Stainless Steel Coil Tube for Cooling and Dehumidifying Systems

Product Overview

The stainless steel coil tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered heat exchange component specifically designed for cooling and dehumidifying applications within HVAC (Heating, Ventilation, and Air Conditioning) systems, refrigeration units, and industrial thermal management installations. This product category (Catalog No. 1310) represents a critical element in air-handling units (AHUs), chiller systems, and dehumidification equipment where efficient heat transfer and condensation management are paramount.

The coil tube is fabricated from high-grade stainless steel and formed into continuous helical or serpentine configurations to maximize surface area within a compact envelope. The design facilitates superior thermal performance, enabling effective sensible and latent heat transfer during cooling and dehumidification cycles. The product adheres to rigorous engineering standards and has been validated through comprehensive thermal calculation methodologies, including steady-state and transient-state heat transfer analyses.

Material and Properties

The coil tube is constructed from premium austenitic stainless steel, selected for its exceptional combination of corrosion resistance, thermal conductivity, and mechanical durability. Key material characteristics include:

• Primary Alloy Grade: SUS304 (ASTM A269 TP304) or SUS316L (ASTM A269 TP316L), depending on the specific corrosion environment requirements.
• Corrosion Resistance: Superior resistance to condensate corrosion, acidic water attack, and chlorinated environments—critical in dehumidification applications where persistent moisture contact is expected.
• Thermal Conductivity: Approximately 16.3 W/(m·K) for SUS304 grade, ensuring efficient heat exchange between the refrigerant medium and the ambient air stream.
• Operating Temperature Range: -196°C to +870°C (SUS304), providing reliability across extreme thermal cycling conditions.
• Mechanical Strength: Yield strength of ≥205 MPa (0.2% offset), with ultimate tensile strength of ≥515 MPa, ensuring structural integrity under pressure differentials and vibration loads.
• Surface Finish: Available in polished (Ra ≤ 0.8 μm), brushed, or passivated finishes to minimize fouling and facilitate condensate drainage.

Technical Specifications

Parameter	Specification	Standard / Reference
Outer Diameter (OD)	3.0 mm – 12.7 mm (standard); custom diameters available	ISO 285
Wall Thickness	0.3 mm – 1.5 mm (typical range)	ASTM A269
Coil Pitch (Helical)	5.0 mm – 30.0 mm (configurable per thermal design)	Manufacturer Specification
Serpentine Row Spacing	15 mm – 50 mm (adjustable for airflow velocity optimization)	ASHRAE Handbook — HVAC Systems
Tube Length per Coil	0.5 m – 15.0 m (custom fabrication)	—
Maximum Working Pressure	2.5 MPa (at 25°C)	ASME B31.5
Hydrostatic Test Pressure	3.75 MPa (1.5× working pressure)	ASME B31.5
Refrigerant Compatibility	R-22, R-134a, R-407C, R-410A, R-32, R-1234yf, Water/Glycol mixtures	ASHRAE Standard 34
Surface Treatment	Passivation, hydrophilic coating (optional for enhanced condensate shedding)	—
Fin Material (if applicable)	Aluminum (Al 3003) or stainless steel micro-fins	—
Coil Configuration	Serpentine, helical, double-row, multi-row, or custom geometry	—
Connection Type	Flared, threaded (NPT/BSP), brazed, or welding-ready ends	ISO 228 / ASME B1.20.1
Weight (per meter)	Varies by OD and wall thickness; typically 0.05 – 0.35 kg/m	—

Thermal Performance and Calculation Methodology

The thermal design and validation of the coil tube are based on rigorous engineering calculations consistent with established methodologies for cooling and dehumidifying coil performance. The key thermal parameters are determined through the following analytical framework:

Heat Transfer Calculations

• Sensible Heat Load (Q_s): Calculated as Q_s = m_air × cp × ΔT_db, where m_air is the air mass flow rate, cp is the specific heat capacity of air, and ΔT_db is the dry-bulb temperature difference across the coil.
• Latent Heat Load (Q_l): Determined as Q_l = m_air × h_fg × ΔW, where h_fg is the latent heat of vaporization and ΔW is the change in humidity ratio across the coil.
• Total Heat Load (Q_t): Q_t = Q_s + Q_l, representing the combined thermal capacity of the coil assembly.
• Overall Heat Transfer Coefficient (U): Computed considering convective coefficients on both the air side (h_air) and the refrigerant side (h_ref), corrected for fin efficiency (η_f) and fouling factors (R_f).

Performance Metrics

• Effective Sensible Heat Ratio (SHR): SHR = Q_s / Q_t, typically ranging from 0.50 to 0.75 for dehumidifying coils, ensuring balanced sensible and latent cooling.
• Approach Temperature: Minimum temperature difference between the leaving air and the mean refrigerant temperature, typically ≤ 3°C for optimized coil designs.
• Condensate Rate: Calculated based on the enthalpy method, with design targets of 0.5 – 3.0 L/h per unit of cooling capacity depending on operating conditions.
• Pressure Drop (Air Side): Engineered to remain within 25 – 150 Pa, ensuring compatibility with standard AHU fan systems.

Manufacturing Process

The coil tube undergoes a multi-stage precision manufacturing process to ensure dimensional accuracy, thermal integrity, and long-term reliability:

1. Material Selection and Inspection: Stainless steel seamless or welded tube stock is procured in compliance with ASTM A269 or equivalent standards. Incoming material undergoes spectroscopic analysis (PMI — Positive Material Identification), visual inspection, and dimensional verification.
2. Cutting and End Preparation: Tubes are cut to specified lengths using precision saws or laser cutting, followed by deburring and end-finishing to ensure clean, burr-free connection surfaces.
3. Forming and Coiling: Tubes are cold-formed into the required serpentine or helical geometry using CNC-controlled bending machinery. The forming process maintains wall thickness uniformity (tolerance ±10%) and avoids work hardening that could compromise fatigue life.
4. Heat Treatment (if required): For SUS316L grades, solution annealing may be applied at 1050°C followed by rapid quenching to restore full austenitic structure and maximize corrosion resistance.
5. Fin Attachment (if finned coil): Aluminum or stainless steel fins are mechanically or brazed onto the tube surface at precise spacing intervals to enhance the effective heat transfer area by 3–8×.
6. Surface Treatment: Passivation treatment is applied using nitric acid or citric acid solutions to remove free iron and establish a protective chromium oxide layer. Optional hydrophilic coatings may be applied to promote rapid condensate shedding and reduce microbial growth.
7. Pressure Testing: Each coil assembly undergoes 100% hydrostatic pressure testing at 1.5× the maximum working pressure, held for a minimum of 30 minutes with zero leakage tolerance.
8. Final Inspection and Packaging: Completed coils are inspected for dimensional accuracy, surface quality, and weld integrity (visual and, where applicable, dye penetrant testing). Products are packaged in protective foam and moisture-barrier wrapping for shipment.

Applications

The stainless steel coil tube is engineered for demanding cooling and dehumidification applications where material integrity, thermal efficiency, and long service life are critical:

• HVAC Systems: Integration into air-handling units (AHUs), rooftop units (RTUs), and packaged terminal units (PTUs) for commercial, industrial, and institutional buildings.
• Dehumidification Equipment: Standalone dehumidifiers, process air drying systems, and moisture-sensitive manufacturing environments (pharmaceutical cleanrooms, electronics fabrication, food processing).
• Refrigeration Systems: Evaporator coils in commercial refrigeration, cold storage facilities, and process refrigeration applications.
• Heat Pump Systems: Indoor evaporator coils in air-to-air and air-to-water heat pump units for both heating and cooling modes.
• Industrial Process Cooling: Precision temperature and humidity control in data centers, laboratories, and specialized manufacturing processes.
• Chiller Systems: Secondary-side coil assemblies in chiller plant systems for large-scale building cooling.

Quality Certifications and Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring product conformity with international standards:

• ISO 9001:2015 — Quality Management System certification, demonstrating systematic process control from raw material procurement through final delivery.
• ISO 14001:2015 — Environmental Management System certification, reflecting commitment to sustainable manufacturing practices and waste minimization.
• ASTM A269 — Compliance with the standard specification for seamless and welded austenitic stainless steel tubing for general applications.
• ASME B31.5 — Pressure piping code compliance for refrigeration and air-conditioning systems.
• EN 10216-5 — European standard for welded stainless steel tubes for heat exchangers and boilers.
• GB/T 12771 — Chinese national standard for stainless steel seamless tubes for heat exchangers.
• ASHRAE Handbook — HVAC Systems — Design methodology alignment for thermal performance calculations and coil selection.
• Material Traceability: Full mill certification (EN 10204 Type 3.1) provided with each batch, including chemical composition, mechanical properties, and heat treatment records.

Unique Selling Points

• Enhanced Durability in Wet Environments: The austenitic stainless steel construction provides unparalleled resistance to condensate-induced corrosion, significantly extending service life compared to copper or carbon steel alternatives in dehumidifying applications.
• Precision Thermal Engineering: Each coil geometry is validated through detailed thermal calculation methodologies, ensuring optimal balance between sensible and latent heat removal for efficient dehumidification performance.
• Customizable Geometry: Flexible manufacturing capability allows for bespoke coil configurations—varying OD, wall thickness, pitch, row count, and total length—to match specific system design requirements.
• Low Fouling Surface: Smooth, passivated surfaces minimize scale and biofilm accumulation, reducing maintenance frequency and preserving heat transfer efficiency over the product lifecycle.
• Hygienic Design: Suitable for food-grade and pharmaceutical applications where condensate cleanliness is a regulatory requirement.
• Comprehensive Quality Assurance: 100% pressure testing, full material traceability, and multi-standard compliance provide confidence in product reliability for safety-critical installations.

Note: All specifications are subject to engineering review based on the specific application conditions, refrigerant type, operating pressures, and ambient parameters. Wenzhou Jixing Metal Materials Co., Ltd provides technical consultation and thermal calculation support for custom coil designs to ensure optimal system performance.