Stainless Steel Coil Tube — Refrigerant Evaporation Application Series
Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this precision-engineered stainless steel coil tube (盘管 / Coiltube) is purpose-designed for advanced refrigeration and heat exchange systems, particularly those employing refrigerant jet evaporation technology within evaporating coil tube configurations. The product represents a convergence of metallurgical excellence and thermal engineering innovation, delivering superior performance in demanding cryogenic and HVAC (Heating, Ventilation, and Air Conditioning) environments.
Product Overview
The stainless steel coil tube is a continuous, helically wound tubular component fabricated from high-grade austenitic stainless steel alloys. Unlike conventional straight-pipe heat exchangers, the coil geometry provides an exceptionally high surface-area-to-volume ratio, enabling efficient heat transfer in compact footprints. This product line is specifically optimized for integration into refrigeration systems where refrigerant jet evaporation is utilized to enhance evaporative heat transfer coefficients and reduce the thermodynamic irreversibility of the phase-change process.
The coil tube configuration allows refrigerant to flow through a compact, spirally wound channel, promoting turbulent flow regimes at relatively low Reynolds numbers. This turbulence intensification is critical for jet evaporation systems, where controlled refrigerant injection into the coil tube generates micro-scale boiling phenomena that dramatically improve heat transfer rates compared to conventional flooded or dry-expansion evaporators.
Unique Selling Points
- Superior Corrosion Resistance: Austenitic stainless steel construction provides exceptional resistance to chloride-induced pitting, intergranular corrosion, and general oxidation, ensuring long service life even in aggressive refrigerant environments (e.g., ammonia, hydrofluorocarbons, and hydrofluoroolefins).
- Compact Helical Geometry: The coil design maximizes heat exchange surface area within minimal spatial volume, reducing the overall system footprint by up to 40% compared to equivalent shell-and-tube configurations.
- Enhanced Turbulence Characteristics: The curved flow path generates secondary Dean vortices that promote radial mixing, eliminating thermal boundary layer stagnation and improving evaporative heat transfer coefficients by 25–35%.
- Thermal Stability: Maintains dimensional and mechanical integrity across extreme temperature ranges from −60 °C to +180 °C, critical for cryogenic refrigeration applications.
- Hygienic Surface Finish: Available in electropolished or passivated finishes with surface roughness as low as Ra ≤ 0.4 μm, meeting pharmaceutical and food-grade sanitary standards.
- Weld-Free or Precision-Welded Configurations: Seamless coil tubes eliminate internal weld seams that could act as nucleation sites for corrosion or flow disruption.
Material & Properties
Base Alloy Grades
The coil tubes are manufactured primarily from the following austenitic stainless steel grades, each selected for specific performance requirements:
| Property | 304 / 0Cr18Ni9 | 316 / 0Cr17Ni12Mo2 | 316L / 00Cr17Ni14Mo2 | 321 / 0Cr18Ni11Ti |
|---|---|---|---|---|
| Chromium (Cr) | 18.0–20.0 % | 16.0–18.0 % | 16.0–18.0 % | 17.0–19.0 % |
| Nickel (Ni) | 8.0–10.5 % | 10.0–14.0 % | 12.0–14.5 % | 9.0–12.0 % |
| Molybdenum (Mo) | — | 2.0–3.0 % | 2.0–3.0 % | — |
| Titanium (Ti) | — | — | — | 5×C to 0.7 % |
| Carbon (C, max) | 0.08 % | 0.08 % | 0.03 % | 0.08 % |
| Density (kg/m³) | 7,930 | 8,000 | 8,000 | 7,900 |
| Thermal Conductivity (W/m·K, at 20 °C) | 16.3 | 14.6 | 14.6 | 16.3 |
| Thermal Conductivity (W/m·K, at 100 °C) | 21.5 | 20.2 | 20.2 | 21.5 |
| Specific Heat (J/kg·K, at 20 °C) | 500 | 500 | 500 | 500 |
| Tensile Strength (MPa, min) | 520 | 520 | 450 | 520 |
| Yield Strength (MPa, min) | 205 | 205 | 170 | 205 |
| Elongation (% of gauge length, min) | 40 | 40 | 35 | 40 |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 | −196 to +870 | −196 to +900 |
| Pitting Resistance (PREN*) | 18–20 | 24–26 | 24–26 | 18–20 |
*PREN = Pitting Resistance Equivalent Number = %Cr + 3.3×%Mo + 16×%N
Key Material Characteristics
- Non-magnetic: Austenitic microstructure ensures non-magnetic properties, eliminating interference with adjacent magnetic sensors or actuators in refrigeration control systems.
- Weldability: Excellent hot and cold workability permits fabrication of complex coil geometries and reliable TIG (Tungsten Inert Gas) or orbital welding of end connections without sensitization concerns in low-carbon grades (304L, 316L).
- Creep Resistance: Grade 321 with titanium stabilization offers superior resistance to intergranular corrosion at elevated temperatures, suitable for high-pressure refrigerant circuits.
- Passivation: Self-forming chromium oxide (Cr₂O₃) passive film provides inherent corrosion protection, with film thickness of 2–5 nm, effectively isolating the base metal from corrosive refrigerant species.
Specifications
Geometric Dimensions
| Parameter | Typical Range | Notes |
|---|---|---|
| Outer Diameter (OD) | 3 mm – 50 mm | Custom diameters available upon request |
| Wall Thickness | 0.3 mm – 3.0 mm | Thinner walls for cryogenic; thicker for high-pressure |
| Coil Pitch (helix spacing) | 5 mm – 25 mm | Determines surface density and flow resistance |
| Coil Mean Diameter | 25 mm – 500 mm | Adaptable to heat exchanger housing dimensions |
| Total Coil Length | 0.5 m – 20 m | Continuous or segmented configurations |
| Number of Turns | 10 – 500 | Calculated based on thermal duty requirements |
| End Configuration | Plain, threaded, flanged, or socket-weld | Per customer specification |
| Surface Finish (internal) | Ra 0.4 – 1.6 μm | Electropolished for sanitary applications |
| Surface Finish (external) | Ra 0.8 – 3.2 μm | Brushed, polished, or as-rolled |
| Pressure Rating (design) | 0.5 MPa – 15 MPa | Dependent on OD, wall thickness, and grade |
| Tolerance on OD | ±0.05 mm – ±0.20 mm | Per ASTM A213 / ASME B36.19M |
| Tolerance on Wall Thickness | ±10 % of nominal | Per ASTM A269 |
Performance Parameters for Refrigerant Evaporation
| Parameter | Value / Range | Test Conditions |
|---|---|---|
| Evaporative Heat Transfer Coefficient | 1,500 – 5,500 W/m²·K | R134a, inlet quality 0.1–0.9, mass flux 50–300 kg/m²·s |
| Pressure Drop per Unit Length | 50 – 400 Pa/m | Refrigerant flow, depending on OD and velocity |
| Overall Heat Transfer Coefficient (U-value) | 800 – 3,200 W/m²·K | Refrigerant-to-air or refrigerant-to-water |
| Refrigerant Compatibility | R134a, R410A, R404A, R507A, NH₃, CO₂ (R744) | Verified for long-term chemical compatibility |
| Maximum Operating Pressure | 15 MPa (2175 psi) | Grade 316L, OD 12 mm, wall 1.5 mm |
| Cycle Life (thermal fatigue) | >100,000 cycles | −40 °C to +60 °C cycling |
Manufacturing Process
The production of precision stainless steel coil tubes follows a rigorous, multi-stage manufacturing protocol designed to ensure dimensional accuracy, metallurgical homogeneity, and surface integrity:
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Raw Material Selection and Inspection:
Virgin stainless steel billets or slabs are procured from certified suppliers with full chemical composition analysis and spectroscopic verification. Incoming materials undergo ultrasonic testing (UT) to detect internal defects such as inclusions, voids, or laminations.
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Hot Rolling and Annealing:
Billets are reheated to 1,150–1,250 °C and hot-rolled into semi-finished tube blanks. The rolled blanks are subsequently solution-annealed at 1,050–1,100 °C followed by controlled water or air quenching to achieve a fully austenitic, stress-free microstructure with uniform grain size (ASTM grain size 6–8).
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Piercing and Cold Drawing:
Semi-finished tubes are pierced to establish the initial bore, then cold-drawn through precision tungsten carbide or hardened steel dies to achieve final OD and wall thickness tolerances. Multiple drawing passes may be employed for tight tolerance requirements (±0.05 mm).
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Intermediate Annealing:
Between cold-drawing passes, tubes are annealed at 1,050 °C to relieve work-hardening, restore ductility, and prevent cracking. This step is repeated as necessary to achieve the final dimensions without exceeding the cumulative cold-work strain limit.
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Coil Winding (Helical Forming):
Finished straight tubes are fed through a precision coil-winding machine equipped with CNC-controlled forming rolls. The tube is helically wound onto a mandrel of the specified mean diameter, with the pitch controlled by the feed rate and rotation speed. The winding process is performed at ambient temperature, with the austenitic alloy's high ductility (elongation >40%) accommodating the plastic deformation without