Abstract

Abstract The purpose of the current research is to inspect the free convection of the nanofluid (Cu–water) within a hexagonal cavity containing a square obstacle with isothermal vertical walls at T h {T}_{{\rm{h}}} and T c {T}_{{\rm{c}}} , and insulated horizontal walls. The aim of this study is to analyze the interaction between the Rayleigh number ( 10 3 < Ra < 10 5 {10}^{3}\lt {\rm{Ra}}\lt {10}^{5} ), obstacle’s position (top, bottom, and center), and volume fraction of the nanoparticles ( 0 < Ø < 0.2 0\lt \O \lt 0.2 ) on the thermal behavior within the enclosure. Simulations were performed using COMSOL Multiphysics software based on the finite element method. The obtained results were demonstrated using streamlines, isotherms, and average Nusselt numbers. It is concluded that the increase in the Rayleigh quantity Ra {\rm{Ra}} and nanoparticle concentration Ø \O increases the average Nusselt N u av {\rm{N}}{{\rm{u}}}_{{\rm{av}}} , which expresses the rate of heat flow in the studied enclosure. Furthermore, the position of the inner obstacle in the middle of the cavity has a more significant thermal efficiency than the other cases.