Stainless Steel Coil Tube — Large Temperature Difference Chilled Water Cooling System Application
1. Product Overview
The Stainless Steel Coil Tube (盘管) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular component designed for integration into large temperature difference (LTD) chilled water cooling systems. This product is specifically optimized for use in fan coil unit serial radiator configurations connected to chilled water storage pools (蓄冷水池), representing a next-generation approach to energy-efficient building HVAC (Heating, Ventilation, and Air Conditioning) infrastructure.
Unlike conventional stainless steel coils operating under standard temperature differentials (ΔT = 5–7°C), this coil tube product is engineered to withstand and efficiently transfer thermal energy under large temperature difference conditions (ΔT ≥ 10–15°C), leveraging the thermal mass of chilled water pools to achieve significant energy savings in cooling loads.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade austenitic stainless steel, conforming to the following international standards:
- ASTM A213 / A269 — Seamless and welded stainless steel tubing
- EN 10216-5 — European specification for seamless tubes
- GB/T 12771 — Chinese national standard for stainless steel seamless tubes
2.2 Grade Options
- 304 (A2-D) — General-purpose grade with excellent corrosion resistance in non-chloride environments
- 316L (A2-D) — Enhanced chloride and pitting resistance for aggressive water treatment chemistries
- 321 (A1-D) — Stabilized grade suitable for elevated temperature zones near pool heat exchange interfaces
2.3 Key Physical & Thermal Properties
| Property | 304 Grade | 316L Grade | Unit |
|---|---|---|---|
| Thermal Conductivity (25°C) | 16.3 | 14.6 | W/(m·K) |
| Specific Heat Capacity | 500 | 500 | J/(kg·K) |
| Density | 8.00 | 8.03 | g/cm³ |
| Operating Temperature Range | -196 to +870 | °C | |
| Corrosion Resistance (ASTM G48) | Class 1A | Class 1B | — |
| Surface Roughness (Ra) | ≤ 0.8 | μm | |
2.4 Thermal Performance Under Large Temperature Difference
In the context of a chilled water pool-based cooling system, the coil tube experiences supply temperatures as low as 4–6°C with return temperatures reaching 18–22°C, creating a temperature differential of up to 16°C. The stainless steel material's stable thermal conductivity across this range ensures consistent heat transfer coefficient (U-value) without degradation, unlike polymer alternatives that suffer from thermal fatigue under cyclic ΔT exposure.
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Product Type | Coil Tube (盘管) for Fan Coil Unit Serial Radiator |
| Tube Outer Diameter (OD) | 6.35 mm / 9.53 mm / 12.70 mm (1/4" / 3/8" / 1/2") |
| Tube Wall Thickness | 0.5 mm – 1.2 mm (configurable) |
| Coil Diameter | 150 mm – 600 mm |
| Coil Length / Developed Length | 2.0 m – 12.0 m |
| Number of Turns | 8 – 60 turns |
| Fin Type (if finned) | Aluminum flat plate / V-type / L-type fins |
| Fin Density | 10 – 16 fins/inch |
| Maximum Working Pressure | 1.6 MPa (232 psi) |
| Hydrostatic Test Pressure | 2.4 MPa (348 psi) |
| Surface Finish | Bright annealed / Passivated / Electropolished |
| End Connection | Flared / Threaded / Welded (MIG/TIG) / Flanged |
| Maximum Flow Velocity | ≤ 2.5 m/s (chilled water side) |
| Applicable Chilled Water ΔT | 10°C – 16°C (large temperature difference) |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Inspection — Incoming stainless steel bar stock or seamless tube undergoes spectroscopic analysis (PMI) to verify alloy composition compliance with ASTM/EN standards.
- Tube Drawing & Forming — The base tube is cold-drawn to precise OD and wall thickness tolerances (±0.05 mm), followed by annealing at 1050°C to relieve residual stresses.
- Coil Winding (Coiling) — A CNC-controlled coiling machine forms the tube into the specified helical geometry. The winding process maintains constant pitch and avoids work-hardening that could compromise fatigue life.
- Fin Attachment (if applicable) — Aluminum fins are mechanically rolled or welded onto the stainless steel coil tube. The bimetallic bonding process ensures low thermal contact resistance (< 0.01 K·m²/W).
- Welding & Assembly — Header connections and inlet/outlet ports are TIG-welded (GTAW) with argon shielding gas. Welds undergo 100% visual inspection and spot radiographic testing (RT).
- Surface Treatment — Passivation treatment (per ASTM A967) using nitric acid or citric acid solution removes free iron contamination, forming a stable chromium oxide passive film (Cr₂O₃, thickness 2–5 nm).
- Pressure Testing — Each coil tube assembly undergoes hydrostatic pressure testing at 1.5× maximum working pressure for a minimum dwell time of 30 minutes, with zero leakage tolerance.
- Final Inspection & Packaging — Dimensional verification, surface quality audit, and protective packaging with moisture-absorbent desiccants prior to shipment.
4.2 Quality Control Milestones
- In-process dimensional checks at coiling stage (laser gauge)
- Post-fin attachment thermal resistance testing (sample basis)
- 100% hydrostatic test with documented pressure-time profile
- Final dimensional report (CofA — Certificate of Analysis)
5. System Application: Large Temperature Difference Chilled Water Cooling
5.1 System Architecture
The coil tube is designed for integration into a chilled water pool-based fan coil unit serial radiator large temperature difference cooling system (基于蓄冷水池的风机盘管串联散热器大温差供冷系统). The system architecture comprises:
- Chilled Water Pool (蓄冷水池) — A large-volume thermal storage reservoir maintained at 4–6°C, serving as the primary cold source
- Serial Radiator Configuration (串联散热器) — Multiple fan coil units connected in series, each containing the stainless steel coil tube as the primary heat exchange element
- Large Temperature Difference Circulation — Operating with ΔT ≥ 10°C between supply and return, reducing pumping energy by 60–70% compared to conventional ΔT = 5°C systems
- Variable Flow Control — Electronic expansion valves and modulating pumps adjust flow rates to match dynamic cooling loads
5.2 Performance Advantages
| Performance Metric | Conventional System (ΔT = 5°C) | LTD System (ΔT ≥ 10°C) | Improvement |
|---|---|---|---|
| Circulation Pump Power | Baseline | 30–40% | 60–70% reduction |
| Chilled Water Flow Rate | Baseline | 50% | 50% reduction |
| Pipe Diameter Required | Baseline | 30–40% smaller | Material savings |
| Overall System COP | Baseline | +15–25% | Higher efficiency |
5.3 Target Application Sectors
- Commercial Buildings — Office towers, shopping malls, and hotels with moderate-to-large cooling loads
- Industrial Facilities — Clean rooms, electronics manufacturing, and process cooling where stable temperature control is critical
- Healthcare Facilities — Hospitals and laboratories requiring high reliability and corrosion-resistant heat exchange components
- Data Centers — Server room cooling where energy efficiency (PUE reduction) is a primary design objective
- Renewable Energy Integration — Systems coupled with solar-assisted chillers or geothermal heat pumps utilizing thermal storage pools
6. Quality Certifications & Standards Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance |
| ASTM A213 / A269 | Material specification for tubing |
| EN 10216-5 | European seamless tube standard |
| GB/T 12771 | Chinese national standard for stainless steel tubes |
| ASME B31.5 | HVAC piping and piping components (if applicable) |
| NSF/ANSI 61 | Drinking water system components (potable water contact) |
7. Unique Selling Points
- Large ΔT Capability — Engineered specifically for large temperature difference applications (ΔT ≥ 10°C), enabling significant pump energy savings in chilled water pool cooling systems.
- Corrosion Resistance — Austenitic stainless steel construction ensures 20+ year service life in aggressive water chemistries, eliminating internal fouling and scale buildup that plague copper coil alternatives.
- Hygienic Surface — Bright-annealed and passivated surface with Ra ≤ 0.8 μm prevents microbial colonization and biofilm formation, critical for healthcare and food-grade applications.
- Thermal Stability — Maintains consistent thermal conductivity across the full operating temperature range (4°C to 22°C), ensuring predictable heat transfer performance cycle after cycle.
- Customizable Geometry — Modular coil dimensions (OD, wall thickness, coil diameter, developed length) allow system-level optimization for specific cooling loads and space constraints.
- Low Maintenance — Elimination of copper's susceptibility to dezincification and amine stress corrosion cracking (ASCC) reduces lifecycle maintenance costs by an estimated 40–50%.
Engineering Note: When integrating this coil tube into a chilled water pool-based large temperature difference system, it is recommended to maintain a minimum flow velocity of 0.5 m/s to prevent stratification within the pool and to ensure uniform temperature distribution across the serial radiator circuit. Anti-vibration mounts and flexible connectors should be specified at all rigid-to-flexible transitions to accommodate thermal expansion (α = 17.3 × 10⁻⁶ /K for 304 SS).