This study presents a novel analytical investigation into entropy generation in a magnetohydrodynamics (MHD) Couette flow of Casson fluid subjected to mixed convection and governed by a two-step exothermic chemical reaction. The analysis incorporates three distinct chemical kinetics models: Sensitized, Arrhenius, and Bimolecular, to understand their impact on heat and mass transfer processes. Unlike traditional single-step combustion analyses, this work uniquely considers non-Newtonian rheology, magnetic field effects, and complex chemical kinetics in a transient flow, offering a more realistic and industrially relevant perspective. To obtain an analytical solution for the dimensionless non-linear governing equations, the study employs the Laplace transform method combined with the differential transform technique. The effects of key flow parameters on velocity distribution, thermal distribution, and entropy generation are illustrated through graphical representations; also the influence of activation energy across different chemical kinetic models is analyzed using graphs. In addition, numerical values for the heat transfer rate and shear stress on both the lower and upper plates are presented in tabular form. The findings indicate that entropy generation can be effectively minimized during the two-step exothermic reaction. This research has important implications for optimizing thermal management in MHD systems, enhancing combustion stability in catalytic converters, and improving energy efficiency in industrial processes involving complex reacting non-Newtonian fluids, such as in automotive exhaust treatment, chemical reactors, and metallurgical applications.
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