Thermo-Hydraulic Performance Optimization of Intrusion-Type Curved Fins in Tube-Bank Heat Exchangers Using Response Surface Methodology

Flow separation and wake formation around circular tubes are among the primary causes of pressure losses and limited heat transfer performance in tube-bank heat exchangers (TBHEs). In this study, the thermo-hydraulic performance of a staggered circular tube-bank heat exchanger enhanced with a novel Inward Curved Ring-Winglet (ICRW) configuration was numerically investigated. Unlike conventional external fins that primarily increase surface area, the proposed intrusion-type design modified the core flow by partially penetrating into the channel region, promoting longitudinal vortex formation while suppressing wake recirculation. A three-dimensional steady-state CFD framework was developed in ANSYS Fluent using the RNG k–ε turbulence model to analyze airflow and heat transfer characteristics. The effects of four geometric parameters, namely winglet length (L), winglet gap (G), inclination angle (θ), and channel height (H), together with the Reynolds number (Re), were systematically examined using Response Surface Methodology (RSM). A Central Composite Design–based RSM framework was employed to construct surrogate models and identify the optimal design by maximizing the thermo-hydraulic performance factor (TPF). The performance evaluation was based on the TPF, which accounts for both Colburn j-factor and friction factor. The investigated parameter ranges were L = 12.5–22.5 mm, G = 0.75–2.25 mm, θ = 3.75°–15°, H = 3.125–12.5 mm, and Re = 1100–11500. The RSM analysis identified an optimal configuration at L = 22.105 mm, G = 2.10 mm, θ = 5.12°, and H = 3.14 mm, for which the maximum TPF of 1.53 was achieved at Re = 11239. Compared to the baseline tube-bank configuration, the optimized ICRW design significantly enhances heat transfer while maintaining acceptable pressure losses. Flow visualization results indicate that the improvement is mainly attributed to intensified longitudinal vortex structures and effective disruption of thermal boundary layers. The results demonstrate that intrusion-type ICRW fins provide a compact and effective passive enhancement strategy for high-performance air-side TBHE applications.