Macroscopic behavior porous media

Characterization of porous media based on the pore (microscopic) level is carried out for the purpose of understanding, modeling, and sometimes controling the macroscopic behavior and properties of the medium. The macroscopic (bulk) properties needed to relate to the pore description are porosity, permeability, tortuosity, and connectivity. When one examines a sample of a porous medium, for example, sandstone, it is obvious that the number of pore sizes, shapes, orientations, and interconnections is enormous. Furthermore, even the identification of a pore is not unique. Because of this complexity, pore structure is often characterized based on an idealized model. A true description is not realistic for a natural porous medium. 

It is worthy to note that permeability as defined in Darcy s law (equation 13.1) pertains to the steady flow of fluid in a saturated porous medium, whereas the resin transfer process involves unsteady flow of resin into an unsaturated preform. The above holds true when analyzing the macroscopic flow through a fiber preform, i.e. flow in production of a composite part. However, one must be aware that the flow behavior in a fiber preform is markedly different when analyzed at the mesoscopic length scale, which concerns die interaction between the fluid and the intricate structure of the fiber bundles. 

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