Bioconvection driven flow of magnetized micropolar hybrid nanofluid with Ohmic heating and variable thermal conductivity.

Bioconvection in hybrid nanofluid(HNF) flow arises from the collective, upward swimming of motile microorganisms (bacteria, algae, and fungi) suspended in a base fluid that also contains diverse types of nanoparticles. This phenomenon generates spontaneous, gravity-driven flow patterns such as plumes, cells, or vortices that significantly modify the fluid's thermal and mass transport characteristics. Understanding this process is vital for advancing applications in biomedical engineering, environmental science, and energy systems. In this study, the dynamics of bioconvective engine oil-based HNF flow by a porous stretched sheet under the impact of magnetic force is investigated. The hybrid nanofluid is formulated by suspending rigid nanoparticles of alumina (Al2O3) and gold (Au) in the base fluid. The micropolar fluid model is chosen for analysis. Influences of heat source effects, magnetic field, dissipation, and thermal radiation are accounted in the formulation. Using the local non-similarity approach, the governing dimensional system is transformed into a set of dimensionless, nonlinear, coupled differential equations. The NDSolve function of Mathematica is used to investigate the influence of diverse variables on HNF thermal, velocity, microrotation, concentration, and motile density profiles. The numerical results reveal that the hybrid nanofluid enhances the surface skin-friction coefficient by up to 10%, the heat transfer rate by approximately 19%, and the motile microorganism transfer rate by nearly 6% compared with the corresponding mono nanofluid. These findings demonstrate the superior thermal and transport performance of engine oil-based hybrid nanofluids, highlighting their potential for advanced heat transfer systems and bio-inspired engineering applications.