Stainless Steel Coil Tube for Fan Coil Unit Applications

Product Overview

The Stainless Steel Coil Tube (产品编号: 1052) is a precision-engineered coiled tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for use in Fan Coil Units (FCU) and similar HVAC (Heating, Ventilation, and Air Conditioning) systems. The coil tube serves as a critical heat exchange element, facilitating efficient thermal transfer between the circulating fluid medium and the ambient air stream within the fan coil assembly.

This product line addresses a key engineering challenge identified in the technical literature: the determination of inlet water temperature during dry operating conditions of fan coil units. The coil tube design ensures optimal thermal performance across both wet and dry operational modes, maintaining consistent heat transfer coefficients even when the system transitions between latent and sensible cooling/heating regimes.

Material & Properties

The coil tube is fabricated from high-grade austenitic stainless steel, selected for its superior corrosion resistance, thermal conductivity, and long-term structural integrity under cyclic thermal loading conditions.

Specifications

Parameter Specification Standard / Reference
Product Code 1052 Wenzhou Jixing Internal Catalog
Tube Outer Diameter (OD) 6.35 mm / 9.52 mm / 12.7 mm / Custom ASTM A213 / GB/T 12771
Tube Wall Thickness 0.5 mm – 1.5 mm ±10% tolerance
Coil Pitch (Center-to-Center) 15 mm – 40 mm (configurable) Engineered for airflow optimization
Coil Row Depth 2-row / 4-row / 6-row configurations ASHRAE Standard 90.1
Coil Length 200 mm – 1200 mm (standard range) Custom lengths available
Pressure Rating ≤ 1.6 MPa (standard); ≤ 2.5 MPa (reinforced) GB/T 15386 / ASME B31.5
Fluid Medium Water, Glycol-Water Mixture (up to 50% ethylene glycol) ASHRAE 90.1
Dry Operating Inlet Water Temperature ≥ 18°C (recommended minimum to prevent condensation) ASHRAE Handbook – HVAC Systems
Heat Transfer Efficiency U-value: 60 – 90 W/(m²·K) (air-side / water-side) ANSI/ASHRAE 40.1
End Connections Flanged / Threaded / Welded / Brazed ASME B31.5
Fin Configuration (if finned) Aluminum corrugated fins, 12–16 FPI Customizable

Manufacturing Process

The production of the stainless steel coil tube follows a rigorous, multi-stage manufacturing protocol to ensure dimensional accuracy, surface quality, and mechanical reliability:

  1. Material Selection & Incoming Inspection: Certified stainless steel wire rod or flat stock is procured from approved suppliers. Each batch undergoes spectroscopic analysis (OES) and mechanical testing to verify chemical composition and tensile properties conform to ASTM A213 or GB/T 12771 requirements.
  2. Pipe Forming: Raw stock is cold-drawn or cold-rolled into the specified tube geometry. Seamless tube production eliminates weld seams that could serve as corrosion initiation sites or flow disruption points.
  3. Coil Winding & Forming: Precision CNC coil winding machines form the tube into the designated spiral or serpentine configuration. The winding parameters (pitch, row count, tube OD) are calibrated to optimize the air-side heat transfer surface area while maintaining acceptable pressure drop across the coil.
  4. Welding & Brazing: Header connections and end fittings are joined using TIG (Tungsten Inert Gas) welding or vacuum brazing under controlled nitrogen or argon atmosphere to prevent oxidation of the internal tube surfaces.
  5. Fin Attachment (if applicable): Aluminum fins are mechanically bonded to the tube surfaces using a fin-insertion process, creating intimate metal-to-metal contact for maximum thermal conductivity between the tube and fin array.
  6. Heat Treatment: Post-weld annealing at controlled temperatures relieves residual stresses introduced during forming and welding, restoring the full mechanical properties of the austenitic microstructure.
  7. Surface Treatment & Cleaning: Internal and external surfaces are passivated using nitric acid or citric acid solutions to remove mill scale and form a protective chromium oxide layer. Final cleaning ensures the coil is free of particulate contamination prior to packaging.
  8. Pressure Testing & Quality Control: Each finished coil undergoes hydrostatic pressure testing at 1.5× the maximum working pressure. Non-destructive testing (NDT) methods including dye penetrant inspection and ultrasonic testing verify weld integrity and wall thickness uniformity.

Applications

The stainless steel coil tube is engineered for deployment in a wide range of thermal management systems:

Dry Operating Condition — Technical Consideration

A critical design parameter for fan coil unit coil tubes is the determination of the minimum inlet water temperature during dry operation. When the coil surface temperature falls below the dew point of the incoming air, condensation occurs, transitioning the system from dry (sensible-only) to wet (sensible + latent) operation. This transition has significant implications:

  • Increased total cooling capacity but reduced sensible heat ratio (SHR)
  • Introduction of condensate drainage requirements
  • Potential for microbial growth on wet coil surfaces
  • Increased fan static pressure due to condensate film on fins

Wenzhou Jixing Metal Materials Co., Ltd. provides engineering guidance and custom coil configurations to ensure that the inlet water temperature remains above the critical dew point threshold during dry operation, typically requiring a minimum supply water temperature of 18°C or higher, depending on the ambient air dew point conditions.

Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and certifications to ensure product reliability and international market compliance:

Unique Selling Points