Computation of casson non-newtonian thermo-magnetic SWCNT/MWCNT-based hybrid nanofluid coating flow from a cylinder with multiple slip and radiative flux effects

Cylindrical components in generators and turbines generate significant heat. Efficient cooling is crucial for performance and extending lifespan. Similarly, cylindrical rollers and propulsion shafts experience high stresses and temperatures in aerospace, industrial and naval applications. Effective coating and thermal regulation are critical in minimizing friction, wear and failure, especially in extreme environments. Nanomaterials offer a robust mechanism for enhancing durability and reducing high temperature corrosion in coatings deployed on such components and can be engineered with a range of functionalities including electromagnetic properties. Motivated by these applications, this study investigates the high temperature external coating thermal convection boundary layer flow of a magnetic non-Newtonian hybrid nanofluid on a cylindrical body. Both single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs) suspended in a base fluid comprising a 50–50% mixture of ethylene glycol and water are studied. A Casson rheological model is employed to simulate non-Newtonian behavior. Thermal radiation flux is simulated with a Rosseland algebraic flux model. Wall slip effects are also considered. The mathematical model is formulated as a set of partial differential equations with associated wall and free stream boundary conditions. This system is reduced to a dimensionless partial differential boundary value problem with appropriate self-similarity scaling transformations. A numerical solution is presented with the Keller box finite difference method, implemented in MATLAB. The simulations show that a stronger Casson rheological parameter suppresses velocity near the cylinder surface but enhances it further away. Temperature and thermal boundary layer thickness are both elevated with Casson rheological parameter and magnetic parameter. SWCNTs achieve superior thermal and flow characteristics for nanocoatings relative to MWCNTs. Flow deceleration and boundary layer cooling are induced with weaker thermal radiative flux effect. Stronger hydrodynamic slip accelerates flow near the cylinder surface but decelerates it further away. Temperature is consistently decreased with greater hydrodynamic slip. Both velocity and temperature are reduced with increment in thermal slip parameter. Skin friction and Nusselt number are also computed and MWCNTs are observed to achieve higher magnitudes than SWCNTs across all values of Casson rheological parameter and along the cylinder length. Streamline contour plots are also presented for various parameters. This work generalizes previous investigations and features novelties via the simultaneous consideration of multiple slip and radiative flux effects in addition to hybrid nanofluids comprising dual base fluids and SWCNTs/MWCNTs and is relevant to functional magnetic nanofluid-based coating deposition on engineering components.