Influence of Porosity and Direction of Flow on Tortuosity in Unconsolidated Porous Media

Tortuosity tau is defined as the square of the ratio, phi-range of the effective length of pore channels to the length parallel to the overall direction of the pore channels in a porous medium. It has significance in interpreting the hydraulic and electric properties of porous media. In this study, experimental results of tortuosity and porosity phi were investigated in relation to different directions of flow in various unconsolidated porous media. When the media (mica, textile fibers, kaolinite, and bituminous soil, with a high phi-range of approximate to 60-90%) are exposed to flow perpendicular to the planes and fibers, tau responds positively to phi. When the media (randomly packed beds of spheres, with a medium phi-range of approximate to 34-45%) are exposed to flow parallel to the planes, tau responds negatively to phi. When the media (glass powders, glass spheres, dry soil, quartz sand, and white sand, with a variety of grain sizes and a medium porosity phi-range of approximate to 37-47%) and other media (glass spheres, with different fractions of grain sizes and a low phi-range of approximate to 10-30%) are exposed to nondirectional flow, tau responds negatively to phi. Empirical equations linking tau and phi, with medium to high coefficients of correlation, were obtained. The dependence of tau on phi is governed greatly by the direction of flow because of the orientation mineralogy, and mode of packing of the grains and nonuniformity in the size and shape of the grains and pores.