Parametric Study of Natural Convection in a Nanofluid‐Filled Square Cavity Containing a Hexagonal Heated Obstacle Using Multi‐Relaxation‐Time‐Lattice Boltzmann Method

ABSTRACT This study numerically investigates natural convection heat transfer in a square cavity containing a centrally located heated hexagonal obstacle. The cavity is filled with a water‐based nanofluid, that is, water with a suspension of copper nanoparticles. The governing mass, momentum, and energy conservation equations are solved using the lattice Boltzmann method (LBM). A parametric analysis is conducted to quantify the effects of the Rayleigh number, nanoparticle volume fraction, and the obstacle size and orientation (vertical vs. horizontal) on the heat transfer characteristics. The influence commonly attributed to nanoparticle morphology is introduced through the effective thermal conductivity model (via a shape‐factor parameter), and is therefore interpreted as a conductivity‐driven effect. The results show that the average Nusselt number increases with increasing Rayleigh number, increasing nanoparticle concentration, and increasing obstacle size. The highest heat transfer performance is obtained for the horizontally oriented obstacle combined with the highest effective thermal conductivity case. These findings highlight the dominant roles of buoyancy intensity and thermal transport properties, together with obstacle orientation, in enhancing convective heat transfer.