Three-dimensional Pore-scale Visualization and Trajectory Analysis of Colloid Transport and Retention in Saturated Porous Media PDF Download
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Author:
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ISBN: 9781109393491
Category : Colloids
Languages : en
Pages :
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Book Description
The research contained in this thesis investigates the transport and deposition behavior of 1.1 and 3ìm carboxylate-modified microspheres in saturated porous media under unfavorable deposition conditions. Colloid motion and deposition patterns are visualized in three dimensions using a high-speed confocal microscope and micromodels packed with glass beads or sand grains. This study specifically focuses on colloid behavior in the grain-to-grain contact region, which has been suggested in previous studies as an important location for colloid retention under unfavorable conditions. The use of the high resolution confocal microscope allowed the distinction of two types of colloidal retention that can occur in the grain-to-grain contact region and showed that single surface retention was much more abundant than retention on two surfaces (straining). This study also demonstrated that both the extent and rate of straining are enhanced by increasing flow rate. In addition to obtaining qualitative descriptions of colloid deposition patterns, this study is the first to provide quantitative analysis of the motion of individual colloidal particles leading to the construction of three-dimensional colloid trajectory in both the bulk phase and grain-to-grain contact regions. The results demonstrated the dominant effects of hydrodynamics on colloid motions, i.e., most colloids entering the grain-to-grain contact region tend to follow the streamlines to detour the contact point, making straining a transport-limited process. Retention in the secondary energy minimum can significantly retard colloid movement but this association was not strong enough to keep the retained colloid inside the energy well over time. Colloid retention and movement through sand-packed sand micromodels were more complex compared to those packed with glass beads due to the more complex hydrodynamic conditions resulting from the irregular packing geometry and surface roughness of sand. These results suggest that theoretical torque analysis based on the idealized scenarios is not a suitable approach for describing colloid transport and deposition under unfavorable conditions in complex natural porous media.
Author:
Publisher:
ISBN: 9781109393491
Category : Colloids
Languages : en
Pages :
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Book Description
The research contained in this thesis investigates the transport and deposition behavior of 1.1 and 3ìm carboxylate-modified microspheres in saturated porous media under unfavorable deposition conditions. Colloid motion and deposition patterns are visualized in three dimensions using a high-speed confocal microscope and micromodels packed with glass beads or sand grains. This study specifically focuses on colloid behavior in the grain-to-grain contact region, which has been suggested in previous studies as an important location for colloid retention under unfavorable conditions. The use of the high resolution confocal microscope allowed the distinction of two types of colloidal retention that can occur in the grain-to-grain contact region and showed that single surface retention was much more abundant than retention on two surfaces (straining). This study also demonstrated that both the extent and rate of straining are enhanced by increasing flow rate. In addition to obtaining qualitative descriptions of colloid deposition patterns, this study is the first to provide quantitative analysis of the motion of individual colloidal particles leading to the construction of three-dimensional colloid trajectory in both the bulk phase and grain-to-grain contact regions. The results demonstrated the dominant effects of hydrodynamics on colloid motions, i.e., most colloids entering the grain-to-grain contact region tend to follow the streamlines to detour the contact point, making straining a transport-limited process. Retention in the secondary energy minimum can significantly retard colloid movement but this association was not strong enough to keep the retained colloid inside the energy well over time. Colloid retention and movement through sand-packed sand micromodels were more complex compared to those packed with glass beads due to the more complex hydrodynamic conditions resulting from the irregular packing geometry and surface roughness of sand. These results suggest that theoretical torque analysis based on the idealized scenarios is not a suitable approach for describing colloid transport and deposition under unfavorable conditions in complex natural porous media.
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Category :
Languages : en
Pages :
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Book Description
The recent study by Crist et al. (2004) attempted to provide pore scale insights into mechanisms responsible for controlling colloid transport in unsaturated porous media. However, because they relied on images obtained along surfaces that were open to the atmosphere, artificial evaporation resulted in 2 more critical artifacts; formation of air-water-solid (AWS) contact lines, and advection/deposition of colloids to AWS contact lines. These evaporation-related artifacts need to be addressed because they account for most of the colloid deposition at AWS contact lines reported in Crist et al. (2004) ... As stated in Crist el al. (2004), '' ... the front panel was removed to avoid light reflections that obscured the view and, thus, exposed one side of the sand column to air''. Although a more recent paper (Crist et al., 2005) also presents results using the same methods and is therefore also affected by evaporation, we will restrict our present comments to Crist et al. (2004). Here, we show that removal of the front panel results in a sequence of three critical artifacts; (1) significant evaporation, (2) drying of thin films and formation of air-water-solid (AWS) contact lines, and (3) advection of colloids to AWS contact lines where they are deposited. As explained below, these artifacts so drastically disturbed their system that the magnitude of their observations are not likely to occur anywhere except within the most superficial few cm of soils. Before explaining these artifacts, we note that although trapping of colloids at AWS contact lines reported in Crist et al. (2004) is largely an artifact of evaporation, colloid filtration within perimeters of pendular rings is in fact a main prediction of the film straining model (Wan and Tokunaga, 1997). In that model, colloid filtration is predicted to be more efficient below a critical water saturation, when capillary connections between pendular rings become separated by adsorbed water films. In that paper we stated that ''Retardation of ideal, nonsorbing colloids can occur at two locations: trapped within individual pendular rings due to exclusion from entry into surrounding thin films and within film ... '' (Wan and Tokunaga, 1997). Thus, while Crist et al. (2004) implied that the film straining model applies only to retardation of colloid transport within thin films, colloid retention within perimeters of pendular rings is a main feature of our model.
Author: Wael Ahmed
Publisher: BoD – Books on Demand
ISBN: 953510778X
Category : Technology & Engineering
Languages : en
Pages : 250
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Book Description
The serious challenge facing the world today, in obtaining enough energy for growing population and in controlling the carbon emission caused by fossil fuel use, calls for nuclear energy as an alternative power source. This book presents research work and technical experience from several power plants and research institutions around the world from practical prospective. This book intends to provide useful information for scientists and those in technical fields in several areas in nuclear power plants including: nuclear systems protection, design and modelling of critical parameters in nuclear power plants, thermalhydraulic analysis, nuclear waste management and safety and reliability assessment.
Author: John T. Crist
Publisher:
ISBN:
Category :
Languages : en
Pages : 154
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Book Description
Author: Jennifer Smith
Publisher:
ISBN:
Category :
Languages : en
Pages : 136
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Book Description
Author: Yuniati Zevi
Publisher:
ISBN:
Category :
Languages : en
Pages : 122
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Book Description
Author: Swatantra P. Singh
Publisher: Springer Nature
ISBN: 9811683670
Category : Science
Languages : en
Pages : 623
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Book Description
This book is based on recent trends for the research in emerging environmental contaminants in different compartment of the environment. It provides a recent understanding for the fate, transport, and degradation of emerging contaminants in different environmental sectors, including water, air, and soil. The contents discuss the fate and transport of microplastics, PPCPs, along with the method of detection and degradation. It includes removal of variety of pollutants including microplastics, pharmaceuticals, and personal care products from the water using adsorption technique, electrooxidation, membrane technology and other advance oxidation methods. This volume will be of great value to those in academia and industry involved in environmental science and engineering research.
Author: Hongjuan Bai
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
The investigation of the transport and retention of bacteria in porous media has a great practical importance in environmental applications, such as protection of the surface and groundwater supplies from contamination, risk assessment from microorganisms in groundwater, and soil bioremediation. The aim of this study is to gain a fundamental understanding of the mechanisms that control bacteria transport and deposition in saturated and unsaturated porous media. Laboratory tracer and bacteria transport experiments at Darcy scale were performed in three porous media with distinct pore size distribution in order to investigate and quantify water and bacteria transport process under steady state flow conditions. A conservative solute was used as water tracer to characterize water flow pathways through porous media. A gram negative, motile Escherichia coli, a gram negative, non-motile Klebsiella sp. and a gram positive, non-motile R. rhodochrous were selected for the transport experiments. Characterization of cell properties (such as cell size and shape, zeta potential, motility and hydrophobicity) was performed for each strain. Numerical simulations with HYDRUS-1D code were performed to characterize water flow and to estimate bacteria transport and deposition parameters. The later were explored to identify bacteria flow patterns and physicochemical or physical mechanisms involved in bacteria deposition. To provide a better understanding of the mechanisms involved on bacteria transport and deposition, pore scale experiments were carried out by using microfluidic devices, designed for this purpose. The information obtained from laboratory experiments and numerical modeling was improved by theoretical calculation of different interactions between bacteria and porous media at air/water/solid interfaces. DLVO and non-DLVO interactions such as hydrophobic, steric, capillary and hydrodynamic forces involved in bacteria deposition were considered to describe bacteria-interface interactions in order to identify their relative impact on physicochemical and physical deposition of bacteria. Results obtained through both laboratory experiments and numerical simulationsoutlined non-uniform flow pathways, which were dependent on both grain/pore size as well as pore size distribution of the porous media. For a given porous medium, water flow patterns became more non-uniform and dispersive with decreasing water saturation due to the presence of air phase, which lead to an increase of the tortuosity of the flow pathways under unsaturated conditions. Bacteria transport pathways were different from the tracer transport, due to size exclusion of bacteria from smaller pore spaces and bacteria motility. Bacteria deposition was greatly influenced by pore network geometry, cell properties and water saturation degree. Both physical straining and physicochemical attachment should be taken into account to well describe bacteria deposition, but their importance on bacteria deposition is closely linked to porous media and cell properties. The results obtained in this work highlighted the simultaneous role of cell properties, pore size distribution and hydrodynamics of the porous media on bacteria transport and deposition mechanisms. The calculation of DLVO and non-DLVO interactions showed that bacteria deposition in saturated and unsaturated porous media was influenced by both kinds of interactions.
Author: F Dullien
Publisher: Elsevier
ISBN: 0323151353
Category : Technology & Engineering
Languages : en
Pages : 417
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Book Description
Porous Media: Fluid Transport and Pore Structure presents relevant data on the role of pore structure in terms of transport phenomena in pore spaces. The information is then applied to the interpretation of various experiments and results of model calculations. This book emphasizes the discussion of ""flow through porous media"" in terms of interactions among the three main factors. These factors are transport phenomena, interfacial effects, and pore structure. An introductory chapter opens the text and presents some of the basic concepts and terms that will be encountered all throughout. Chapters 2 to 4 focus on the important foundations of the physical phenomena as applied in the pore space of porous media. These foundations are capillarity, pore structure, and single phase flow and diffusion. Chapters 5 to 7 discuss more in detail the different applications of pore structure to various operations and processes. Some of the concepts covered in this part of the book include flow and/or diffusion through a porous medium, simultaneous flow of immiscible fluids and immiscible displacement, and miscible displacement and hydrodynamic dispersion. This book is a good reference to students, scientists, and engineers in the field of chemistry, physics, and biology.
Author:
Publisher:
ISBN: 9780549925293
Category : Colloids
Languages : en
Pages :
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Book Description
Colloid-facilitated transport of contaminants and transport of biocolloids (e.g., viruses and bacteria) in soil porous media are acknowledged environmental issues. Understanding of the mechanisms and parameters controlling colloid transport is important for protection of soil and groundwater resources from bio- and chemical contamination and improvement of remediation practices. For research purposes, unsaturated soil is often represented with idealized porous media, which facilitates conceptual understanding of colloid transport and retention mechanisms. Major colloid retention mechanisms include retention at solid-water interface (SWI), at air-water interface (AWI), and on the contact line. Additional colloid retention occurs as a result of straining in the narrow, compared to colloid size, regions of porous media. Colloid retention at AWI and colloid retention on the contact line are characteristic of unsaturated porous media and are currently associated with substantial uncertainty in colloid transport literature regarding their respective roles and contributions to overall colloid retention. In order to distinguish colloid retention mechanisms, traditional laboratory column experiments often require supplementary pore-scale investigation. The focus of this research was to investigate colloid retention at AWI and contact line at the pore scale. In this work, open capillary channels and microfluidic channels were utilized as models of soil capillaries, and behavior of colloids was visualized directly with confocal microscope. The employed channels have angular cross sections, which is in agreement with a more realistic angular representation of soil capillaries. The open-channel configuration served as a model of free-surface flow in microscopic grooves and corners in soil while the microfluidic channels were used to represent two-phase (air-water) flow in soil such as during drainage and infiltration events. To acquire qualitative and quantitative information, experimental confocal images were recorded and systematically processed with advanced imaging software. Colloid behavior in open channels with square cross section was investigated both in static and dynamic regimes. During flow in the channel, colloid movement occurred along the contact line, which acted as a colloid accumulation site due to reduced velocities in the contact line region. For this channel configuration, flow stagnation at AWI was observed, which promoted colloid retention at AWI. The maximum velocity and therefore maximum colloid transport were observed inside the channel. These observations indicated the importance of hydrodynamic conditions in affecting colloid retention. In the static regime, effects of a number of physicochemical parameters on colloid retention at AWI, including ionic strength, colloid contact angle, and surface tension (addition of surfactant), were investigated. It was shown that retention of colloids at AWI was dependent on electrostatic conditions and colloid contact angle and varied to a lesser extent with addition of non-ionic surfactant. The retention of colloids at AWI in a static system was analyzed with extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and was attributed to a possible secondary energy minimum retention. In microfluidic channels, which have a trapezoid cross section, AWI was observed as a two-phase boundary. In such configuration, both AWI and contact line move in the flow direction. It was shown that colloid retention on the contact line was considerably affected by hydrodynamic conditions. Colloid retention at AWI occurred primarily via involvement of colloids, which were previously deposited on the wall, with the moving contact line. Direct retention of dispersed colloids at AWI was not observed. The moving AWI was realized both as receding (air) and advancing (water) fronts, which allowed examination of the role that AWI played in colloid mobilization under both drainage and infiltration scenarios. Experimental results were considered in view of colloid interaction energies as well as forces acting on colloids at the sites of interest. Both experimental and theoretical findings resulted in improved understanding of colloid retention at AWI and contact line in the considered configurations, i.e., open channel and two-phase flows. The results of this research provide mechanistic understanding of colloid retention and can be applied in interpretation of observations at larger scales and in modeling of colloid transport in unsaturated porous media. This dissertation is accompanied with supplementary material showing representative video images and illustrating the discussed processes. System requirements for viewing the video: Windows Media Player or RealPlayer.
