Flow control through the use of heterogeneous porous media: “Smart” passive thermo-insulating materials

In this paper, the concept of “smart” thermally insulating materials intelligently adapted to specific engineering configurations is established and extensively validated. Thermal insulation is achieved by local suppression of the momentum of the confined natural convection flow in the most critical regions, as determined by a linear stability analysis of the flow in the presence of implants of heterogeneous porous media. The implants are modelled by unconnected packed beds of equi-sized cylinders. The concept is based on a mesoscale approach in which the non-slip boundary conditions in the vicinity of the packed beds are explicitly imposed by utilizing the immersed boundary (IB) method. Two different patterns for the “smart” porous media are established, and their thermal insulation properties are quantified. It is shown that the optimized patterns for implants of heterogeneous porous media, occupying approximately only 5% of the overall volume, can drastically delay the steady-unsteady transition of the 2D natural convection flow in a square differentially heated cavity with thermally perfectly conducting horizontal walls. In addition, it is demonstrated that the implants facilitate a consistent decrease in the heat flux through a cubic differentially heated cavity with all being thermally perfectly conducting lateral walls.