Setting Operating Density for Natural Convection when using Ideal Gas Law

How to set operating density for natural convection cases when density is modelled using ideal gas law?

Ansys Fluent software allows anisotropic thermal conductivity for solids but not for fluids. However, certain flows require accounting for non-isotropic thermal conductivity, for example due to the presence of disperse, oriented particles at molecular level. In such situations, it is possible to mimic this effect by introducing a porous media with no drag to modify the effective thermal conductivity.

The attached document describes how to setup a simulation to model air flowing through a channel with anisotropic thermal conductivity.