Transport in Porous Media最新文献

This work investigates the dynamics of flow, transport and mixing in subsurface porous media during an engineered injection–extraction (EIE) system. We perform laboratory bench-scale experiments mimicking an EIE system in an unconfined aquifer, and we explore the role of local dispersion on mixing enhancement. The experimental setup is equipped with four wells operated in a sequence, one at a time, creating transient flows and a fluctuating water table impacting the transport dynamics of an injected dye tracer plume. A high-resolution imaging technique is applied to monitor the spatial and temporal evolution of the plume concentration. The experiments are performed in porous media with fine and coarse grain sizes and considering two different sequences of injection and extraction. The plume spreading and mixing are quantified by computing the spatial moments and the plume area, respectively. The Okubo–Weiss parameter is calculated over the plume area to correlate mixing enhancement with changes in flow topology. The results indicate that the operation of EIE system significantly enhances mixing and spreading, particularly when the effective Okubo–Weiss parameter is higher. Furthermore, the mixing enhancement is larger in the experiments performed in the coarse porous media, indicating the importance of local dispersion as a factor for mixing enhancement in EIE systems.

An analogy between magneto-fluid dynamics (MFD/MHD) in porous media and geostrophic flow in a rotating frame of reference in porous media including the existence of electromagnetic columns identical to Taylor-Proudman columns is identified and demonstrated theoretically. The latter occurs in the limit of small values of a dimensionless group representing the porous media Ekman number as well as even smaller values of an imposed magnetic field number. Consequently, the electromagnetic fluid flow subject to these conditions is two dimensional and the streamlines are being shown to be identical to the pressure lines in complete analogy to rotating geostrophic flows.

We demonstrate how to use pore-scale modeling combined with high-resolution imaging to make predictions of multiphase flow properties. Experiments were performed on two sandstone samples that were mixed-wet after contact with crude oil: Bentheimer and a reservoir rock. Flow experiments were combined with high-resolution X-ray imaging from which the pore space, fluid configurations and local contact angles can be measured. We first show that both lattice Boltzmann modeling and a pore network model can predict the fluid occupancy to within experimental and model uncertainty in Bentheimer using the measured contact angles. We then used the greater computational efficiency of the network model to simulate flow in a large network representing the reservoir sample. By calibrating the contact angle to match the observed pore-by-pore arrangement of fluid, the model was able to make predictions of relative permeability and capillary pressure that were within the bounds of experimental and model uncertainty. The results provide a framework for predictive image-based pore-scale modeling, where wet and dry images of rock samples are used to characterize both the pore structure and wettability.

The fundamental characteristic of a semi-permeable porous material is that the solvent is allowed to pass through it but the solute is not. Due to this characteristic, a solute concentration gradient can drive chemical osmosis flow in the solution-saturated semi-permeable porous material. Although analytical solutions have been derived for one-dimensional chemical osmosis induced flow and solute concentration variation problems, computational simulations of two-dimensional chemical osmosis induced flow and solute concentration variation problems remain lacking to date. To fill this gap, a new mathematical model is first established, in this paper, for describing two-dimensional chemical osmosis induced flow and solute concentration variation problems in solution-saturated semi-permeable porous materials. Then a computational simulation procedure, which contains the finite difference and finite element methods, is proposed to solve the partial differential equations involved in the established mathematical model. For the purpose of verifying the proposed computational simulation procedure, the analytical solution of a benchmark problem has been derived mathematically. The related computational simulation results have demonstrated that: (1) the proposed computational simulation procedure is correct and accurate for solving chemical osmosis induced flow and solute concentration variation problems; and (2) the applied boundary conditions have significant effects on the computational simulation results of two-dimensional chemical osmosis induced flow and solute concentration variation problems in the solution-saturated semi-permeable porous material.

Transport phenomena of complex fluids are investigated experimentally using laser-induced fluorescence combined with macroscopic pressure measurements. A comprehensive experimental methodology was developed in order to both capture as well as quantify global and local dynamics of involved flow phenomena, over a long period of time—technical features that constitute a significant experimental challenge. This methodology is adapted for a wide range of applications. The present paper shows a typical example of use that concerns the study of clogging issue, a subject of strong interest for several geoscience applications such as geothermal energy or CO₂ storage. More particularly this work aims to study the flow of colloids in a tortuous yet permeable 2D porous medium and the consequent clogging mechanisms in a rock-like microfluidic device. Indeed, previous microfluidic studies regarding this topic generally used porous media with very simple geometries (alignment of plots), thus failing to capture the tortuous nature of real porous media that significantly affects colloid transport and retention in porous media. The averaged deposit measurements determined by image analysis and the pressure drop measurements lead to very consistent results indicating a permeability reduction due to a progressive accumulation of deposit. Local observations make it possible to identify the preferential deposition sites, to describe the mechanisms and kinetics of clogging and hence to lead to a better interpretation of the macroscopic behavior. More precisely, results show that local and global dynamics may differ. When considering the entire porous medium, specific areas of the porous network are subjected to preferential accumulation of particles while others are not, suggesting that deposition is strongly influenced by tortuosity. At the pore scale, specific retention sites at the vicinity of grains are identified, and hydrodynamics effects such as stripping are highlighted. These observations emphasize the role of the porous medium geometry on colloidal transport.

The gas invasion mechanism through an initially saturated porous transport layer (PTL) of a proton exchange membrane (PEM) electrolysis is studied. Magnetic resonance imaging (MRI) technique is used to quantify water content in the porous layer during the gas invasion for different gas and water flow rates. Instead of the real PTL made of titanium which is paramagnetic and cannot be used in the MRI, borosilicate filters with thickness, porosity, and pore size similar to the PTL were used in the MRI experiments. The MRI measurement allows acquisition of the 2D water saturation map within the porous material, which can be averaged to obtain saturation profiles in the gas flow direction. The dependence of the saturation profile on the sample properties and the water/gas flow rates are carefully analyzed to give insight into the gas invasion pattern in such porous materials. Moreover, by recording the gas pressure at the inlet and observing the bubble formation and evacuation in the water channel, more information about the gas preferential pathways, bubble appearance sites can be achieved.

Many porous media are mixtures of inert and reactive materials, manifesting spatio-chemical heterogeneity. We study the evolution of scalar transport in a chemically heterogeneous material that mimics a green roof soil substrate, fractionally composed of inert and reactive adsorbing particles. These adsorbing particles are equivalent to biochar within a real soil substrate. The scalar transport evolution is determined using experiments and simulations calibrated from experimental data. Experiment 1 is used to determine the equilibrium capacity and adsorption rate of two biochar types when immersed in a methylene blue solution. Breakthrough curves of a packed bed of glass beads with randomly interspersed biochar are determined in experiment 2. Simulations are then run to investigate the solute transport and adsorption dynamics at the pore-scale. An analytical model is proposed to capture the behavior of the biochar adsorption capacity, and the simulation results are compared with experiment 2. A pore-scale analysis showed that uniformly sized beds are superior in contaminant breakthrough reduction, which is related to the adsorptive surface area and the rate at which adsorption capacity is reached. Cases using the adsorption capacity model display a tight distribution of particle surface concentration at later simulation times, indicating maximum possible adsorption. The beds with dissimilar particle sizes create more channeling effects which reduce adsorptive particle efficiency and consequently higher breakthrough concentration profiles. Comparison between experiments and simulations show good agreement. Improved biochar performance can be achieved by maintaining particle size uniformity alongside high adsorption capacity and adsorption rates appropriate to the rainfall intensity.

In this study, liquid jet impingement through porous metal foam-filled cooling channels with uniform cross sections and subject to a high heat flux value of 10⁵ W/m² is investigated numerically and several effective parameters are studied to achieve highly effective thermal control designs. The studied metal foam substrates are porous structures made of copper with porosity values of 0.45 and 0.86, and aluminum with the porosity value of 0.88. Three different jet inlet cross section shapes of rectangular slot, square, and circular are utilized in this work, while the jet flow rate for all cases is kept the same. To investigate the effect of jet size, three different circular jet diameters are modeled; one providing the same hydraulic diameter as that of the square jet, one indicating the same cross section area as that of the square case, and one representing a smaller jet cross section size. In addition, the effects of jet-to-target spacing and utilization of combined metal foam and conductive fins are studied. The comparisons are performed in terms of pressure drop, required pumping power, and nondimensional temperature profile and contour. The results indicate the advantage of utilizing copper foam with 0.86 porosity and circular jet impingement. Also, the local temperature can considerably be reduced when the combined foam and fin design is utilized. For hotspot treatment using combined foam and fin structure, the fin should be placed at the hotspot zone, right in front of the impinging jet. Among the studied fin-structured cases, the cross-shaped fin provides the most effective cooling without additional required pumping power.

The assessment of gas diffusion in water-saturated rocks is essential for quantifying gas loss and determining the amount of gas that could trigger abiotic and biotic processes, potentially altering fluid and rock properties. Additionally, estimating diffusion coefficients is critical for evaluating the balance between hydrogen generation and dissipation in radioactive waste repositories. This investigation involved experimental determination of diffusion coefficients for various gases both in water and in water-saturated Bentheim, Oberkirchner, Grey Weser, and Red Weser sandstones. Experimental conditions included pressures ranging from 0.2 to 1.0 MPa, consistently maintained at a temperature of 35 °C. The diffusion coefficients of hydrogen, helium, and methane in water were determined to be 6.7·10^–9, 9.6·10^–9, and 2.8·10^–9 m²/s, respectively, consistent with literature values obtained through gas concentration measurements without pressure gradients. However, the diffusivity of carbon dioxide and argon in water was measured at 10.9·10^–9 and 44.6·10^–9 m²/s, significantly exceeding their corresponding literature values by an order of magnitude. This discrepancy is attributed to the significant solubility of these gases in water, resulting in density-driven convection as the primary transport mechanism. Furthermore, the effective diffusion coefficients for hydrogen within the analyzed rock specimens varied from 0.8·10^–9 to 2.9·10^–9 m²/s, which are higher than those for methane and carbon dioxide, both ranging from 0.3·10^–9 to 0.9·10^–9 m²/s. This yielded diffusive tortuosity values ranging from 2.6 to 8.2. The observed effective diffusivity values were positively correlated with porosity, permeability, and mean pore size, while exhibiting a negative correlation with tortuosity. Given that the gas–liquid mass transfer coefficient is directly proportional to the effective gas diffusivity in water, the determined values for H₂ are essential for studying the impact of pore characteristics on microbial activity.

Media classification and the construction of pore network models from binary images of porous media hinges on accurately characterizing the pore space. We present a new method for (i) locating critical points, that is, pore body and throat centers, and (ii) partitioning of the pore space using information on the curvature of the distance map (DM) of the binary image. Specifically, we use the local maxima and minima of the determinant map of the Hessian matrix of the DM to locate the center of pore bodies and throats. The locating step provides structural information on the pore system, such as pore body and throat size distributions and the mean coordination number. The partitioning step is based on the eigenvalues of the Hessian, rather than the DM, to characterize the pore space using either watershed or medial-axis transforms. This strategy eliminates the common problem of saddle-induced over-partitioning shared by all traditional marker-based watershed methods and represents an alternative method to determine the skeleton of the pore space without the need for morphological reconstruction.