Mixed convection of Fe ₃ O ₄ –MoS ₂ /EG nanofluids in a porous cylindrical annulus with thermally dependent viscosity and electrical conductivity

Abstract This study investigates coupled heat and mass transfer in mixed convection of Fe 3 O 4 –ethylene glycol and MoS 2 –ethylene glycol nanofluids within a porous cylindrical annulus, a geometry that fundamentally alters nanoparticle migration compared with planar configurations. The model simultaneously incorporates activation energy controlled chemical reactions, temperature-dependent viscosity, thermo-diffusion (Soret effect), thermal radiation, and radiation absorption. Numerical results reveal that thermo-diffusion redistributes nanoparticles away from both annular walls, leading to a reduction in Sherwood number by up to 18 % even when thermal gradients intensify, while thermal radiation enhances the temperature field and increases the Nusselt number by approximately 15 %. Radiation absorption raises the bulk temperature without a proportional increase in nanoparticle flux, confirming a decoupling between heat and mass transport. Increasing activation energy promotes nanoparticle accumulation near the walls but reduces heat transfer, causing the Nusselt number to decrease by nearly 12 %. The presence of dual confining walls further produces asymmetric heat and mass transfer rates between the inner and outer cylinders. These findings demonstrate that annular nanofluid transport cannot be inferred from single-surface models and provide new insights relevant to annular heat exchangers, reactor cooling channels, and energy-storage systems.