Comparative thermal performance of MoS 2 –EG and SiO 2 –EG Casson nanofluids in MHD vertical porous annulus flow with radiation and cross-diffusion effects

Abstract Convective transport of non-Newtonian nanofluids in porous vertical annuli underpins double-pipe heat exchangers, concentric-tube solar collectors, nuclear fuel-rod cooling channels and catalytic packed-bed reactors, yet the combined action of yield stress, non-Darcy drag, variable properties and reactive cross-diffusion in a confined annulus remains poorly quantified. This study develops a nonlinear magnetohydrodynamic model for Casson nanofluid flow between concentric vertical cylinders saturated with a porous matrix, and compares two mono-nanofluids namely MoS 2 –ethylene glycol (EG) and SiO 2 –EG under identical operating conditions so that the influence of nanoparticle chemistry is isolated from that of the flow parameters, both suspensions sharing the same volume fraction, geometry and boundary data. The model retains Casson yield stress, temperature-dependent viscosity, variable electrical conductivity, Brinkman–Forchheimer drag, Rosseland radiation with viscous and Ohmic dissipation, Brownian and thermophoretic migration, Soret cross-diffusion and an Arrhenius reaction with finite activation energy. The dimensionless momentum, energy and species equations are solved by a Galerkin finite-element method with quadratic Lagrangian elements and Newton–Raphson linearisation; grid independence is reached at 150 elements and the solver reproduces five published benchmarks to within 0.01 %. Increasing the Hartmann number, inverse Darcy parameter and Forchheimer inertia suppresses the axial velocity and solutal concentration while raising the temperature through Joule and viscous heating, whereas a larger Casson parameter, variable-viscosity parameter and heat-generation coefficient thicken the boundary layers. Across the whole parameter range SiO 2 –EG returns the higher velocity and Sherwood number, while MoS 2 –EG returns the higher temperature and Nusselt number, so the two fluids are preferable for mass-transport- and heat-transfer-dominated duties respectively. The results provide a quantitative map for selecting the working fluid and operating window of compact annular heat-and-mass exchangers.