Mathematical modelling of radiation absorption and Hall–ion slip effects on unsteady magnetohydrodynamic dissipative Casson fluid flow over a vertical permeable plate with chemical reaction and spanwise cosinusoidally fluctuating temperature

The present work investigates the unsteady magnetohydrodynamic flow of a Casson fluid over a vertical permeable plate with a spanwise cosinusoidal temperature variation at the boundary. The model incorporates radiation absorption, Hall and ion-slip currents, and chemical reaction. The governing nonlinear equations for momentum, energy, and concentration are formulated and solved using a regular perturbation technique. The analytical solutions are used to examine the influence of key physical parameters on the velocity, temperature, and concentration fields. The results show that Hall current, buoyancy force, radiation absorption, and heat generation enhance the velocity and temperature distributions, whereas ion-slip effects, magnetic field strength, Schmidt number, and thermal radiation reduce them. An increase in the Casson parameter increases flow resistance, while higher Eckert numbers elevate temperature due to viscous dissipation. The novelty of the study lies in the simultaneous inclusion of spanwise temperature variation along with Hall and ion-slip effects in a dissipative Casson fluid model, which has received limited attention in the existing literature. The findings demonstrate that the interaction of electromagnetic, thermal, and non-Newtonian effects significantly influences flow performance. This study is useful for applications in magnetohydrodynamic cooling, propulsion systems, and microscale transport processes such as microfluidics and targeted drug delivery.