TAGRA 2025

With the increasing importance of heat transfer applications, the development of new methods to increase energy efficiency and reduce energy consumption has become inevitable. In this context, the use of nanofluids as an alternative heat transfer medium offers higher heat transfer performance compared to conventional fluids, thereby reducing energy losses. Entropy analysis, a measure of energy quality, plays a critical role in evaluating the effectiveness of energy conversions in thermodynamic systems. Because entropy production represents the level of irreversibility and energy losses of a system, it stands out as an important parameter in the performance analysis of energy systems. In this study, the behavior of water–Al₂O₃ (aluminum oxide) nanofluid with variable thermophysical properties, within a square chamber with a moving and cold top wall, a fixed and hot bottom wall, and insulated side walls, was numerically investigated under natural convection conditions in terms of entropy production. Simulations were performed for a fixed Grashof number (Gr = 10⁴), three different Reynolds numbers (Re = 100, 300, and 600), and two different nanoparticle volume fractions (ϕ = 0.01, 0.02, 0.03, and 0.04). The results revealed that total entropy production increased with increasing nanoparticle volume fraction at all Reynolds numbers examined. Furthermore, when the entropy production components were evaluated, it was determined that entropy production due to friction was negligible, and the largest contribution to total entropy production came from entropy production due to heat transfer.