This study explores the entropy generation in the steady flow of water-based nanofluids containing ferromagnetic nanoparticles ( \({\text{Fe}}_{3} {\text{O}}_{4}\) and \({\text{Mn}}{-}{\text{ZnFe}}_{2} {\text{O}}_{4}\) ) over a rotating surface, with a particular focus on the impact of temperature-dependent viscosity variations on flow behavior. The governing equations are numerically solved using the BVP Midrich scheme in Maple software, facilitating the transformation of complex nonlinear differential equations into a dimensionless framework. Key parameters analyzed include viscosity variation, ferrohydrodynamic interactions, Eckert number, Prandtl number, Brinkman number, and particle volume fraction. Results indicate that the manganese-doped zinc ferrite ferrofluid exhibits higher radial velocity than ferrous ferric oxide ferrofluid with increasing stretching parameters, enhancing momentum transport near the surface of the disk. Additionally, an increase in the Brinkman number leads to heightened entropy generation, underscoring a substantial viscous heating phenomenon. The findings offer valuable insights into the thermal and fluid dynamic behavior of ferrofluids, contributing to improved energy efficiency and thermal management in engineering applications.
