An examination of the entropy generation of nanofluids and the natural convection dynamics within a circular cavity influenced by a cold fluid jet

Abstract

Currently, cavities serve as one of the most prevalent methods for managing and dissipating heat produced by centralized indoor sources. The examination of fluid dynamics within cavities influenced by external cold flows has not garnered significant attention from scholars. This study focuses on a cavity with a unique geometry designed to regulate an internal heat source within a spherical buffer via flow injection. The temperature variations within the enclosure affect the flow through the outer shell via the convection heat transfer process. This distinctive heat transfer configuration distinguishes the findings of this research from those of previous studies. The heat transfer and flow dynamics will be simulated for Rayleigh numbers ranging from 100 to 1000. The nanotubes under investigation will have volume fractions between 0 and 0.06 and will exist as a stable solution. The research employs the finite volume method in a two-dimensional steady-state framework. The findings of this study show that the temperature changes between the surface of the circular shell and the hot source will result in natural convection heat transfer. According to the geometrical conditions of the hot circular surface, which side of the cavity experiences stronger fluid movement will result in a better heat transfer distribution. In Reynolds numbers ( Re ) = 300 and 700, strengthening the buoyancy force as an effective factor in improving the Nusselt number ( Nu ) can increase it by more than 1.5 times. At Re = 100, increasing the volume fraction of solid nanoparticles ( φ ) will also increase Nu by 4 %. For Re = 300 and 700, compared to the base fluid, using a nanofluid with φ = 6 % improves Nu by 8 %. With the increase of Re , due to the strengthening of the fluid inertia, the amount of changes in layer velocity will decrease, and finally, the friction factor (C f ) will decrease. In geometries similar to the investigated problem, reducing C f is possible only by the external enhancement of the velocity, such as increasing Re in the injected flow outside the cavity. The presence of solid nanoparticles increases density and viscosity, while also improving temperature distribution. Increasing Ra can strengthen a more uniform velocity distribution with fewer velocity gradients in the cavity, especially in the areas near the wall. The changes of Cf loc depend on velocity gradients near the hot wall. In all the investigated cases, in the places where hot surface experiences flow separation, the lowest Cf loc will be created.