Stainless Steel Coil Tube — Cross-Sectional Shape Optimization for Evaporative Condenser Heat Transfer

1. Product Overview

The Stainless Steel Coil Tube (Product No. 555) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd., designed specifically for use in evaporative condenser systems and other high-efficiency heat exchange applications. This product represents the culmination of extensive numerical simulation research focused on the relationship between coil cross-sectional geometry and thermal performance.

Through rigorous computational fluid dynamics (CFD) and conjugate heat transfer (CHT) analysis, Wenzhou Jixing has optimized the cross-sectional profiles of its coil tubes to maximize heat transfer coefficients while minimizing pressure drop and pumping power requirements. The product line encompasses circular, elliptical, oval, rectangular, and custom-profiled coil tubes, each validated through both simulation and experimental verification.

The coil tube serves as the primary heat exchange surface in evaporative condensers, where refrigerant or process fluid flows through the internal channels while water film and air flow over the external surface. The geometric characteristics of the coil cross-section directly influence the turbulence intensity, boundary layer development, and ultimately the overall thermal efficiency of the system.

2. Material & Properties

2.1 Base Materials

2.2 Physical Properties (Typical for SUS304)

Property Value Unit Standard Reference
Density (ρ) 7.93 g/cm³ ASTM A240
Thermal Conductivity (λ) at 20°C 16.3 W/(m·K) ASTM A240
Specific Heat Capacity (cₚ) at 20°C 502 J/(kg·K) ASTM A240
Thermal Expansion Coefficient (α) 20–100°C 17.3 × 10⁻⁶ 1/K ASTM A240
Yield Strength (σ₀.₂) Annealed ≥205 MPa ASTM A240
Tensile Strength (σᵤ) Annealed 515–720 MPa ASTM A240
Elongation (A₅₀mm) ≥40 % ASTM A240

2.3 Chemical Composition (SUS304, wt%)

Element C Si Mn P S Cr Ni N
Maximum/Range ≤0.08 ≤1.00 ≤2.00 ≤0.045 ≤0.030 18.0–20.0 8.0–10.5 ≤0.10

3. Specifications

3.1 Cross-Sectional Geometries

Parameter Specification Tolerance Standard
Outer Dimensions (Circular) Φ6.0 – Φ32.0 mm ±0.1 mm ASTM A269 / GB/T 12771
Outer Dimensions (Oval/Elliptical) 6×10 mm – 25×50 mm ±0.15 mm ASTM A269 / EN 10217
Outer Dimensions (Rectangular) 6×6 mm – 30×30 mm ±0.15 mm ASTM A269 / EN 10217
Wall Thickness 0.3 – 3.0 mm ±10% ASTM A269
Coil Winding Diameter 50 – 500 mm ±2 mm Custom / Project Spec.
Coil Length (per roll) Up to 500 m — —
Surface Finish (Internal) Ra ≤ 0.8 μm (standard); Ra ≤ 0.4 μm (polished) — ASTM A270
Surface Finish (External) 2B / No.4 / Mirror (Ra ≤ 0.2 μm) — ASTM A480
Operating Temperature Range −196°C to +870°C (SUS304) — —
Maximum Operating Pressure ≤ 4.0 MPa (typical); up to 10.0 MPa (heavy wall) — ASME B31.3
Hydrostatic Test Pressure 1.5 × Maximum Operating Pressure — ASTM A269

3.2 Heat Transfer Performance Characteristics

Cross-Section Shape Heat Transfer Coefficient Enhancement Pressure Drop Ratio Optimal Reynolds Number Range
Circular (Baseline) 1.00 (Reference) 1.00 (Reference) Re > 2300 (Turbulent)
Oval (Aspect Ratio 2:1) 1.15 – 1.35 1.10 – 1.25 Re > 1800 (Turbulent)
Elliptical (Aspect Ratio 3:1) 1.25 – 1.50 1.20 – 1.40 Re > 1500 (Turbulent)
Rectangular 1.20 – 1.45 1.15 – 1.35 Re > 1600 (Turbulent)
Custom Profiled (Wavy/Ribbed) 1.40 – 1.80 1.30 – 1.60 Re > 1200 (Transitional/Turbulent)

4. Manufacturing Process

4.1 Process Flow

  1. Raw Material Procurement & Inspection: Stainless steel strip or round bar sourced from certified mills, subjected to spectroscopic analysis (OES), mechanical testing, and dimensional verification per ASTM A240 / A269.
  2. Surface Preparation: Acid pickling and passivation treatment to remove oxide scale and ensure a chromium-rich passive film on the surface.
  3. Forming & Coiling:
    • Circular coils: Seamless tube drawing followed by precision coiling using CNC-controlled winding machines.
    • Non-circular coils: Cold-rolled flat coil or drawn tube with cross-sectional forming via multi-die progressive tooling.
  4. Heat Treatment (if required): Solution annealing at 1050–1150°C followed by controlled cooling (air or water quench) to restore full austenitic microstructure and maximize corrosion resistance.
  5. Surface Finishing: Mechanical polishing, electropolishing, or passivation to achieve specified surface roughness (Ra) values for optimal heat transfer and corrosion performance.
  6. Dimensional Inspection: Coordinate Measuring Machine (CMM) inspection, ultrasonic wall thickness measurement, and optical profile analysis of cross-sections.
  7. Pressure Testing: Hydrostatic or pneumatic leak testing at 1.5× working pressure with holding time of minimum 30 seconds per coil section.
  8. End Processing: Cutting, deburring, end polishing, and protective cap installation.
  9. Packaging & Dispatch: Protective wrapping, moisture barrier packaging, and labeling with material certificates and traceability codes.

4.2 Numerical Simulation-Driven Optimization

Wenzhou Jixing Metal Materials employs advanced computational fluid dynamics (CFD) modeling using software platforms including ANSYS Fluent, COMSOL Multiphysics, and OpenFOAM to simulate heat transfer performance across various coil cross-sectional geometries. The simulation methodology includes:

5. Applications

5.1 Primary Applications

5.2 System Integration Parameters

System Parameter Typical Range Notes
Refrigerant Flow Velocity 0.5 – 3.0 m/s Optimized for minimum pressure drop
Water Film Flow Rate 100 – 300 L/(m²·h) External evaporative cooling
Air Velocity (Cross-flow) 1.5 – 3.5 m/s Forced draft configuration
Overall Heat Transfer Coefficient (U) 800 – 2,500 W/(m²·K) Depends on geometry and operating conditions
Approach Temperature 3 – 8 K Condensing temperature minus ambient wet-bulb

6. Quality Certifications & Standards

6.1 Material Certifications

6.2 System & Manufacturing Certifications