Double-Diffusive Heat and Mass Transfer in Unsteady MHD Casson Nanofluid Flow over a Bidirectional Stretching Surface with Cattaneo–Christov Heat Flux

This work presents a theoretical investigation on unsteady magnetohydrodynamic (MHD) boundary layer flow of Casson nanofluids over a bidirectional stretching surface, with an emphasis on double-diffusive heat and mass transfer. To overcome the limitation of classical Fourier’s law, the Cattaneo–Christov heat flux model is employed to consider thermal relaxation time and finite heat propagation velocity. The mathematical model fully couples multiple physical mechanisms including thermal radiation, viscous dissipation, porous medium effect, Brownian motion and thermophoresis. Based on similarity transformations, the partial differential equations governing mass, momentum, energy and concentration are converted into a set of coupled ordinary differential equations. The calculated results are proven to be reliable through comparison with previous research outcomes. We systematically discuss the effects of various dimensionless parameters on flow field, temperature field and nanoparticle concentration field. It is observed that magnetic field, porosity and unsteadiness suppress flow velocity, while a larger Casson parameter enhances fluid movement. Temperature distribution is elevated by thermal radiation, viscous dissipation, Brownian motion and thermophoresis, and reduced by thermal relaxation. Concentration decreases with increasing Schmidt number and Brownian motion parameter, but increases with the rise of thermophoresis parameter. Furthermore, the growth of thermophoresis leads to a reduction in skin friction coefficient, local Nusselt number and local Sherwood number. This research deepens the understanding of multi-physical coupled transport in non-Newtonian nanofluids, and the results have broad application prospects in biomedical equipment, polymer production, heat exchangers and energy engineering.

کلیدواژه ها:

double diffusion ، heat and mass transfer ، MHD flow ، Casson nanofluid ، Cattaneo–Christov heat flux ، bidirectional stretching surface ، thermal radiation ، viscous dissipation