The effect of a flat tube with different aspect ratio and inclination angle on natural convection inside a square enclosure

This paper analyzed the effect of a flat tube with various aspect ratio (AR) and inclination angle (φ) inside a square enclosure on natural convection. The study covered the Rayleigh number (Ra) from 103 to 106 and a Prandtl number (Pr) of 0.7. The aspect ratio of the flat tube was changed from 0.5 to 2.5 in intervals of 0.5, while the inclination angle ranged from 0° to 90° in intervals of 15°. All simulated cases achieved a steady state, though the thermal and fluid flow characteristics exhibited slight variations depending on the simulation parameters. The value of AR and φ of the flat tube notably influenced heat transfer performance. Specifically, \(\overline{\text{NY}}_{\text{cy}}\) $${\overline{\text{NY}}}_{\text{cy}}$$ increased by up to 5.56 % and 6.96 %, respectively, across the entire range compared to the circular cylinder. Furthermore, correlation equations of the Nusselt number were developed to predict the heat transfer performance on both the flat tube and the enclosure. These equations provide a comprehensive understanding of how Ra, AR, and φ affect heat transfer performance in two-dimensional natural convection system.