Analysis of shape effects of hybrid nanofluid TiO 2 – CoFe 2 O 4 / H 2 O with unsteady flow over a rotating disk: Effect of thermal radiation and slip condition

Abstract

In this work, the unsteady flow and heat transfer properties of a hybrid nanofluid consisting of $\mathrm{Ti}{O}_2$ – $\mathrm{CoF}{e}_2{O}_4$ nanoparticles dispersed in water over a rotating disk, that is, stretching radially are investigated. The combined effects of thermal radiation, slip boundary conditions, an applied magnetic field, and different nanoparticle shape are highlighted. This issue is crucial for enhancing heat transfer in complex thermal management systems, where conventional fluids usually perform poorly. Unlike previous studies, this work investigates in a novel manner the effects of different nanoparticle shapes (sphere, column, and lamina) at constant volume fraction under realistic operating conditions on flow resistance and thermal performance. The governing Navier–Stokes and energy equations were numerically solved using MATLAB’s BVP4C solver and the Von Kármán similarity transformations. The results show that increasing the radiation parameter improves the temperature profile and makes cooling more efficient, but increasing the Prandtl number makes it less efficient. The Lorentz force causes higher magnetic fields to boost fluid temperatures and lower axial, tangential, and radial velocities. As the slip parameter increases, the fluid speeds decrease and the temperature of the wall increases. These findings demonstrate that spinning disc systems can flow and transfer heat more effectively by selecting the appropriate boundary slip and nanoparticle shape. Effective cooling systems and heat exchangers depend on this. The fluid rotating in front of the disk rotates more slowly when the unsteadiness parameter $\hat{\alpha }$ has a lower value.