The purpose of this study is to investigate the influence of Hall current and magnetic field on heat and mass transfer characteristics in a bioconvective magnetohydrodynamic (MHD) nanofluid flow within a porous square cavity containing gyrotactic microorganisms. Such configurations are relevant to magnetically controlled bio-reactors, microscale cooling systems and nanofluid-based thermal management devices.
Finite difference method with Gauss–Seidel iterative approach is used to solve the coupled governing equations of momentum, energy, nanoparticle concentration and microorganism density. Darcy porous medium model is used in momentum equations. The effects of key dimensionless parameters, including the Peclet number, buoyancy ratio, Darcy number, Hartmann number and Hall current parameter, are systematically analysed through streamlines, temperature contours, nanoparticle volume fraction distributions and microorganism isoconcentration profiles.
The Hall current alters flow patterns by increasing velocity and splitting circulation cells, while reducing overall heat and mass transfer. Decreasing the Darcy number from 0.1 to 0.001 lowers flow strength by approximately 26%. Increasing the Peclet number from 0.1 to 0.2 enhances convection, improving nanoparticle concentration about 47% and promoting microorganism mixing. Higher buoyancy ratios intensify bioconvection and strengthen circulation. In contrast, raising the Hartmann number from 10 to 20 suppresses fluid motion due to magnetic damping. This results in 67% reduction in the maximum flow velocity and a transition towards a conduction-dominated heat transfer regime. Overall, the average Nusselt and Sherwood numbers increase with Darcy and Hartmann numbers but decrease with the Hall parameter.
This study presents a novel numerical investigation of bioconvective flow in a Darcy model porous cavity by simultaneously incorporating Hall current, magnetic field effects, nanofluid and gyrotactic microorganism dynamics. While previous studies have examined MHD nanofluid convection, Hall current effects or bioconvection separately, their combined influence within a porous enclosure has received very limited attention. The findings provide new physical insight into MHD bioconvection control mechanisms. These are valuable for the design of bioinspired thermal systems, energy devices and microscale transport applications involving nanofluids in porous environments.
