Abstract
The application of 3D technology for fabrication of artificial porous media samples improves porous media flow studies. The geometrical characteristics of a porous media pore channel: the channel shape, size, porosity, specific surface, expansion ratio, contraction ratio, and the tortuous pathway of the channel can be controlled through advanced additive manufacturing techniques (3D printing), computed tomography imagery (CT imaging) and image analysis methods. These 3D technologies have here been applied to construct and analyze four homogeneous porous media samples with predefined geometrical properties that are otherwise impossible to construct with conventional methods. Uncertainties regarding the geometrical properties are minimized because the 3D-printed porous media samples can be evaluated with CT imaging after fabrication. It is this combination of 3D technology that improves the data acquisition and data interpretation and contributes to new insight into the phenomenon of fluid flow through porous media. The effects of the individual geometrical properties on the fluid flow are then accounted for in permeability experiments in a Hassler flow cell. The results of the experimental work are used to test the theoretical foundation of the Kozeny–Carman equation and the extended version known as the Ergun equation. These equations are developed from analogies to the Hagen–Poiseuille flow equation. Based on the results from the laboratory experiments in this study, an analytical equation based on the analytical Navier–Stokes equations is presented as an alternative to the Hagen–Poiseuille analogy for porous media channels with non-uniform channel geometries. The agreement between experiment and the new equation reveals that the dissipating losses of mechanical energy in porous media flows are not a result of frictional shear alone. The mechanical losses are also a result of pressure dissipation that arise due to the non-uniformity of the channel geometry, which induced spatial variations to the strain rate field and induce acceleration of the velocity field in the flow through the porous medium. It is this acceleration that causes a divergence from linear flow conditions as the Stokes flow criterion (Re ≪ 1) is breached and causes the convective acceleration term to affect the flow behavior. The suggested modifications of theory and the presented experiments prove that the effects of surface roughness (1) do not alter the flow behavior in the Darcy flow regime or (2) in the Forchheimer flow regime. This implies that the flow is still laminar for the Forchheimer flow velocities tested.
Highlights
Fluid flow through a porous media is a subject of global interest and a topic of extensive research within fields of scientific and industrial nature alike
The presented experiments demonstrate that the application of additive manufacturing (AM), CT imaging, and image analysis techniques represents an improvement in porous media studies
These 3D technologies enable the study of porous media in a controlled fashion and allow experimental testing on geometries that would otherwise be impossible to achieve with conventional study methods on natural soils or particle beds
Summary
Fluid flow through a porous media is a subject of global interest and a topic of extensive research within fields of scientific and industrial nature alike. Within the field of civil engineering, e.g., drinking water supply, water resource management, groundwater heat pump systems, coastal erosion, and water contamination there frequently exists a need to determine the rate of groundwater flow through soil formations. Occurring soil formations have a potential for large spatial variation, and this often requires the determination of a large number of local hydraulic conductivities to adequately describe the over-all field K for an aquifer. Many engineering projects do not have the budget to perform time-consuming and costly field or laboratory permeability tests. Simple predictive methods that estimate the hydraulic conductivity from individual soil samples are still a common and valued approach in the industry
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