Abstract

This study investigates the unsteady three-dimensional mixed convection flow of a hybrid nanofluid over an expanding or contracting porous disk, taking into account Cattaneo–Christov heat flux, activation energy, and chemical reaction effects. Two types of nanoparticles, metallic (Cu) and non-metallic (Al₂O₃) are dispersed in a water-based fluid, accounting for nanolayer thermal conductivity and internal heat generation. The governing nonlinear partial differential equations are transformed via similarity variables and solved numerically using an optimized shooting method with a fourth-order Runge–Kutta scheme. Results indicate that increasing the mixed convection parameter significantly enhances radial velocity, while a higher buoyancy ratio suppresses it. Activation energy and thermal gradients were found to intensify mass transfer, whereas strong internal heat generation reduces heat transfer efficiency due to thermal resistance. Additionally, higher nanoparticle volume fractions improve momentum transport but may lower thermal and mass diffusivity. These findings contribute to the design and optimization of advanced thermal systems, with real-life applications in rotating thermal reactors, porous catalytic converters, energy harvesting devices, and magnetically controlled nanofluid transport.