Stainless Steel Coil Tube (Coiltube) for Fan Coil Unit Heat Exchangers

Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.  |  Product Code: 1283  |  Category: Technical Literature & Engineering Reference

1. Product Overview

The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubing product specifically designed for integration into Fan Coil Unit (FCU) heat exchangers within Fan Coil Plus Fresh Air Air Conditioning Systems. These coil tubes serve as the primary heat transfer elements in evaporative and condensing coils, facilitating efficient thermal exchange between the refrigerant and the airstream in commercial and residential HVAC applications.

The product is developed in accordance with the ε-NTU (Effectiveness-Number of Transfer Units) Method of heat exchanger analysis, ensuring that each coil tube geometry is optimized for maximum thermal effectiveness (ε) under specified operating conditions. This design philosophy enables systematic comparison and selection of coil tube configurations to achieve superior performance in diverse system architectures.

2. Material Composition & Physical Properties

2.1 Base Material

The Coiltube is fabricated from high-grade Austenitic Stainless Steel, conforming to recognized international standards. The primary alloy grades include:

2.2 Key Physical Properties

Property Grade 304 Grade 316 Grade 316L Test Standard
Density (kg/m³) 8,000 8,000 8,000 ASTM A270
Thermal Conductivity (W/m·K) @ 300K 16.3 14.6 14.6 ASTM E153
Specific Heat (J/kg·K) @ 300K 500 500 500 ASTM E1225
Tensile Strength (MPa) ≥ 520 ≥ 515 ≥ 485 ASTM A270
Yield Strength (MPa) ≥ 205 ≥ 205 ≥ 170 ASTM A270
Elongation (%) ≥ 40 ≥ 40 ≥ 45 ASTM A270
Corrosion Potential (mV vs. SCE) −250 ~ −100 −200 ~ −50 −200 ~ −50 ASTM G102
Maximum Service Temperature (°C) 870 870 870 —

2.3 Chemical Composition (Typical, wt%)

Element Grade 304 Grade 316 / 316L
Carbon (C) ≤ 0.08 ≤ 0.03 (316L) / ≤ 0.08 (316)
Chromium (Cr) 18.0 – 20.0 16.0 – 18.0
Nickel (Ni) 8.0 – 10.5 10.0 – 14.0
Molybdenum (Mo) — 2.0 – 3.0
Iron (Fe) Balance Balance

3. Technical Specifications

3.1 Dimensional Parameters

Parameter Specification Tolerance Standard Reference
Outer Diameter (OD) 6.35 mm (¼"), 9.53 mm (⅜"), 12.7 mm (½") ± 0.05 mm ASTM A270 / EN 10217
Wall Thickness 0.50 mm – 1.20 mm ± 10% ASTM A270
Tube Length per Coil 2,000 mm – 12,000 mm (customizable) ± 50 mm Per customer drawing
Coil Diameter (Bundle OD) 300 mm – 1,200 mm ± 3 mm ASHRAE 15
Coil Height 150 mm – 600 mm ± 2 mm Per customer drawing
Tube Pitch (Vertical) 16 mm – 25 mm ± 0.5 mm ASHRAE Handbook
Tube Pitch (Horizontal) 16 mm – 25 mm ± 0.5 mm ASHRAE Handbook
Surface Finish Bright Annealed (BA) or Polished Ra ≤ 0.8 μm ASTM A478
End Condition Plain, Beveled, or Flanged ± 0.5 mm Per customer drawing

3.2 Thermal Performance Parameters (ε-NTU Basis)

Operating Condition Effectiveness (ε) NTU (Number of Transfer Units) Heat Transfer Coefficient (W/m²·K)
Cooling Mode (Dry) 0.75 – 0.88 2.5 – 4.0 60 – 120
Cooling Mode (Wet) 0.70 – 0.85 2.2 – 3.8 45 – 90
Heating Mode 0.80 – 0.92 3.0 – 4.5 80 – 150
Refrigerant Side (R410A) — — 2,000 – 4,500
Air Side (1.5 – 3.0 m/s) — — 25 – 60

3.3 Pressure & Flow Specifications

Parameter Specification
Design Pressure (Refrigerant Side) ≤ 3.5 MPa (R410A)
Design Pressure (Water Side) ≤ 1.6 MPa (Chilled/Hot Water)
Hydrostatic Test Pressure 1.5 × Design Pressure
Refrigerant Flow Rate 0.5 – 15.0 kg/h (per coil)
Water Flow Rate 0.2 – 5.0 L/min (per coil)
Pressure Drop (Air Side) 50 – 250 Pa
Pressure Drop (Refrigerant Side) ≤ 0.35 MPa

4. Manufacturing Process

The production of the stainless steel Coiltube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and thermal performance:

  1. Raw Material Procurement & Inspection: Stainless steel strip or seamless tubing is sourced from certified mills (e.g., Outokumpu, Sandvik, POSCO). Each batch undergoes spectroscopic analysis per ASTM E415 to verify chemical composition, along with mechanical testing per ASTM A370.
  2. Precision Forming & Bending: Tubes are cold-formed into coil configurations using CNC-controlled bending machinery. Bending radii are maintained at ≥ 3× tube OD to prevent ovalization and work hardening. Tolerance on coil geometry is controlled to ± 0.5 mm.
  3. Tube Fin Attachment: High-performance aluminum fins (0.10 – 0.15 mm thickness, 2.0 – 3.0 mm pitch) are mechanically bonded to the stainless steel tubes using either:
    • Stress Corrosion Resistant (SCR) Fin Coating to mitigate galvanic corrosion between dissimilar metals, or
    • Double-Side Coated (DSC) Aluminum Fins with a protective chromium-based surface treatment.
  4. Tin Welding / Brazing: Header connections are brazed using silver-based brazing alloy (Ag-Cu, Ag 5%) to ensure corrosion-resistant joints. Brazing is performed in a nitrogen-protected atmosphere to prevent oxidation.
  5. Pressure Testing: Each coil assembly undergoes a hydrostatic pressure test at 1.5× design pressure for a minimum of 15 minutes, with zero leakage tolerance. Electronic leak detection is performed for refrigerant-side integrity.
  6. Performance Testing & ε-NTU Verification: Selected samples are tested in a calibrated wind tunnel facility to measure actual thermal effectiveness (ε), NTU values, and heat transfer coefficients under standardized conditions per ASHRAE Standard 40 and ANSI/ASHRAE Standard 34.
  7. Final Inspection & Packaging: Coils are inspected for surface defects, dimensional accuracy, and protective coating integrity. Each unit is individually wrapped in moisture-barrier packaging with desiccant and serialized for traceability.

5. Applications

The stainless steel Coiltube from Wenzhou Jixing Metal Materials Co., Ltd. is engineered for the following primary application domains:

5.1 Commercial HVAC Systems