![]() The larger the specific weight of a fluid ( γ = gρ) and the lower the dynamic viscosity ( μ), the higher the hydraulic conductivity. The specific weight and dynamic viscosity of the fluid also influence the hydraulic conductivity. Intrinsic permeability can also be computed if the hydraulic conductivity and fluid properties are known by rearranging Equation 31. In contrast, a porous material with small diameter pores and many circuitous interconnected pathways (high tortuosity) would have a lower intrinsic permeability. In general, the larger the diameter of the pores and the more efficiently they are interconnected (less tortuosity), the larger the intrinsic permeability. Tortuosity is a measure of actual distance traveled divided by the shortest distance between two locations. The intrinsic permeability represents the magnitude of variation in the diameters of the interconnected pores as well as the amount of branching and reconnecting of the pore pathways over a linear travel path, referred as the degree of tortuosity. Once the properties of the fluid are known, the hydraulic conductivity can be calculated from the intrinsic permeability as shown in Equation 31.įor sediments and rocks, intrinsic permeability ( k) incorporates the influence of all the media properties that affect flow, not only the mean grain diameter as was the case for the uniform glass spheres. Intrinsic permeability ( k) of the porous medium (L 2)Ī constant of proportionality representing effects of particle shape, tortuosity, and pore size distribution of the porous medium independent of fluid properties (dimensionless) When considered together with Darcy’s original observation that q ∝ − dh/ dl, these three relationships lead to a definition of hydraulic conductivity that includes physical characteristics of the porous media and the influence of fluid properties (Equation 30). Gravitational constant (acceleration of gravity) (L/T 2) Based on these observations, the relationship of the specific discharge to measurable characteristics of the porous media and were noted as shown in Equations 27, 28, and 29.ĭiameter of uniform glass beads comprising the porous medium (L) A number of columns filled with different sizes of glass beads were set up as Darcy columns and changes in specific discharge were observed. ![]() Intrinsic Permeabilityįreeze and Cherry (1979) describe the results of hydraulic conductivity experiments used to explore the relationship between physical properties of the porous media and the fluid. ![]() These conditions are also referred to as permeable or of low permeability, respectively. If water easily passes through a porous material it is described as having a high hydraulic conductivity if water is poorly transmitted through a material it has a low hydraulic conductivity. However, K is not a velocity, rather it represents the transmission properties of the porous material. Thus, the constant of proportionality, K, has units of velocity (e.g., meters/seconds, meters/day). In this configuration, it becomes clear that the units of K are L/T because Q units are (L 3/T), A units (L 2), h units are (L), and L units are (L). Rearranging Darcy’s law to solve for hydraulic conductivity generates Equation 25. It has direction and magnitude and is represented as a vector however, the first part of this discussion presents it as a scalar value. The hydraulic conductivity proportionality constant, K, can be conceptualized as the relative ease of fluid passage through a porous material.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |