CFD Comparison of Nanoparticles Concentration and Geometrical Effects on the Heat Transfer of Gaseous Nanofluid Flows in the Annulus of Two Cylinders

High performance of cooling systems is an essential engineering requirement for lots of modern industrial applications for heat discharge necessity. This work employs CFD simulations to study the heat transfer due to natural convection in laminar flows, both with and without the presence of artificially suspended alumina (Al2O3) nanoparticles in the air. This paper focuses on how the radial heat transfer is impacted by the dimensionless numbers of Knudsen (Kn), Rayleigh (Ra), annulus size, i.e. Aspect Ratio (AR), and content percentage (φ) of the alumina nanoparticles. The set of equations that govern the heat transfer in this study is solved using a finite volume simulation technique, considering the effect of buoyancy through the Boussinesq approximation. It is found that adding 1% of alumina nano materials (φ = 1%) significantly improves heat transfer rates throughout the ranges of physical characteristics taken into account in this investigation. Additionally, it is noted that for φ > 4% and Ra > 104 across the tested range of, a negligibly increased heat transfer is attained. Heat transfer is shown to rise when Kn number decreases (average Nusselt number grows) (AR and Ram remain constant), and to decrease as AR increases (φ and Ram remain constant).