Enhancement of natural convection heat transfer in annular cylindrical enclosure filled with nano fluids: effect of nanoparticle size

In this paper, we present a numerical investigation of natural convection heat transfer in an annular enclosure filled with nanofluid. The inner cylinder, equipped with two symmetrical fins, is subjected to volumetric heat generation, while the outer cylinder is maintained adiabatic. The governing equations for continuity, momentum, and energy are solved using the finite volume method, implemented in Fluent 6.3.26 software. The study evaluates the impact of nanoparticle size and material on the heat transfer rate, considering two water-based nanofluids: Al₂O₃ and TiO₂. A range of solid volume fractions (0 ≤ ϕ ≤ 0.09) and nanoparticle diameters (5 nm, 20 nm, and 80 nm) is analyzed at a Rayleigh number of Ra = 12000. Results indicate that incorporating nanoparticles into the base fluid significantly enhances heat transfer. Among the studied configurations, water/Al₂O₃ nanofluid demonstrates superior heat transfer performance compared to water/TiO₂ nanofluid. Furthermore, smaller nanoparticle diameters lead to more pronounced heat transfer improvements, highlighting the critical role of particle size in thermal performance. These findings provide valuable insights into optimizing nanofluid properties for enhanced natural convection heat transfer in enclosures, with potential applications in advanced thermal management systems.