Unlocking heat transfer potential in multi-sided porous geometries: A study on magnetothermal effects and entropy generation

• Multi-sided porous geometries enhance heat transfer in magneto-nanofluid systems. • Hexagonal structures rival circular tubes in space-constrained thermal applications. • Pentagonal cavities show the highest irreversibility due to asymmetry effects. • Heatline visualization reveals complex thermal energy transport dynamics. • Optimized geometry and parameters boost heat transfer while minimizing entropy. This study investigates heat transfer efficiency and irreversibility generation in multi-sided porous thermal systems filled with a Cu-Al 2 O 3 -water hybrid nanofluid. The research examines convective heat transfer across various polygonal geometries, ranging from four-sided to infinitely-sided (circular) structures, aiming to maximize thermal system performance intended for scientific and industrial applications. For a standardized comparison, the fluid volume and active heating and cooling lengths are kept constant for all the geometries considered. The analysis includes varying flow-controlling variables like the modified Rayleigh number (Ra m ), Hartmann number (Ha), and Darcy number (Da) to evaluate how they affect heat transfer efficiency and entropy generation, including total, magnetic, and viscous entropy. The numerical simulations, conducted using the finite element approach, explore Ra m values ranging from 10 to 10 4 , Ha from 0 to 70, and Da from 10 -4 to 10 -2 . Streamline and isothermal contours analyze flow behavior, while heatline tools reveal thermal energy transport dynamics. Results show up to a 20% improvement in heat transfer efficiency in optimized configurations. Key findings indicate that hexagonal structures can be viable alternatives to circular tubes in space-constrained applications, offering comparable thermal performance. Interestingly, pentagonal cavities exhibit the highest irreversibility due to symmetry loss. The study offers insightful information for enhancing thermal system design in various industrial settings, particularly for applications requiring efficient heat transfer in limited spaces.