Heat transfer enhancement with pressure drop optimisation in a horizontal porous channel locally heated from below

In this work, transient mixed convection heat transfer and fluid flow in a horizontal porous layer bounded by two impermeable plates with a localised heating from below is numerically studied. The study is conducted using the Brinkman–Forchheimer-extended Darcy model and the one-equation energy model based on the assumption of local thermal equilibrium. The effects of porosity (ɛ = 0.7−0.95) and permeability represented by Darcy number (Da = 0.1−100) are investigated for the following ranges of Richardson (Ri = 1−100) and Reynolds (Re = 0.1−50) numbers. The results show that the existence of the porous material increases Nusselt number, but does not change its trend with Reynolds number for all Richardson numbers. Interestingly, it is shown that unstable, oscillatory flow and temperature fields are generated in both empty and porous channels at higher Richardson number and/or higher Reynolds number. Also, both the heat transfer and the pressure drop are found to decrease as the porosity increases; however, the effect of Darcy number depends strongly on the range of Reynolds number.