Analysis of Mixed Convection and Entropy Generation with a Rotating Half-Immersed Cylinder: Effects of Nanofluid, Magnetic Field, and Internal Heat Generation

This numerical study presents a comprehensive investigation of mixed convection, thermal mechanism and entropy generation in a novel cavity system featuring a rotating, heat-conducting, half-immersed cylinder. The enclosure is filled with Cu-water nanofluid and driven by the combined effects of an inclined magnetic field and internal heat generation. The effects of key parameters-nanoparticle volume fraction ( Φ = 0% to 4%), magnetic field inclination angle ( γ = 45°, 60°, 80°), internal heat generation coefficient (Δ = 0, 3), and Grashof number (10 3 to 10 7 ) are systematically investigated. The major findings reveal that nanoparticle inclusion enhances heat transfer but increases thermodynamic irreversibility. Specifically, at Gr = 10 7 , a Φ of 4% yields a 4.3% higher Nusselt number compared to a 1.5% concentration, yet it also elevates entropy generation. The magnetic field orientation demonstrates a critical regime-dependent influence: at high Gr, a γ = 45° angle maximizes heat transfer (providing a 10% higher Nusselt number than γ = 80°), whereas a γ = 80° inclination optimizes thermodynamic efficiency by reducing entropy generation by approximately 8%. Most critically, internal heat generation is found to be profoundly detrimental, suppressing the Nusselt number by 43% at Gr = 10 3 and exacerbating entropy generation by over 11,000% in the conduction-dominated regime. The Thermal Performance Criterion analysis conclusively determines that for optimal heat transfer, a high nanoparticle concentration ( Φ = 4%) with a magnetic field at γ = 45° is recommended, while for superior thermodynamic performance, a lower concentration ( Φ = 1.5%) with a γ = 80° field is ideal. This research provides definitive guidelines for designing high-efficiency thermal management systems by leveraging hybrid nanofluid-magnetic field control, while underscoring the imperative to minimize internal heat generation.