Impacts of variable porosity and variable permeability on the thermal augmentation of Cu–H2O nanofluid-drenched porous trapezoidal enclosure considering thermal nonequilibrium model

Our present work studies the impacts of variable porosity and variable permeability on the transient buoyancy-induced heat transmission flow of Cu–H ₂O nanofluid through a holey medium (glass bead, aluminum foam and sandstone) inside a right-angle trapezoidal cavity considering thermal nonequilibrium states amid the solid matrix and the nanofluid. We carried out numerical simulation by utilizing the Galerkin finite element method. We explored the impacts of the different model parameters on the thermal characteristics in details. The obtained numerical results confirm that the critical Rayleigh number, Ra _c, determining the thermal nonequilibrium state increased by increasing the Nield number, whereas it is found to be diminished with the increase in the diameter of the beads constructing the porous medium as well as with the porosity parameter. Additionally, the average Nusselt number in a porous medium having variable porosity is found to be higher compared to the medium of the uniform porosity. Increasing the variable porosity can significantly (more than 500%) increase the rate of heat transfer of the nanofluid in a porous medium. The higher porosity of the medium enhances the thermal state of a system to make it thermal nonequilibrium from the thermal equilibrium state. Furthermore, nanofluid flow in glass bead porous medium provides maximum (5% and 14% increase compared to the sandstone and aluminum foam, respectively) heat transmission rate.