Enhancing thermal and entropy optimization in bioconvection Casson fluid flow between concentric disks using tri‐hybrid nanoparticles: A finite difference approach

Abstract The flow of fluids containing nanoparticles is essential in industrial applications, particularly in nuclear cooling systems and reactors, where it enhances energy efficiency. This study investigates the transport phenomena of ternary hybrid nanofluids (THNFs), created by mixing a host fluid with three distinct nanoparticles. In this article, nano‐sized particles , , and are mixed in a base fluid, water (). The growing interest in tri‐hybrid nanofluids is due to their remarkable ability to improve thermal performance, making them ideal for heat exchanger applications. The primary objective of this study is to explore the magnetohydrodynamics (MHD), thermal radiation, and laminar mixed convection flow of a tri‐hybrid Casson nanofluid between orthogonally permeable porous disks, incorporating binary chemical reactions with Arrhenius activation energy. Additionally, the study examines the impact of motile microorganisms on flow stability and entropy generation, serving as a measure of thermodynamic irreversibility. The study evaluates the effects of three viscosity models (simple, dynamic, and effective diameter) on skin friction and assesses spherical, non‐spherical, and nanolayer thermal conductivity (TC) models based on Nusselt number variations. The governing nonlinear partial differential equations (PDEs) are transformed into a dimensionless form using similarity variables and solved numerically via the finite difference method (FDM) in MATLAB. Computational results reveal that higher activation energy enhances heat and mass transfer rates, while an increased nanoparticle volume fraction significantly improves skin friction. The nanolayer TC model exhibits superior heat transfer performance compared to spherical and non‐spherical models. Moreover, the interplay of bioconvection and ternary nanoparticles enhances flow stability and thermal transport efficiency. Elevating the magnetic field strength and Casson parameter results in a decline in velocity and entropy generation. As the values of the Schmidt number and Peclet number increase, mass transfer improves, while bioconvection flow decreases. In the variations of different parameters, our analysis indicates that the tri‐hybrid nanofluid exhibits significantly improved flow behavior compared to mono‐ and hybrid nanofluids.