Analysis of turbulence and heat transfer parameters inside the twisted multi-lobed tubes: A computational fluid dynamics study

Understanding how geometric modification alters turbulence and heat transfer in internal flows is essential for the physics-based design of high-performance thermal systems. This study presents a numerical investigation of turbulent flow and convective heat transfer in twisted multi-lobed tubes, focusing on the combined influence of lobe number (bi-, tri-, and quad-lobe), roundness factor, and twist angle on flow structure and thermo-hydraulic behavior. Simulations are conducted for Reynolds numbers between 5000 and 15000 using water as the working fluid. The results demonstrate that increasing the lobe number strengthens secondary flow and redistributes turbulence across the cross section, leading to enhanced mixing and wall heat transfer. For the optimal quad-lobe geometry, the average heat transfer rate increases by up to 83.9% compared with a smooth tube, accompanied by a friction factor increase in up to 51.3%. When heat transfer enhancement and pressure loss are evaluated together, a moderately rounded quad-lobe tube achieves the highest overall performance, with a maximum performance evaluation criterion of 1.43 at the Reynolds number of 5000. The effect of twist angle (180°–540°) shows that stronger twisting intensifies swirl and boundary layer disruption, increasing heat transfer; however, the associated pressure penalty grows nearly linearly, yielding diminishing net gains beyond an optimal twist range. Analysis of turbulent momentum and heat fluxes reveals that enhanced turbulent transport and secondary flow interaction are the dominant physical mechanisms governing the observed trends. By systematically varying geometry and twist within a unified framework, this work extends previous studies limited to single shapes or twist conditions.