Magnetic Field Influence on the Dynamics of Oxytactic Microorganisms in Swirling Nanoflow: An Interaction of Vortices with the Bacteria

This study presents a numerical investigation of thermo-bioconvection in oxytactic bacteria suspended within a trihybrid nanofluid, with a focus on advancing sustainable thermal management strategies for environmental and energy-efficient applications. The working fluid incorporates a blend of three distinct nanoparticles (Al 2 O 3 , TiO 2 , and others) dispersed in a base fluid, engineered to enhance thermal conductivity while minimizing energy consumption and environmental impact. This approach aligns with green technology principles by utilizing nanomaterials to improve heat transfer efficiency in low-energy systems. The interaction between thermal gradients and oxytactic bacterial motility is analyzed under the synergistic effects of buoyancydriven convection and nanoparticle-induced thermal enhancement, both key mechanisms for sustainable energy utilization in microfluidic and biomedical systems. The governing partial differential equations for momentum, energy, and concentration fields are solved numerically using an energy-efficient computational scheme, reducing computational resource demands. Parametric analysis explores the effects of nanoparticle volume fraction, thermal conductivity ratio, and bacterial motility rate on heat and mass transfer, offering insights for designing eco-friendly thermal control systems. Results demonstrate that trihybrid nanoparticles significantly boost heat transfer, with the Nusselt number increasing by up to 7.5%, largely due to the synergistic effects of Al 2 O 3 and TiO 2 . Enhancing the Reynolds number further amplifies convective performance, with observed increases of 12.4% in Nu and 48.2% in CfRe, indicating reduced thermal resistance and improved system efficiency. Additionally, applying a magnetic field results in a 5.6% improvement in thermal transport, showcasing another controllable, energy-saving factor. Notably, changes in the bioconvection Rayleigh number exhibit minimal influence (<0.5%), suggesting operational stability under varying biological conditions. These findings underscore the potential of trihybrid nanofluids, combined with microbial motility and magnetic control, as environmentally sustainable and energy-efficient solutions for next-generation thermal management in biomedical devices, microchannel heat exchangers, and other green engineering applications.