MHD natural convection and entropy generation in star-shaped porous cavities with hybrid nanofluids: effects of magnetic field inclination and radiation

Purpose This study aims to examine how natural convection heat transfer and fluid movement function within star-shaped porous cavities containing Fe3O4-Al2O3/water hybrid nanofluid while being subjected to magnetic fields and thermal radiation. The study examines how magnetic field inclination and hybrid nanofluids interact with star-shaped geometries containing three, four, five and six points to enhance heat transfer mechanisms within intricate structures. This research investigates how geometry and multiple physical effects impact system performance to enhance thermal efficiency in irregular enclosure settings. In addition, the study explores entropy generation and the Bejan number to evaluate thermodynamic irreversibilities across geometries. Design/methodology/approach The development of a two-dimensional numerical model enabled the resolution of steady-state equations governing mass, momentum and energy conservation. The research varied key dimensionless parameters such as the Rayleigh number (Ra), Hartmann number (Ha), thermal radiation (Rd) and nanoparticle volume fraction (ϕ) to determine their influence on the stream function (Ψ), temperature field (θ), entropy generation (Sgen), Bejan number (Be) and Nusselt number (Nu). The finite element method enabled numerical simulations, which led to the creation of an empirical correlation for average Nusselt number and entropy generation using Ra, Ha and ϕ parameters. Findings The six-point star geometry achieves the most homogeneous heat distribution, whereas the three-point star geometry achieves maximum localized heat transfer enhancement when magnetic field inclination reaches p/2. Localized Nusselt number enhancement reaches up to 37% from the three-point star configuration when influenced by magnetic field inclination. The six-point star geometry achieves up to 42.6% higher average Nusselt number when the nanoparticle volume fraction rises from 0% to 30%. The research illustrates how buoyancy-driven flow, magnetic damping and improved thermal conductivity from nanoparticles combine to affect thermal performance, while entropy maps and Bejan number fields offer insights into irreversibility patterns. The empirical correlations created during this study serve as tools to predict and optimize both heat transfer and entropy generation performance. Originality/value The investigation provides novel understanding of how hybrid nanofluids interact with magnetic field orientation and atypical porous cavity forms. The study’s systematic analysis of star-shaped cavities reveals a new method to boost thermal performance in complex shapes. Current literature lacks studies that combine magnetic field inclination, radiation effects and hybrid nanofluids in star-shaped cavities. The new empirical correlation alongside performance maps offers valuable tools for designing thermal systems that include solar collectors and electronic cooling systems as well as porous enclosures with complicated geometries, where managing both heat transfer and thermodynamic irreversibility is critical.