Impact of Lewis Number on Natural Convection with Double Diffusion in a Square Cavity Filled with Non-Newtonian Fluid with Viscosity Varying with Temperature

This work focuses on the numerical analysis of double diffusive natural convection inside a square cavity filled with non-Newtonian fluids obeying the power-law model. The viscosity is considered to vary with temperature following an exponential law. The main parameters studied are the Lewis number, thermo-dependent parameter, and behavior index. It was observed that increasing the thermo-dependent parameter intensifies the flow, which leads to a significant improvement in heat and mass transfer within the cavity. When the thermo-dependent parameter is increased from 0 to 3, the average Nusselt number increases by 109% for low Le, while the Sherwood number rises up to 108%, reflecting a significant intensification of heat and mass transfer. This intensification is further enhanced when the behavior index decreases from 1.4 to 0.6, which increases flow intensity due to the decrease in apparent viscosity in high shear areas. Furthermore, a high Lewis number reduces heat transfer but greatly increases mass transfer.