The critical thickness of a porous layer with respect to the porosity and its effect on heat transfer rate

Investigation of the thermal effects of a porous layer in an enclosure has not been studied completely in the literature and this challenge is generally considered to be an open research topic that may require more study. As the heat transfer rate in a vertical porous layer is higher than a horizontal layer, in this paper the effect of thickness of the vertical porous layer on natural convection in an enclosure is completely investigated using the lattice Boltzmann method. Therefore, after studying the effect of position of a porous layer on the Nusselt number, the effects of thickness of the porous medium on heat transfer rate are investigated. The obtained results show that a considerable amount of convective heat rate is transferred using the middle-vertical porous layer; and by increasing the thickness of the layer, the values of Nusselt number decrease which can be described by definition of the modified Rayleigh number. In addition, the critical thickness of the porous layer inside the cavity, (S/L)Crit. are reported in the moderate Rayleigh numbers for the first time.