Sensitivity Analysis and Mesh Grid Convergence Verification of MHD Casson Hybrid Nanofluid (TiO2-Ag/WEG) Flow and Heat Transport Over a Rotating Stretching Surface

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This study demonstrates a rigorous numerical simulation that maps out the parametric sensitivity analysis, mesh grid independence and structural convergence verification of magnetohydrodynamic (MHD) Casson Hybrid Nanofluid (TiO 2 +Ag-NPs/WEG) flow and heat transfer over a rotating porous stretching surface. The fluid model consists of a 50:50 water and ethylene glycol solution with the addition of titanium dioxide and silver nanoparticles that are widely used for biosensing, medical diagnostics, and photocatalytic devices. The mathematical model is capable of accounting for all the above effects in a comprehensive manner, such as Joule heating, Brownian motion, thermophoresis, space-dependent heat source and exponential activation energy of Arrhenius. The transformed boundary layer ODE's are solved by the adaptive three-step Lobatto IIIa finite-difference formula, which is embedded in the bvp4c collocation solver in MATLAB. Precise grid independence tests demonstrate that the maximum local residual error is always within a convergence tolerance of 10-6 and precisely bounded by the relative error of 10-7 and absolute error of 10-9 when the number of nodes in the system is increased from N = 40 to N = 200\ nodes. The quantitative sensitivity analysis indices computed using response derivatives identify precisely the percentage margins of influence of the competing operational parameters for surface shear stress and wall heat flux. In addition, two-dimensional internal flow streamlines are plotted to trace the trajectory bending of the internal flow which shows the zones of fluid deceleration and cross flow splitting’s of flow trajectories which are rotational. The parametric evaluations show that the influence of the different porosities of the surfaces and magnetic fields restrict the primary flow velocity. The velocity fields enhance with increasing Casson parameters and sheet rotation quantities, but decrease with the inclined magnetic field. In terms of percentage, the local heat transfer rate reduces by up to 12.80% when the magnetic inclination is changed from 20° to 80° while it increases by up to 70.25% and 114.67% upon the increase of the thermal Biot number from 2.0 to 8.0 and the heat source parameter from 0.4 to 1.2, respectively.