Effect of a single deep longitudinal (SDL) dimple on turbulent fluid flow and thermal performance in circular tubes

In the field of turbulent heat transfer and fluid dynamics within circular tubes, this study investigates the effect of single-depth longitudinal (SDL) dimple geometry. The main research objective is to clarify how single-depth longitudinal dimple geometry (rectangular, triangular, and semicircular, of different sizes) affects heat transfer and fluid flow patterns under turbulent conditions (3000 < Reynolds number < 10,000) within circular tubes. The study evaluates the thermal efficiency and friction coefficients of proposed dimple configurations to analyze heat transfer rates and pressure losses. The results show that Single deep longitudinal dimples in circular tubes increase the Nu number by 22–43% over Reynolds numbers ranging from 3000 to 10,000, with semicircular Model B achieving peak overall performance factor (OPF) 1.712 (avg 1.32 at depth ratio 0.2). Although pumping losses increase with increasing dimple depth, an overall performance factor (OPF) greater than 1.2 confirms net thermal–hydraulic gains compared to smooth tubes. It is worth noting that pumping losses increase significantly with increasing depth ratios. These results enable the formulation of six equations derived from regression analysis. These equations establish relationships between the Nu number, friction factor, Reynolds number, Prandtl number, and depth ratio (e), aiming to simplify thermal performance predictions and improve system analyses in the context of heat transfer and fluid dynamics within circular tubes. This study highlights the significant impact of SDL dimple geometry on heat transfer and fluid flow, providing valuable insights for enhancing the efficiency of heat exchangers in engineering applications.