Unsteady nonlinear thermal convection flow of MWCNT-MgO/EG hybrid nanofluid in the stagnation-point region of a rotating sphere with quadratic thermal radiation: RSM for optimization

Abstract

The time-dependent enhanced heat transport and nonlinear thermal buoyancy-driven flow of the MWCNT-MgO/EG hybrid nanofluid at the stagnation-point of the rotating sphere subjected to the thermal jump boundary condition are studied theoretically. The quadratic density-temperature variation is also examined together with the quadratic Rosseland thermal radiation. For realistic modelling, experimental data of MWCNT-MgO/EG viscosity and thermal conductivity are used. The monophasic model and the concept of the boundary layer are used to derive the governing partial differential equations, and then they are handled for self-similar solutions using the Finite Element Method (FEM). The effects of driving parameters are examined using 3D contour and surface plots. The further goal of the study is to optimize the heat transport and shear stress of the flow system by applying the central composite-response surface method (RSM) based on the desirability approach. The hybrid nanoparticles volume fraction (NVF) improves friction factors and heat transport. Thermal buoyancy and Coriolis forces condense the thickness of the thermal layer. Heat transport is greater for quadratic thermal convection/radiation than for linear thermal radiation/convection. By RSM, the maximum heat transport (19.0894), the minimum friction factor in the x-direction (2.2564), and the minimum friction factor in the z direction (0.7333) are simultaneously conquered at the low level of NVF, and mixed convection factor and at a high level of QTR factor.