Numerical study of MHD Casson hybrid nanofluid flow with Brownian and thermophoretic diffusion in porous media

Purpose This study investigates the boundary-layer flow, heat transfer and mass transfer characteristics of a Casson-based hybrid nanofluid over a permeable stretching surface embedded in a porous medium. The analysis includes the effects of magnetohydrodynamics (MHD), Brownian motion, thermophoresis, thermal radiation and variable viscosity. Design/methodology/approach The hybrid nanofluid, composed of aluminum and silver nanoparticles suspended in a Casson base fluid, was modeled using a non-Newtonian rheological framework. The governing partial differential equations were transformed into a system of coupled, nonlinear ordinary differential equations via similarity transformations. This system was solved numerically using a fourth-order Runge–Kutta method combined with a shooting technique. Findings An increase in the Casson parameter enhances resistance to shear, thereby reducing the velocity profile. The Brownian motion (Nb) and thermophoresis (Nt) parameters significantly augment the thermal and concentration boundary layers, increasing wall heat and mass transfer rates by approximately 10–20% over baseline values. The magnetic parameter (M) reduces fluid velocity due to the Lorentz force but increases the temperature gradient at the wall, resulting in a steeper thermal boundary layer. A higher permeability parameter (K1) enhances thermal dispersion while simultaneously suppressing flow speed. An increase in the Prandtl number thins the thermal boundary layer, whereas an increase in the Schmidt number compresses the solutal boundary layer; both trends align with classical transport theory. The combined influence of these parameters reveals complex, nonlinear interactions within the system. Originality/value This study underscores the importance of multiphysics modeling in hybrid nanofluid systems. The extended insights provided can serve as a foundation for designing and optimizing microfluidic heat exchangers, MHD pumps, energy storage units and biomedical devices that utilize advanced nanofluidic flows.