NUMERICAL INVESTIGATION OF THE HYDROTHERMAL PERFORMANCE OF TURBULENT FLOW IN ELLIPTIC-CONICAL TUBES

Abstract

The need for high thermal performance and compact design of heat exchangers in modern energy and industrial systems is prompting current studies in passive heat transfer enhancement techniques. This study investigated, for the first time, the effect of using elliptic-conical tubes on hydrothermal performance compared with traditional straight-circular tubes under identical operating conditions. A well-validated three-dimensional computational fluid dynamics (CFD) model with the shear-stress transport (SST) $k$-$\omega$ turbulence model is used to resolve the turbulent flow and heat transfer characteristics for both elliptic and conical tubes. The Nusselt number $(Nu)$, friction factor $(f)$, and the performance evaluation criterion (PEC) are determined over a Reynolds number $(Re)$ range of 5,000-50,000. The main focus of the study is to evaluate the influence of different diameter ratios $(DR)$ “1, 1.25, 1.5, 1.75 and 2” on these hydrothermal performance parameters. The findings reveal that, at $DR = 2$ and $Re = 50,000$, the elliptic-conical tubes achieve a 43.5% enhancement in the Nusselt number compared to the traditional straight-circular tube. The results confirm that the elliptic-conical tube configuration provides an effective and promising enhancement in thermal performance, with an optimum design at a diameter ratio of 1.5, for which a maximum PEC of 1.206 is achieved at $Re = 50,000$. The results prove that the elliptic-conical tubes offer a more beneficial hydrothermal performance than straight-circular tubes, especially at high Reynolds numbers. These outcomes encourage the use of elliptic-conical tube geometry in proficient, high-performance heat exchangers.