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The behavior of bubbles migrating in porous media is a critical factor in several soil remediation operations such as in situ air sparging, supersaturated water injection, bioslurping, trench aeration and up-flow operation of moving bed sand filters as well as in the oil and gas industry. Groundwater aquifers are constantly polluted by human activity and a common threat to fresh water is the contamination by non-aqueous phase liquids (NAPL). In many NAPL removal technologies, gas bubbles carrying NAPL residuals move upwards through the water-saturated porous media and thus play an essential role in contaminant recovery. The mobilization of the residual oil blobs in oil reservoirs is another important application for rising bubbles in porous media. After an oil field is waterflooded, a significant fraction of oil, referred to as waterflood residual oil, remains trapped. A potential mechanism to recover this residual oil is the mobilization of oil by gas bubbles moving upwards in water-wet systems. The main focus of this work was to measure the velocity of bubbles of various lengths during their migration through a water-wet porous medium. Experiments were conducted in a saturated glass micromodel with different test liquids, air bubbles of varying lengths and different micromodel elevation angles. More than a hundred experimental runs were performed to measure the migration velocity of bubbles as a function of wetting fluid properties, bubble length, and micromodel inclination angle. The results showed a linear dependency of the average bubble velocity as a function of bubble length and the sine of inclination angle of the model. Comparisons were made using experimental data for air bubbles rising in kerosene, Soltrol 170 and dyed White Oil. The calculated permeability of the micromodel was obtained for different systems assuming the effective length for viscous dissipation is equal to the initial bubble length. It was found that the calculated permeability had an increasing trend with increasing bubble length. Laboratory visualization experiments were conducted for air bubbles in White Oil (viscosity of 12 cP) to visualize the periodic nature of the flow of rising bubbles in a pore network. The motion of the air bubbles in saturated micromodel was video-recorded by a digital camera, reviewed and analyzed using PowerDVD ™11 software. An image of a bubble migrating in the porous medium was obtained by capturing a still frame at a specific time and was analyzed to determine the bubble shape, the exact positions of the bubble front and bubble tail during motion and, thus, the dynamic length of the bubble. A deformation in the shape of the bubble tail end was observed for long bubbles. The dynamic bubble lengths were larger than the static bubble lengths and showed an increasing trend when increasing the angle of inclination. The dynamic bubble lengths were used to recalculate the bubble velocity and permeability. A linear correlation was found for the average bubble velocity as a function of dynamic bubble length. Numerical simulation was performed by modifying an existing MATLAB® simulation for the rise velocity of a gas bubble and the induced pressure field while it migrates though porous media. The results showed that the rise velocity of a gas bubble is affected by the grid size of the pore network in the direction perpendicular to the bubble migration. In reality, this effect is demonstrated by the presence of other bubbles near the rising bubble in porous media. The simulation results showed good agreement with experimental data for long bubbles with high velocities. More work is required to improve the accuracy of simulation results for relatively large bubbles.

Commercial production and use of carbon-based nanomaterials will inevitably lead to the release of nanoscale compounds into to the environment. While fullerene nanoparticles, such as nC60 and multi-wall nanotubes (MWNTs), exhibit toxicity to certain microbes and human cell lines, their transport and deposition in subsurface environments are largely unknown. In this study, nanoparticle transport experiments were conducted in one-dimensional columns packed with water-saturated glass beads, quartz sands, or natural soil. Results demonstrated that nC60 transport was strongly influenced by electrolyte species and concentration, as well as mean grain size and flow rate. The attachment of nC60 was largely irreversible, with introduction of pH 12 water required to detach substantial quantities of retained nC60. Measured nC60 breakthrough curves and retention profiles in quartz sands suggest that the retention of nC60 was primarily due to attachment in a first energy minimum and that clean-bed filtration theory alone was not sufficient to describe the experimental data. In the presence of stabilizing agents, including surfactant, fulvic and humic acids, significant enhancement of nC60 transport in quartz sands was observed. In two natural soils, Appling and Webster soil, complete retention of nC60 was observed, even after introducing up to 65 pore volumes of nC60 suspension. However, nC60 readily transported through Appling soil in the presence of surfactant. For MWNTs with a manufacture-reported (MR) length of 50 μm readily transported through sand columns and the retention of MWNTs at higher input concentrations increased with the MR length. The data also suggested MWNTs exhibited higher mobility in quartz sands than nC60 or single-wall nanotubes under similar chemical conditions. These findings advance our current understanding of fundamental processes governing nanoparticle transport and retention in porous media and provide reliable experimental data for the development of nanoparticle transport models.

This thesis addresses modeling transport phenomena in porous media with special attention being paid to convective characteristics of variable viscosity fluids in a homogeneous and isotropic medium. Two different categories of flows, with totally different driving forces, are considered being forced and free convection (both side and bottom heating, for a square enclosure, are studied). To account for property variation, the density is modeled by an Oberbeck–Boussinesq approximation while the viscosity is modeled by an exponential function. The limitations of the previous work, addressing the issue, are discussed in detail and improvements, in terms of thermo-hydraulic performance of the system are suggested. Dealing with the global aspects of the problem, the two major methods being the reference temperature and the property ratio approach are implemented. For natural convection problems, the former method is used; while for forced convection the latter is undertaken. New correlations, which are proved to be more accurate, are proposed for both forced and free convection problems. Besides, closed form solutions are reported for some cases of constant and variable viscosity. Convection visualization is also studied in detail where the concept of Energy Flux Vectors is put forward along with the application of heatlines and energy streamlines. It was mathematically shown that in two-dimensional space heatlines and energy streamlines, which were invented independently, are the same as each other. Moreover, the newly developed concept, energy flux vectors serve as a new tool for convection visualization with the main advantage that this new technique, unlike heatlines and energy streamlines, does not require further (and sometimes complicated) numerical analysis in addition to solving momentum and thermal energy equations. This, in its turn, reduces the time and computer resources required to see the flow of energy. Finally, in Chapter 7, the summary of the work along with the conclusions are presented. Finally, recommendations for future studies are put forward.

This thesis addresses modeling transport phenomena in porous media with special attention being paid to convective characteristics of variable viscosity fluids in a homogeneous and isotropic medium. Two different categories of flows, with totally different driving forces, are considered being forced and free convection (both side and bottom heating, for a square enclosure, are studied). To account for property variation, the density is modeled by an Oberbeck–Boussinesq approximation while the viscosity is modeled by an exponential function. The limitations of the previous work, addressing the issue, are discussed in detail and improvements, in terms of thermo-hydraulic performance of the system are suggested. Dealing with the global aspects of the problem, the two major methods being the reference temperature and the property ratio approach are implemented. For natural convection problems, the former method is used; while for forced convection the latter is undertaken. New correlations, which are proved to be more accurate, are proposed for both forced and free convection problems. Besides, closed form solutions are reported for some cases of constant and variable viscosity. Convection visualization is also studied in detail where the concept of Energy Flux Vectors is put forward along with the application of heatlines and energy streamlines. It was mathematically shown that in two-dimensional space heatlines and energy streamlines, which were invented independently, are the same as each other. Moreover, the newly developed concept, energy flux vectors serve as a new tool for convection visualization with the main advantage that this new technique, unlike heatlines and energy streamlines, does not require further (and sometimes complicated) numerical analysis in addition to solving momentum and thermal energy equations. This, in its turn, reduces the time and computer resources required to see the flow of energy. Finally, in Chapter 7, the summary of the work along with the conclusions are presented. Finally, recommendations for future studies are put forward.