Unsteady entropy generation in nanofluid flow inside a square cavity with chemical reaction, radiation and Cattaneo–Christov heat flux

Purpose This study aims to investigate entropy generation in unsteady Buongiorno’s model nanofluid flow inside a square cavity under the combined effects of thermal radiation, chemical reaction and Cattaneo–Christov heat flux, with emphasis on thermodynamic irreversibility. Design/methodology/approach The governing time-dependent equations incorporating Brownian motion and thermophoresis are formulated using Buongiorno’s nanofluid model. The coupled nonlinear equations are solved numerically via the finite element method. The effects of thermal relaxation, radiation and chemical reaction parameters on velocity, temperature, concentration and entropy generation are examined. Findings Increasing thermal relaxation time reduces temperature gradients and consequently lowers entropy generation. Radiation intensifies thermal irreversibility by enhancing heat transfer within the cavity. Brownian motion strengthens nanoparticle diffusion, leading to higher entropy production. The interaction between radiation and relaxation parameters significantly influences overall thermodynamic performance. Research limitations/implications The analysis is limited to two-dimensional laminar flow in a square cavity, suggesting future extension to complex geometries and turbulent conditions. Practical implications The outcomes support optimization of nanofluid-based thermal management systems by reducing entropy generation and improving efficiency. Social implications Improved thermodynamic efficiency contributes to sustainable energy utilization and environmentally responsible thermal system development. Originality/value This study simultaneously incorporates unsteadiness, Cattaneo–Christov heat flux, radiation and chemical reaction within Buongiorno’s nanofluid framework to evaluate entropy generation. The results provide deeper insight into controlling irreversibility in nanofluid-filled enclosures for energy-efficient thermal system design.