Magnetohydrodynamic double-diffusive convection of hybrid nanofluids in a U-grooved trapezoidal cavity

A three-dimensional numerical study was developed to examine double-diffusive convection in a trapezoidal cavity with a U-shaped heated groove, filled with an Al2O3–Cu/water hybrid nanofluid. A finite element method is employed to solve the governing equations over a range of Rayleigh numbers (104–105), Hartmann numbers (0–100), buoyancy ratios (N = −2, 0, 2), and nanoparticle volume fractions (0%–4.5%). The results show that the groove acts as a focal point for the development of the Lorentz force, whose intensity increases near its lower edges under strong magnetic fields (Ha = 25, Hartmann number), suppressing convection and favoring conduction-dominated regimes. The distribution of electric potential, which is confined in the absence of nanoparticles, becomes more complex in the presence of nanofluids (φ = 4.5%), showing alternating charge zones due to induced currents and increased mixing. Heat and mass transfer are strongly influenced by the interaction between geometry, buoyancy, and magnetic damping. The U-shaped groove improves convective transport under favorable conditions while stabilizing stratified layers under unfavorable conditions. These results show that magnetohydrodynamic-nanofluid coupling in geometric cavities could be used to make compact, passive, and adjustable thermal control systems that work well in spacecraft and microgravity settings. Heat and mass transfer are strongly influenced.