Sensitivity based numerical investigation of Hall current and ion slip effects in magneto micropolar hybrid nanofluid flow with activation energy and variable thermal conductivity

This study presents a comprehensive numerical investigation of magneto-micropolar hybrid nanofluid flow over a permeable stretching surface embedded in a porous medium, with particular emphasis on the combined influence of Hall current, ion-slip, activation energy, and variable thermal conductivity. A micropolar fluid- a generalized continuum model that incorporates the micro-rotation of suspended particles- is considered in conjunction with hybrid nanoparticles to capture enhanced thermal and rheological characteristics. These effects become significant under strong magnetic fields or low-density ionized fluids, altering the current distribution and reducing the effective Lorentz force. By employing a similarity transformation, the governing system is solved numerically by the bvp4c MATLAB function, which is based on collocation methods. The parametric study elucidates the role of key dimensionless numbers in shaping the velocity and temperature profiles within the boundary layer regime. Furthermore, the heat and mass transfer characteristics are quantitatively evaluated through the computation of the local Nusselt number and skin friction coefficient. From an application perspective, the outcomes of this research provide insights into the design and optimization of thermal energy systems, polymer extrusion, micro-electromechanical devices, and cooling technologies in porous substrates, where hybrid nanofluids under magnetic fields are utilized to achieve superior performance. The inclusion of activation energy also highlights potential applications in chemical and catalytic processes, particularly in nanofluid-assisted reactors where reaction rates are sensitive to energy barriers. Also, a normalized sensitivity analysis is conducted to obtain the relative sensitivity of the governing parameters on the local Nusselt number, the skin-friction coefficient and the Sherwood number. The analysis shows that the Prandtl number has the largest positive effect (about 75%) on the local Nusselt number, while the micropolar coupling parameter has the highest positive effect (about 48%) on the skin-friction coefficient. Also, the Brownian motion and thermophoresis parameters are important parameters and have a normalized sensitivity close to -100% to +100% for the Sherwood number, respectively