ABSTRACT
This chapter describes general theories developed to explain resistance to flow through a porous media and the resistances of granular and fibrous packed beds are outlined as typical examples of high and low packing densities, respectively. Permeation is the fluid flow through interstices among many discrete particles. Flows of groundwater, crude oil, and natural gas are typical permeations taking place in nature. Porous media is composed of many discrete particles with different shapes and sizes. Porous media can be simplified as an assembly of many tiny channels or uniformly spaced spherical particles of equal size. A fibrous mat can be considered as a special kind of porous media composed of particles with an extremely large aspect ratio, to which both the channel and drag theories are applicable. The porosity of a fibrous mat is usually higher than 85%; thus, the average interfiber distance becomes larger than several times the fiber diameter.
