This paper deals with a numerical investigation on natural convection heat transfer in a long horizontal annular region formed with a heated inner cylinder and a cooled outer cylinder. Identifying the annular region geometrically by its radius ratio, it is divided into two subregions: a thicker outer subregion is filled with a porous material saturated by air, whereas a thinner inner subregion is clear. Based on the general Darcy–Brinkman–Forchheimer model for flow in porous media, numerical calculations with the control volume method produce the velocity and temperature fields of the air motion in the two subregions. The baseline case corresponds to an annular region of same dimensions, but filled completely with a porous material saturated by air. Upon articulating the physical properties of a porous material with the clear gap size, the analyst will be able to tune those conditions that are conducive to heat transfer reduction across the concentric two-cylinder configuration. The outcome of this paper is equivalent to the determination of superior thermal insulation performance using lesser porous material. In other words, this paper boils down to beneficial energy conservation together with money savings in the purchase of the thermal insulation.
