporative cooling environments.
- Surface Finishing: Depending on the application specification, coils receive 2B, BA, or electropolished finishes. Electropolishing involves electrochemical dissolution to achieve sub-0.025 μm Ra surface roughness, essential for hygienic and pharmaceutical cooling applications.
- Precision Cutting and End Finishing: Coils are cut to required lengths using laser or waterjet cutting to prevent work hardening and deformation. End preparations include flat cuts, bevels (per ASME B16.25), thread forming (per ASME B1.20.1), or flange welding (per ASME B16.5).
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Quality Control and Testing: Every batch undergoes comprehensive non-destructive testing (NDT), including:
- Helical Eddy Current Testing (per ASTM E309 / ASTM E2134) for internal and external defect detection
- Hydrostatic Pressure Testing (per ASTM A269) at 1.5× working pressure for a minimum of 30 seconds
- Dimensional verification using coordinate measuring machines (CMM) and optical profilometry
- Surface roughness measurement (per ISO 4287) to confirm finish specifications
- Packaging and Dispatch: Certified coils are packaged in protective wooden crates or shrink-wrapped pallets with desiccant inserts to prevent corrosion during transit. Each shipment includes a mill test certificate (MTC) per EN 10204 Type 3.1.
5. Applications
5.1 Primary Application Domains
- Evaporative Cooling Systems: The coil tube geometry is specifically optimized for evaporative coolers, where mathematical modeling of heat and mass transfer confirms enhanced performance. The helical configuration promotes turbulent flow and maximizes the interfacial area between the cooling medium and the tube wall, achieving overall heat transfer coefficients of 800–2,500 W/m²·K.
- HVAC (Heating, Ventilation, and Air Conditioning): Used in condenser and evaporator coils for commercial and industrial air conditioning units, chillers, and heat pumps. The corrosion resistance of austenitic grades ensures long service life in humid and chemically aggressive environments.
- Industrial Refrigeration: Deployed in ammonia, CO₂ (transcritical), and hydrofluorocarbon (HFC) refrigeration systems where high thermal efficiency and pressure containment are critical.
- Food and Beverage Processing: BA and electropolished coil tubes are used in pasteurization, sterilization, and refrigeration systems for dairy, beverage, and pharmaceutical production, meeting FDA and EU 1935/2004 compliance requirements.
- Chemical and Petrochemical Processing: Grade 316L and duplex 2205 coil tubes handle corrosive process streams, acid cooling loops, and heat recovery systems in refineries and chemical plants.
- Power Generation: Applied in waste heat recovery, condenser tubes, and cooling water circuits in thermal power plants and combined heat and power (CHP) systems.
- Marine and Offshore Applications: Duplex stainless steel coil tubes resist chloride-induced pitting and crevice corrosion in seawater cooling systems for ships and offshore platforms.
- Aerospace and Defense: High-temperature and high-pressure coil tubes for environmental control systems (ECS) and hydraulic fluid cooling in aircraft and ground vehicles.
5.2 Thermal Performance Validation
The application of coil tubes in evaporative cooling systems has been validated through rigorous mathematical modeling that accounts for coupled heat transfer and mass transfer phenomena. The governing equations incorporate:
- Energy Balance: Conservation of enthalpy across the coil-tube control volume, accounting for sensible and latent heat exchange between the working fluid and the evaporating water film.
- Momentum Balance: Darcy-Weisbach friction factor correlations adapted for helical geometry, including Dean number (De) effects that characterize secondary flow patterns in curved tubes.
- Mass Transfer: Sherwood number correlations derived from the Chilton-Colburn analogy, relating convective mass transfer of water vapor to the cooling surface.
- Boundary Conditions: Wet-bulb temperature boundary conditions at the coil surface, coupled with psychrometric properties of the ambient air stream.
These models confirm that coil-tube evaporative coolers achieve cooling efficiencies 15–30% higher than equivalent straight-tube designs at comparable pressure drops, validating the geometric advantage of the helical configuration.
6. Quality Certifications
6.1 International Standards and Certifications
| Certification / Standard | Scope of Compliance | Issuing Body |
|---|---|---|
| ISO 9001:2015 | Quality Management System — full manufacturing process | ISO / Accredited Certification Body |
| ISO 14001:2015 | Environmental Management System — sustainable manufacturing | ISO / Accredited Certification Body |
| ISO 45001:2018 | Occupational Health and Safety Management | ISO / Accredited Certification Body |
| AS |