Numerical investigation of bioconvective cross nanofluid flow over a stretching cylinder using Buongiorno's model

This study aims to develop and examine the combined impacts on boundary-layer flow and heat transfer features of non-Newtonian Cross fluid rheology, Buongiorno's nanofluid model, bioconvection, and enthalpy transport under a heat source/sink regime. The flow is developed in a cylindrical coordinate system because Cross fluid is assumed to be moving on the stretching cylinder, with the Buongiorno nanofluid model that encompasses the Brownian motion and the thermophoretic diffusion as the most prominent mechanisms of transportation of nanoparticles in the flow. The microorganisms are assumed to be gyrotactic, and their motion is influenced by fluid velocity and concentration gradients. The Cross rheological model explains the shear-thinning and shear-thickening properties of the fluid, and the suspension is stabilized by bioconvection caused by motile microorganisms. To simulate realistic heat transfer behavior, the effects of internal heat sources/sinks and enthalpy change are incorporated. The thermal and solutal slip boundary conditions are assumed at the surface of the stretching cylinder. The current work is novel because it simultaneously integrates Cross fluid characteristics with microorganism-induced bioconvection and Buongiorno's nanofluid model, taking into account enthalpy changes and heat source/sink effects. The similarity variables are introduced, which convert the governing equations of momentum, energy, and concentration as well as microorganism density in the form of dimensionless equations, and then solved numerically via the fifth-order Runge-Kutta (RK) method with the shooting approach on Matlab software. The findings indicate that the velocity field decreases with the increase in Weissenberg number, but the bioconvection and buoyancy parameters improve the flow and heat transfer. Motile microorganisms increase bioconvection, which improves fluid mixing but lowers the density of microorganisms near the surface. The findings show that the augmentation in thermophoresis considerably enhances both temperature and concentration profiles, whereas an increase in the Brownian motion parameter improves the temperature distribution while decreasing nanoparticle concentration. In general, the paper emphasizes the synergistic interactions of non-Newtonian rheology, nanoparticle transport, bioconvection, and enthalpy over the stretching cylinder, which have applications in industrial and biomedical processes. The results of this work have important practical applications in advanced thermal management systems, such as cooling electronic devices, biomedical engineering procedures like medication administration and microbial movement, and energy systems like nuclear reactors and solar thermal collectors.