Hydrothermal performance of turbulent flow in tubes with spherical dimples

Engineers increasingly utilize dimpled tubes in thermal systems to enhance performance, with spherical dimples demonstrating the most significant impact. Simple and accurate correlations are essential for efficiently assessing the performance of newly designed or improved equipment. Extensive research has been conducted on spherical dimples; however, no study has comprehensively examined the combined effects of geometric parameters such as dimple diameter, dimple pitch, and dimple stars. This study uses numerical simulations to investigate the hydraulic and thermal performance of spherical dimpled tubes with varying geometric parameters, including dimple pitch, diameter, and the stars. New correlations for the Nusselt number (Nu), friction factor (fr), and performance evaluation criteria (PEC) are developed as functions of these parameters and the Reynolds number. The dimpled tube is analyzed under a constant heat flux of 10 kW/m². The study finds that increasing dimple pitch decreases Nu, fr, and PEC, with deviations ranging from 3 % to 40.5 %, 18.8 %–109.9 %, and −4.2 % to 12.6 %, respectively. Increasing dimple diameter and the number of stars increases Nu and fr, but the effect on PEC varies. Specifically, as dimple diameter increases, Nu changes by 13.1 %–89.3 %, fr rises by 51.9 %–509 %, and PEC varies between −20.2 % and 3.1 %. When the number of dimple stars increases, Nu changes by 21.3 %–45 %, fr increases from 58.7 % to 277.9 %, and PEC improves by 5.3 %–20 %. The results also show that, based on the dimple parameters and Reynolds number, the PEC number can reach a maximum of 1.4.