Vertical Spiral Stainless Steel Coiled Tube — Descending Film Absorber Grade
Product Overview
The Vertical Spiral Stainless Steel Coiled Tube (Model No. 829) is a precision-engineered coil tube product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for application in vertical spiral coiled tube descending film absorbers, where it serves as the core heat and mass transfer element. The coiled tube is wound in a helical configuration to maximize surface area-to-volume ratio, facilitating efficient absorption of refrigerant vapor into a liquid absorbent solution flowing as a thin film along the outer surface of the coil.
Unlike conventional straight-tube heat exchangers, the spiral coil geometry promotes natural convection enhancement and uniform film distribution, resulting in superior thermodynamic performance. This product line has been validated through rigorous design and experimental research, with performance data confirming significant improvements in absorption efficiency compared to flat-tube alternatives.
Material & Properties
The coiled tubes are fabricated from high-grade austenitic stainless steel, selected for its exceptional corrosion resistance, thermal conductivity, and mechanical integrity under demanding operating conditions.
- Primary Material Grades: SUS304 (ASTM 304), SUS316L (ASTM 316L), and SUS321 (ASTM 321) austenitic stainless steel
- Chemical Composition (SUS316L): Carbon ≤0.03%, Chromium 16.0–18.0%, Nickel 10.0–14.0%, Molybdenum 2.0–3.0%, Silicon ≤1.0%, Manganese ≤2.0%
- Mechanical Properties: Tensile strength ≥520 MPa (minimum), Yield strength ≥205 MPa, Elongation ≥40%
- Thermal Conductivity: 14.6–16.3 W/(m·K) at 20°C
- Corrosion Resistance: Excellent resistance to chloride-induced pitting, intergranular corrosion, and general atmospheric corrosion
- Operating Temperature Range: −196°C to +870°C (SUS304/316L)
Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Outer Diameter (OD) | 6.0 / 8.0 / 10.0 / 12.0 / 14.0 / 16.0 | mm |
| Wall Thickness | 0.5 / 0.8 / 1.0 / 1.2 / 1.5 | mm |
| Coil Diameter (CD) | 50 – 500 | mm |
| Coil Pitch (Center-to-Center) | 10 – 50 | mm |
| Tube Length per Coil | 1 – 50 | m |
| Surface Finish | 2B / BA / Electropolished (Ra ≤0.4 μm) | — |
| End Form | Plain / Flared / Flanged / Threaded | — |
| Pressure Rating | Up to 4.0 | MPa |
| Winding Direction | Left-hand / Right-hand helical | — |
| Applicable Standards | GB/T 14976, ASTM A213, EN 10216-5, JIS G3459 | — |
Manufacturing Process
The production of vertical spiral coiled tubes involves a multi-stage precision manufacturing sequence to ensure dimensional accuracy, metallurgical integrity, and functional performance:
- Raw Material Selection & Inspection: Cold-rolled stainless steel tubing is sourced from certified mills and subjected to incoming quality control including chemical analysis, dimensional verification, and non-destructive testing (NDT).
- Cold Drawing & Sizing: Tubes are cold-drawn to precise outer diameter and wall thickness tolerances (±0.05 mm) using hardened tooling to maintain surface finish quality.
- Heat Treatment (Solution Annealing): Tubes undergo solution annealing at 1010–1150°C followed by rapid water quenching to achieve a fully austenitic microstructure, ensuring maximum corrosion resistance and ductility.
- Precision Coil Winding: Tubes are wound onto precision mandrels using CNC-controlled coiling machines. The winding parameters (pitch, coil diameter, number of turns) are programmed to exact specifications. The winding process is performed at controlled ambient temperature to prevent residual stress accumulation.
- Stress Relief Annealing: Post-winding stress relief is conducted at 400–500°C (for SUS304/316L) to eliminate residual stresses induced during the cold winding process, preventing spring-back and dimensional drift.
- End Processing: Tube ends are machined, flared, or fitted with threaded/flanged connectors according to customer specifications.
- Surface Treatment: Optional electropolishing or passivation treatment is applied to achieve ultra-low surface roughness (Ra ≤0.4 μm), critical for promoting uniform descending film formation on the tube outer surface.
- Final Quality Assurance: Each coil undergoes hydrostatic pressure testing, dimensional inspection (OD, wall thickness, coil diameter, pitch), visual examination, and optional eddy current testing for wall thickness verification.
Applications
The vertical spiral coiled tube descending film absorber is a specialized heat exchanger configuration with the following primary applications:
- Ammonia-Water Absorption Refrigeration Systems: Serves as the absorption heat exchanger where ammonia vapor is absorbed by water-rich solution, with heat removal through the coiled tube carrying coolant.
- Lithium Bromide-Water Absorption Chillers: Utilized in large-scale industrial absorption chillers for district cooling and process cooling applications.
- Heat Pump Systems: Integrated into absorption heat pumps for waste heat recovery and high-grade heat generation.
- Process Industry: Applied in chemical processing where efficient gas absorption and heat exchange are required simultaneously.
- Research & Development: Used as experimental apparatus for studying mass transfer and heat transfer characteristics in descending film absorption processes.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems to ensure product reliability and international compliance:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- EN 10204 3.1 — Material Test Certificates (MTC) provided with each batch
- CE Marking — Compliance with European machinery and pressure equipment directives
- ASME — American Society of Mechanical Engineers standards compliance for pressure-containing components
- NB (National Supervision Bureau) — Chinese pressure vessel and piping component manufacturing license
- Mill Test Reports — Full chemical composition, mechanical properties, and heat number traceability
- Non-Destructive Testing (NDT): Eddy current, ultrasonic, and dye penetrant testing available upon request
Unique Selling Points
1. Superior Heat & Mass Transfer Performance
The helical coil geometry creates natural secondary flow patterns (Dean vortices) that continuously disrupt the thermal boundary layer, enhancing heat transfer coefficients by 20–40% compared to equivalent straight-tube configurations. This translates to more compact absorber designs and reduced capital expenditure.
2. Uniform Descending Film Distribution
The precise coil winding pitch ensures consistent spacing between adjacent turns, promoting uniform distribution of the absorbent solution film. This uniformity minimizes dry patches and flooding, maximizing the effective absorption area and overall system COP (Coefficient of Performance).
3. Exceptional Durability & Corrosion Resistance
Stainless steel construction with optional molybdenum-enhanced grades (SUS316L) provides outstanding resistance to the corrosive effects of ammonia-water and lithium bromide solutions, ensuring extended service life exceeding 20 years under normal operating conditions.
4. Precision Manufacturing & Customization
CNC-controlled winding ensures dimensional accuracy within ±0.5 mm tolerance, enabling seamless integration into modular absorber designs. Custom configurations (coil diameter, pitch, number of turns, end fittings) are available to meet specific engineering requirements.
5. Research-Validated Design
The product design is supported by comprehensive experimental research on vertical spiral coiled tube descending film absorbers, with validated performance correlations for heat and mass transfer coefficients, pressure drop, and film flow characteristics. This provides engineers with reliable design data for system optimization.
6. Energy Efficiency Contribution
By enabling high-efficiency absorption refrigeration systems that operate on waste heat or low-grade thermal energy, these coiled tubes contribute to significant energy savings and reduced greenhouse gas emissions compared to vapor-compression alternatives.