A porous medium may be defined as a solid matrix containing holes either connected or non-connected, dispersed within the medium in regular or random manner provided such holes occur frequently in the medium. If these pores are saturated with a fluid, then the solid matrix with the fluid is called a fluid saturated porous medium. The flow of the fluid in a saturated porous material is possible only when some of the pores are interconnected. The interconnected pore space is termed as the effective pore space and the whole of the pore space is called the total pore space. If the package of the solid grains is regular, then it is called an ordered porous material, otherwise it is called a random porous material. Most natural and some of the artificial porous materials have random void structure. Natural porous media are ground soil, beach sand, rye bread, wood, human lung, etc., a few to quote. Porosity of a porous material is defined as the fraction of the bulk volume of the porous material occupied by pores. This gives the total porosity of the medium. But the effective porosity ϕ is defined as fraction of the bulk volume of the material occupied by the interconnected pores.