Browsing by Subject "Porous media"
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Item Open Access Geometry-Based Thermodynamic Homogenization for Porous Media, with Application to Resilience Prediction and Gyroscopic Sustainability(2021) Guevel, AlexandreUnderstanding and predicting the behavior of porous media holds unexpected potential for technological advances toward resilience and sustainability. Indeed, these materials are ubiquitous and exhibit a rich palette of processes, both multiphysics and multiscales, which are potential sources of inspiration for engineering design. Along these lines, the intended outcomes of this dissertation are twofold: 1) predicting the resilience of porous media and 2) enhancing behaviors of interest in these materials that could inspire sustainable metamaterials design. Geomaterials, a particularly complex subclass of porous media, will be the primary focus.
This program starts by laying down a general theoretical framework, based on non-equilibrium thermodynamics and differential geometry. A generalized relaxation equation is derived to ensure systematic satisfaction of the second law of thermodynamics. This is associated with a variational framework, based on Fermat's principle, that generalizes that of Onsager, in order to reckon with gyroscopic forces - that is, nondissipative but nonconservative forces.
This framework is then applied to modeling the microstructure of porous media, upon which the behavior of these materials largely depends. To that aim, phase-field modeling is employed to capturing the exact microstructural geometry, in association with digital rock physics based on microtomographic imaging. This effort is required to model processes too complex to be described by a unique constitutive law, such as pressure solution, as studied first in this dissertation. Therein, a microstructural viscosity is derived to capture the kinetics of processes, which is crucial for modeling geomaterials, since the associated timescales span from the engineering to the geological times.
Upon narrowing down the complexity of porous media processes, it is possible to extract the necessary and sufficient microstructural information through morphometry. From running phase-field simulations on a large variety of synthetic microstructures, a general morphometric strength law is inferred, which builds upon seminal works on metals and ceramics. This morphometric framework is applied to predicting the strength of various porous materials, including rocks and bones, from their microstructural geometry.
Item Open Access Investigating Linkages Between Engineering and Petrophysical Properties of Unconsolidated Geomaterials and Their Geoelectrical Parameters(2011) Owusu-Nimo, FrederickThe need for an improved ability to "see into the earth" has resulted in the use of geophysical techniques, especially the electrical resistivity method, in engineering and environmental investigations. The major challenge in the use of electrical resistivity measurements however is the interpretation of the electrical response. This is due to the lack of adequate understanding of the relationships between the physical factors controlling the engineering behavior of geomaterials (earth materials) and their measurable electrical parameters. This research work therefore sets out to investigate the linkages between engineering and petrophysical properties of geomaterials and their geoelectrical parameters. This goal is achieved through the development of laboratory equipments and the conduction of both laboratory and field studies. The laboratory experiments involve the measurement of the complex resistivity responses of natural and artificial soil samples under varying effective stress conditions. The field study involves the characterization of subsurface fracture parameters from field electrical measurements in complex fractured terrains at selected farming communities in Ghana.
The results from this study improve on our knowledge and understanding of the influence of fundamental engineering properties of geomaterials on their electrical responses. It results will aid in the interpretation of field electrical measurements and provide a means for engineering properties of geomaterials to be estimated from measurable electrical parameters. It will also contribute towards using non-invasive electrical measurements to locate weak zones in the subsurface, assess and monitor the stability conditions of soil units and assist in the environmental impact assessment of anthropogenic activities on groundwater resources in complex fractured terrain.
Item Open Access Nationalism and forgetfulness in the spreading of thermal sciences(International Journal of Thermal Sciences, 2021-05-01) Bejan, A© 2020 Elsevier Masson SAS This is a review of several key ideas and pioneers in the founding history of thermodynamics, fluid dynamics and heat transfer. Ideas treated in detail are the mechanical equivalent of heat, the difference between heat transfer and work transfer, the Navier-Stokes equations, natural convection in a fluid and a saturated porous medium, the gas bubble rising in a vertical tube filled with liquid, and fluid friction in duct flow. The review shows that good ideas spread and, at the same time the language and national preferences of the followers play a role in whether the idea creators are remembered or forgotten. The forgetting of the origin of ideas and their authors threatens to become a real problem during the digital era. This danger is exacerbated by the enormous increase in the number of publications most of which are not carefully reviewed or read.Item Embargo Pore-Scale Flow Mechanisms and the Hydrodynamic Porosity of Porous Media in Surface Water Treatment and Groundwater Remediation(2023) Frechette, AugustAs climate change and growing demand exacerbate water scarcity, it will become more imperative than ever to remediate our natural resources and treat our waste streams. This is especially true if we are to successfully provide clean water for all and ensure the future of endangered species and habitats. Thus, we look to surface water treatment technologies (e.g., granular media and filtration membranes) and groundwater remediation strategies (e.g., the vertical circulation well, rapidly pulsed pump and treat, and bioremediation) to add to our freshwater stores and reduce environmental pollution.
Complicating the matter is the fact that both surface water treatment and groundwater remediation are reliant, to varying degrees, on flow through porous media. Even without the added complexities of multiphase flows, immiscible fluids, and the time-dependent processes associated with chemical reactions and biofouling, characterizing flow through porous media, properly, is a cumbersome and arduous task. Heterogeneities in the morphology of the medium range from the pore scale, to, in the case of groundwater flows, meters. Resulting is a random distribution of the shape, size, and connectivity of the pore space. To quantify flow through porous media, researchers are forced to either make a set of simplifying assumptions, some more appropriate than others, or more recently, use black-box machine learning models that have little basis in the physicality of the flow. In this work, we choose to focus on one of the standard assumptions researchers make when calculating the pore-scale velocity (i.e., the supposed “static” nature of flow porosity). In relaxing this assumption, we provide a paradigm shift in the modeling of flows through porous media. We apply our theory to flow through and along the walls of microporous membranes, granular media, and aquifer substrates.
We choose to study pore-scale flow velocity because it is an essential parameter in determining transport through porous media, but it is often miscalculated. Researchers use a static porosity value to relate volumetric or superficial velocities to pore-scale flow velocities. We know this modeling assumption to be an oversimplification. The porosity conducive to flow, what we define as hydrodynamic porosity, exhibits a quantifiable dependence on Reynolds number (i.e., pore-scale flow velocity) in the laminar flow regime. This fact remains largely unacknowledged in the literature. In this work, we quantify the dependence of hydrodynamic porosity on Reynolds number via numerical flow simulation at the pore scale. We demonstrate that, for the tested flow geometries, hydrodynamic porosity decreases by as much as 42% over the laminar flow regime. Moreover, hydrodynamic porosity exhibits an exponential dependence on Reynolds number. The fit quality is effectively perfect, with a coefficient of determination of approximately 1 for each set of simulation data. We then demonstrate the applicability of this model by validating a high fit quality for a range of rectangular and non-rectangular cavity geometries. Finally, we show that this exponential dependence can be easily solved for pore-scale flow velocity using only a few Picard iterations, even with an initial guess that is over 10 orders of magnitude off. Not only is this relationship a more accurate definition of pore-scale flow velocity, but it is also a necessary modeling improvement that can be easily implemented.
In the chapters that follow our introduction of hydrodynamic porosity, we apply the concept to subsurface flow modeling for groundwater remediation via the vertical circulation well and flows over patterned membrane surfaces for surface water treatment – supposing that a hydrodynamic porosity parameter could be defined for the surface pattern of a membrane and then correlated to the rate of particle deposition (and therefore fouling) at the membrane surface.
In the future, we aim to explore the applicability of the hydrodynamic porosity model to microporous membrane wall flows. Although the characteristic length scale of the membrane wall is admittedly much smaller than the characteristic length scale of granular media, microporous membranes, like granular media, have dead-end pores. Thus, it remains necessary to determine the effect of these dead-end pore volumes on membrane wall flows. Preliminary experimental data previously collected from a hollow-fiber ultrafiltration membrane will be used to verify our numerical results.
Following our study of steady flows, we pivot to the analysis of rapidly pulsed flows and the mixing mechanisms these flows induce at the pore scale (i.e., the deep sweep and vortex ejection) in cavities and other effectively immobile zones. These mechanisms have been shown to significantly reduce contaminant recovery time in media with significant immobile zone volume. This finding suggests substantial cost-savings for treatment and remediation methods that utilize rapidly pulsed flows.
Regarding groundwater remediation, we estimate that the cost savings from utilizing rapidly pulsed flows could be on the order of magnitude of 100 billion USD. But this calculation assumes that we can remediate the entirety of a contaminated groundwater matrix with the mixing mechanisms induced by rapidly pulsed pump-and-treat. In application, induced oscillations will only reach a small volume of the flow field before dissipating to a negligible amplitude. Equally important, these oscillations will only induce a deep sweep or vortex ejection if the mean pore-scale flow velocity is above a Reynolds number of 0.1. Following, we use our model of hydrodynamic porosity to determine the magnitude of the volume we expect to benefit from rapidly pulsed pumping in a vertical circulation well.
Finally, given the similarity in characteristic length scale, we liken flow in the dead-end pore space of groundwater matrices, to flow past the channels in patterned membrane surfaces. We find that for the studied surface pattern, the vortex ejection and deep sweep are still present in highly laminar flows (i.e., a Reynolds number of 1600 for pipe flows). We hypothesize that these mechanisms can prevent particle deposition at the membrane surface, and when used as a cleaning mechanism, can remove loose deposits that would otherwise adhere to the membrane surface. It is also likely that these mechanisms would speed up the regeneration of fouled granular media used to remove suspended solids, microorganisms, and organics (i.e., sand and granulated activated carbon) from wastewater.
Item Open Access Reduced-order deep learning for flow dynamics. The interplay between deep learning and model reduction(Journal of Computational Physics, 2020-01) Wang, Min; Cheung, Siu Wun; Leung, Wing Tat; Chung, Eric T; Efendiev, Yalchin; Wheeler, Mary