Numerical optimization by deep single selective investigation and experimental validation for star-fin inserts in absorber tubes

Limited thermal efficiency remains a persistent challenge in the design of modern heat exchangers employing absorber tubes. This study addresses this limitation by integrating geometric fin optimization with nanofluid enhancement to maximize the thermal-hydraulic performance factor (THPF). A novel star-finned copper absorber tube was designed for turbulent flow conditions. The optimization was carried out using the Deep Single-Selective Investigation (DSSI) methodology, considering five key geometric parameters: fin edge number (2-5), fin diameter (14-15.5 mm), fin thickness (2-3.5 mm), number of fins per rod (4-8), and angular spacing (0-40°). The analysis was conducted under hydraulic and geometric constraints, with Reynolds numbers ranging from 6000 to 15,000 and a fixed absorber tube diameter of 19.10 mm. The optimal configuration consisted of a five-edge fin with a 15.5 mm diameter, six fins per rod, a thickness of 3 mm, and an angular spacing of 30°. Numerical results showed THPF values of 1.856 with distilled water and 2.100 with the 0.2% Al 2 O 3 nanofluid, demonstrating the enhanced THPF compared with a smooth tube baseline. Experimental validation yielded THPF values of 1.834 with distilled water and 2.004 with the nanofluid. CFD predictions matched experiments (R 2 = 0.9982, RMSE = 2.42), confirming the robustness of the framework and supporting the applicability of the proposed design for advanced thermal systems.