Fractional order unsteady mixed convection in porous-filled concentric pipes: Entropy analysis

This study presents a comprehensive analysis of entropy generation in unsteady mixed convection flow within the annular region of concentric cylindrical pipes filled with a porous medium, incorporating the effects of time fractional order derivatives. The model captures transient thermal-fluid systems' memory and nonlocal impact by employing the Caputo fractional derivative, offering a more accurate representation of real-world behavior. The governing equations are formulated to include temperature-dependent viscosity. They are solved numerically via an implicit finite difference method under appropriate initial and boundary conditions to investigate the influence of key thermophysical parameters. Graphical plots illustrate velocity and temperature profiles, enhancing understanding of fluid behavior. Entropy generation due to heat transfer, fluid friction, and porous media resistance is quantified to assess thermodynamic irreversibilities and identify regions of energy degradation. The results reveal that increasing the fractional order significantly alters the flow and thermal fields, intensifying entropy production and influencing system performance. This research provides valuable insights for optimizing and designing energy-efficient systems involving porous media and time-dependent heat transfer processes, such as geothermal applications, advanced heat exchangers, and thermal energy storage technologies.