Porous Materials

A porous material (medium) is a substance that contains pores (voids), or spaces, between solid materials through which liquid or gas can flow. Examples of naturally occurring porous media include sand, soil, and some types of stone. Sponges, ceramics, and reticulated foam are also manufactured for porous materials. A porous material is characterized by its porosity, or the size of its pores. Materials with low porosity are less permeable and have smaller pores, making it more difficult for gas and/or liquid to flow through them.
It is natural to model porous materials as mixtures of a deformable solid and some fluids (gas, liquid). Also, the solid may be viewed as incompressible or compressible. With this in mind, the present approach to the modelling of porous materials is based directly on the theory of mixtures. Emphasis is given to the model consisting of a solid (skeletal material) and the remaining constituents as fluids. Next Darcy’s law is shown to follow by thermodynamic considerations if stationary conditions hold and the Darcy–Forchheimer equation is reviewed. Within the theory of mixtures special models are established: materials with voids, materials with double porosity, and materials with a thermoelastic solid.