Entropy Generation and Bejan Number Analysis in Micropolar Fluid Flow with Variable Thermal Conductivity

Abstract

This study examines entropy generation and Bejan number behaviour in steady, two-dimensional, incompressible micropolar fluid flow over a linearly stretching sheet with variable thermal conductivity. The flow is considered in the presence of a transverse magnetic field and a homogeneous porous medium, with viscous dissipation and heat generation/absorption included in the thermal formulation. The governing boundary-layer partial differential equations are transformed into coupled nonlinear ordinary differential equations by applying suitable similarity transformations. The resulting boundary value problem is solved numerically using the shooting technique combined with the fourth-order Runge-Kutta scheme, and the numerical formulation is validated against limiting cases reported in earlier studies. The effects of micropolar coupling, magnetic field strength, variable thermal conductivity, Prandtl number, and Eckert number are examined through velocity, temperature, entropy generation, and Bejan number profiles. The results indicate that increasing the magnetic parameter retards the velocity field while increasing the temperature distribution and entropy generation near the stretching surface. The micropolar parameter enhances microrotational effects and influences the balance between thermal and frictional irreversibilities. Variable thermal conductivity modifies heat diffusion and shows a comparatively limited effect on the overall entropy generation within the considered parameter range. The Bejan number analysis indicates that the relative dominance of heat-transfer and fluid-friction irreversibilities depends strongly on the governing thermal and magnetic parameters. These results provide a basis for assessing thermodynamic losses in micropolar fluid transport systems.