Numerical simulation of double-diffusive convection in hybrid nanofluid flow in a porous medium within a swastika-shaped cavity

Purpose This study aims to examine double-diffusive natural convection (DDNC) in a swastika-shaped porous cavity filled with a hybrid nanofluid (Fe 3 O 4 -GO/water). It aims to analyze heat and mass transfer under varying thermophysical properties and key parameters like Rayleigh (Ra), Darcy (Da), Lewis (Le), Schmidt (Sc) numbers and buoyancy ratio (N). The research seeks to evaluate the hybrid nanofluid’s performance compared to mono nanofluids, providing insights for applications in cooling systems, heat exchangers and chemical processing. The study addresses the gap in understanding hybrid nanofluid behavior in complex porous geometries under combined thermal and solutal buoyancy effects. Design/methodology/approach The coupled partial differential equations for mass, momentum, energy and species concentration are solved using a stable, higher-order finite element method (FEM). Temperature- and concentration-dependent thermophysical properties of the hybrid nanofluid are incorporated. The FEM code is validated against experimental data and numerical benchmarks. The important parameters are systematically varied to assess their impact on heat and mass transfer. Performance metrics such as average Nusselt number ( Nu avg ), Sherwood number ( Sh avg ) numbers and kinetic energy ( KE avg ) are analyzed to compare hybrid and mono nanofluids under different porous media conditions. Findings Increasing buoyancy ratio (N) from 0–4 enhances Nuavg (8.30%–8.36%), Shavg (14.61%–15.01%) and KEavg, highlighting solutal buoyancy’s strong influence. Higher Ra transitions the system from conduction- to convection-dominated regimes, with Nuavg rising by 50.89% and Shavg by 65.20% at Ra = 106 as Da increases (10–5–10–2). The hybrid nanofluid outperforms mono nanofluids, with Nuavg increasing by 0.28%–1.46% and Shavg by 0.08%–0.40% as nanoparticle volume fraction (?) rises (0.01–0.05). These results demonstrate the hybrid nanofluid’s superior thermal and solutal transport capabilities in porous media. Originality/value This study presents novel insights into DDNC of hybrid nanofluids in a uniquely shaped porous cavity, addressing a gap in existing literature. The temperature- and concentration-dependent modeling of hybrid nanofluid properties enhances accuracy. The validated FEM approach ensures reliability for complex geometries. Findings reveal significant improvements in heat and mass transfer due to hybrid nanoparticles, offering practical benefits for industrial applications like advanced cooling and chemical processing. The quantitative analysis of key parameters provides a benchmark for future studies, emphasizing the hybrid nanofluid’s potential to outperform conventional fluids in porous media systems.