Cu-Al2O3 hybrid nanofluid natural convection in an inclined enclosure with wavy walls partially layered by porous medium

A parametric numerical investigation is performed of the natural convection and heat transfer in an enclosure with opposing wavy walls, layered by a porous medium, saturated by a hybrid  nanofluid, at different inclination angles. The Galerkin finite element method is used to obtain  steady-state solutions of the heat and mass convection laws by application of the semi-implicit method for pressure linked equations algorithm. The Darcy-Brinkman model is used for representing the state variables change in the porous layer. The influence of six parameters on the flow and heat transfer rate is described. These are the inclination angle, varied from 0^o to 90^o, the 

Rayleigh number (10⁴ ≤ 𝑅𝑎 ≤ 10⁷), the Darcy number (10^-5 ≤ 𝐷𝑎 ≤ 10^-2), the porous layer width (0.2 ≤ 𝑊_p ≤ 0.8), the number of undulation (1≤ 𝑁 ≤ 4), and the nanoparticle volume fraction (0 ≤ 𝜙 ≤ 0.2). It is found that the inclination angle is a very influential control parameter for the hybrid nanofluid in the enclosure. Its effect is modulated by the other parameters. The model predicts that adding the nanoparticles enhances the heat transfer between the opposing walls of the cell compared to the pure fluid over the whole range of inclination angles. Finally, a comparison of the heat transfer enhancement based on the suspension of Al₂O₃ nanoparticles in water as a single nanofluid versus using Cu-Al₂O₃ nanoparticles in water as a hybrid nanofluid indicates better heat transfer performance by the hybrid nanofluid.