Investigation of entropy generation in unsteady flow of Casson nanofluid over a rotating stretchable disk

A B S T R A C T Aerodynamic devices, chemical reactors, and industrial heating systems all primarily rely on unsteady boundary layer flows over rotating and stretchy surfaces. The thermodynamic behavior and energy efficiency of a laminar, incompressible, unsteady Casson nanofluid flow caused by a spinning stretchable disk are investigated in this work. Through similarity transformations, the governing partial differential equations (which take into account the combined physical effects of a transverse magnetic field, thermal radiation, viscous dissipation, Joule heating, and chemical reactions) are transformed into a non-linear ordinary differential system and solved using a numerical collocation method. The main contribution of this study is the simultaneous formulation of geometric surface stretching, dynamic unsteadiness, and multi-component entropy generation in a non-Newtonian Casson nanofluid, which is a unique addition to traditional decelerating disk flow models. Key findings show that a greater stretching value significantly accelerates the boundary layer flow, but an increasing unsteadiness parameter decreases fluid velocity, temperature, and concentration distributions. Additionally, it is demonstrated that the main causes of maximized thermodynamic irreversibility close to the disk surface are increased magnetic and group parameters .