EFFECTS OF VARIABLE VISCOSITY AND THERMAL CONDUCTIVITY ON MOTION OF CASSON NANOFLUID THROUGH A RIGA SURFACE WITH HEAT FLUX THEORY

This study examines the influence of variable viscosity and thermal conductivity on the flow and heat transfer characteristics of Casson nanofluid over a Riga surface embedded in a porous medium, incorporating the Cattaneo–Christov heat flux model. The governing partial differential equations, formulated under the Boussinesq and boundary layer approximations with consideration of nonlinear buoyancy, first-order chemical reaction, thermophoresis, and Soret–Dufour effects, are transformed into a system of ordinary differential equations using similarity transformations. These equations are solved numerically via the Chebyshev spectral collocation method. Parametric investigations reveal that increasing the modified Hartmann number enhances the velocity profile and hydrodynamic boundary layer thickness, while higher Casson parameters elevate skin friction but resist fluid motion under constant viscosity and thermal conductivity. Elevated Prandtl and Schmidt numbers suppress both velocity and temperature fields, whereas greater thermal radiation, Eckert number, and thermal relaxation time enhance thermal boundary layer growth. Variable viscosity is found to intensify fluid motion, and variable thermal conductivity amplifies both temperature and velocity distributions. Results also highlight the opposing roles of chemical reaction and thermophoresis parameters on concentration and velocity fields. Comparison with previous studies confirm the accuracy of the present model. The findings provide valuable insight into the behaviour of non-Newtonian nanofluids under complex thermal and magnetic conditions, with potential applications in energy systems, biomedical flows, and advanced material processing.