Heat and fluid flow dynamics of bioconvective Sutterby octa-hybrid nanofluids under Cattaneo–Christov theory and oblique magnetic field

Purpose This study aims to investigate the combined effects of an inclined magnetic field, nonlinear thermal radiation, Cattaneo–Christov heat flux and entropy generation on the bioconvective flow of a Sutterby octa-hybrid nanofluid over a stretching surface. The analysis further incorporates viscous dissipation, Brownian motion, thermophoresis, motile microorganisms and internal heat generation/absorption to provide a comprehensive thermodynamic assessment of advanced heat transfer systems. Design/methodology/approach The governing nonlinear partial differential equations describing momentum, energy, nanoparticle concentration and microorganism transport are transformed into a coupled system of nonlinear ordinary differential equations using appropriate similarity transformations. The resulting boundary value problem is solved numerically by using the shooting technique in conjunction with the classical fourth-order Runge–Kutta method. The influence of the governing physical parameters on velocity, temperature, concentration, microorganism density, entropy generation and engineering quantities is analyzed in detail. Findings The numerical results demonstrate that the inclined magnetic field suppresses the velocity profile due to the enhanced Lorentz force while simultaneously increasing the fluid temperature through Joule heating. The inclusion of octa-hybrid nanoparticles significantly improves the thermal performance of the base fluid. Nonlinear thermal radiation, viscous dissipation and internal heat generation intensify the thermal boundary layer and increase entropy generation. Furthermore, the Cattaneo–Christov heat flux model accounts for the finite speed of thermal propagation, reducing thermal diffusion compared with the classical Fourier law and consequently modifying the temperature distribution and heat transfer characteristics. Brownian motion reduces nanoparticle concentration, whereas thermophoresis enhances nanoparticle transport within the boundary layer. In addition, entropy generation is highly sensitive to the Brinkman number and temperature difference parameter, indicating their dominant role in thermodynamic irreversibility. Originality/value This work presents a unified mathematical model for the bioconvective flow of a Sutterby octa-hybrid nanofluid by simultaneously incorporating inclined magnetohydrodynamics, nonlinear thermal radiation, Cattaneo–Christov heat flux, entropy generation, viscous dissipation, Brownian motion, thermophoresis, internal heat generation/absorption and motile microorganisms. The proposed model extends existing nanofluid studies by integrating these complex physical mechanisms within a single framework, offering valuable insights for the design and optimization of advanced thermal management systems, solar energy technologies, electronic cooling devices and other engineering applications requiring enhanced heat transfer with improved thermodynamic efficiency.