Local Thermal Non-equilibrium Analysis of Cu-Al2O3 Hybrid ‎Nanofluid Natural Convection in a Partially Layered Porous ‎Enclosure with Wavy Walls

A numerical study is performed to investigate the local thermal non-equilibrium effects on the natural convection in a two-dimensional enclosure with horizontal wavy walls, layered by a porous medium, saturated by Cu-Al2O3/water hybrid nanofluid. It is examined the influence of the nanoparticle volume fraction, varied from 0 to 0.04, the Darcy number (10-5 ≤ Da ≤ 10-2), the modified conductivity ratio (0.1 ≤ ϒ ≤ 1000), the porous layer height (0 ≤ Hp ≤ 1), and the wavy wall wavenumber (1 ≤ N ≤ 5) on natural convection in the enclosure. Predictions of the steady incompressible flow and temperature fields are obtained by the Galerkin finite element method, using the Darcy-Brinkman model in the porous layer. These are validated against previous numerical and experimental studies. By resolving separately the temperature fields of the working fluid and of the porous matrix, the local thermal non-equilibrium model exposed hot and cold spot formation and mitigation mechanisms on the heated and cooled walls. By determining the convection cell strength, the Darcy number is the first rank controlling parameter on the heat transfer performance, followed by N, Hp and γ. The heat transfer rate through the hybrid nanofluid and solid phases is highest when N = 4 at a fixed value of nanoparticle volume fraction.