NUMERICAL SIMULATION OF MIXED CONVECTION HEAT TRANSFER AND RESULTING ENTROPY USING TWO VIBRATING CYLINDERS INSIDE A CLOSED CAVITY FILLED WITH Cu-AL2O3-WATER HYBRID NANOFLUID

Abstract

This study investigated the effects of mixed convection heat transfer and entropy generation within a closed two-dimensional square cavity filled with a water-based hybrid nanofluid composed of ammonia and copper nanoparticles, by using Galerkin finite element method. The cavity contains two vertically oscillating cylinders as internal heat sources and cooled outer walls. The effects of Rayleigh numbers (10³-10⁵), oscillation amplitudes (0, 0.05, 0.1, 0.15), and frequencies (0.5,2, 2.5, 5, 10, 20, 40) on flow behaviour, entropy, Bejan number, and local Nusselt number were investigated. The remaining parameters, such as the volume fraction of the nanoparticles (2.5% Cu, 2.5% Al₂ O₃), the shape, position of the cylinders and the Prandtl number (6.2) were kept constant, assuming laminar flow. The results showed that the Rayleigh number was the influential factor in enhancing heat transfer and frequency, while the oscillation amplitude effect was relatively limited, providing a deeper understanding of enhancing heat exchange mechanisms in closed-loop thermal systems with moving internal sources, making them relevant for advanced engineering applications and air conditioning and refrigeration systems. The generation of maximum entropy increased by 23.3% at A=0 and 39.9% at f=40, indicating an increase in the system's non-reflectivity within the enhanced heat transfer range.