Transport in Porous Media最新文献

We investigate two-phase flow in porous media and derive a two-scale model, which incorporates pore-scale phase distribution and surface tension into the effective behavior at the larger Darcy scale. The free-boundary problem at the pore scale is modeled using a diffuse interface approach in the form of a coupled Allen–Cahn Navier–Stokes system with an additional momentum flux due to surface tension forces. Using periodic homogenization and formal asymptotic expansions, a two-scale model with cell problems for phase evolution and velocity contributions is derived. We investigate the computed effective parameters and their relation to the saturation for different fluid distributions, in comparison to commonly used relative permeability saturation curves. The two-scale model yields non-monotone relations for relative permeability and saturation. The strong dependence on local fluid distribution and effects captured by the cell problems highlights the importance of incorporating pore-scale information into the macro-scale equations.

This study examines the simultaneous impact of temperature-dependent viscosity and Robin boundary conditions on velocity, focusing on analyzing the stability of buoyant parallel flow in a differentially heated vertical porous layer. The neutral stability condition and the instability thresholds are determined numerically for various values of governing parameters. The onset of instability of the base flow is accurately analyzed by introducing a non-negative parameter that measures the extent of departure of boundaries from impermeable to permeable. It is established that the base flow becomes unstable when this parameter exceeds a threshold value, which significantly depends on the variable viscosity parameter. This work demonstrates a clear bridge between impermeable and permeable boundaries in the context of a variable viscosity fluid.

Migration of variably sized fines or geogenic colloids is a significant concern for the long-term efficiency of aquifer management and reservoir injection and extraction operations. Characterizing the migration of colloids in porous media has been widely studied; however, few studies have quantified sub-core colloidal transport behavior and related this to bulk sample observations under transient conditions. In this study, the transport of colloidal kaolinite through sand packs is analyzed using UV–Vis spectrophotometry and positron emission tomography (PET). PET imaging was completed by imaging an aqueous pulse of suspended radiolabeled kaolinite under single-phase flow conditions. The experimental PET imaging approach allows for the accurate 4-D quantification of changes in colloidal kaolinite transport, attachment, and detachment properties at the sub-centimeter scale. This study provides a novel approach for the quantification of inorganic colloid transport in geologic porous media, providing a foundation for future work to be done on more complex and heterogeneous systems under transient flow and fluid chemistry conditions.

Reliable reactive transport models require careful separation of mixing and dispersion processes. Here we treat displacing and displaced fluids as two separate fluid phases and invoke Whitman’s classical two-film theory to model mass transfer between the two phases. We use experimental data from Gramling’s bimolecular reaction experiment to assess model performance. Gramling’s original model involved just three coupled PDEs. In this context, our new formulation leads to a set of seven coupled PDEs but only requires the specification of two extra parameters, associated with the mass transfer coefficient and its dependence on time. The two film mass transfer model provides a simple and theoretically based method for separating mixing from dispersion in Eulerian continuum-scale methods. The advantage of this approach over existing methods is that it enables the simulation of equilibrium chemical reactions without having to invoke unrealistically small reaction rate coefficients. The comparison with Gramling’s experimental data confirms that our proposed method is suitable for simulating realistic and complicated bimolecular reaction behaviour. However, further work is needed to explore alternative methods for avoiding the need of a time-dependent mass transfer rate coefficient.

Visualising fluid flow in porous media using optical techniques is challenging due to the inability to see through the medium. Here, we present an experimental methodology based on shadowgraphy to investigate the dynamic spreading of convective plumes in saturated transparent porous media made of glass beads. The saturated porous medium can be tuned transparent by matching the refractive index of the solid glass beads to that of the saturating fluid mixture. The proposed technique allows to investigate the essential elements of convective mixing within a porous medium using miscible fluids. We also describe a method to determine the velocity of convective plumes as they propagate. Our experimental results show that the density difference achieved during convection significantly affects the convective front velocity of the plumes. This is significant because it allows to quantitatively predict the intensity of convective mixing in porous media from the speed of the convective front.

Additive manufacturing (AM) allows the production of the internal structure of porous media (PM) with porosity and permeability tailored for a specific application. Material extrusion (MEX) AM enables the fabrication of a lattice-type porous structure by varying process parameters, usually applying the zigzag raster filling strategy. In a recent study, a Variable Bead Width Porous Filling (VBWPF) strategy was proposed, which generates pores by changing the printing speed during filament deposition and resulting in a unique porous structure with less pore interconnectivity. Specific pores’ dimensions and distribution on the layer can be obtained with the strategy’s parameters. In this work, different configurations of the VBWPF strategy were produced, and their porosity and permeability were measured experimentally. A PM with traditional raster filling (lattice structure) was also printed and measured for comparison. The porous structures of different VBWPF configurations were analyzed with micro-computed tomography (µCT). The results showed that VBWPF parameters were able to modify the porous structure obtained, changing the porosity and permeability of the PM. The PM produced exhibited 27% lower porosity and 55% lower permeability than the traditional raster filling PM with similar pore widths. These unique characteristics open up the field for applications of PM obtained through AM.

The mechanism of fluid and heat transmission within materials with complex porous structures has not yet been fully explored and understood using basic analytical techniques. Therefore, the lack of advanced equipment and techniques has left an important knowledge gap in explaining the complex mechanisms of fluid motion and heat transfer in complex porous structures. This review provides an overview of how image analysis and processing techniques allow insight into the complex and heterogeneous porous structure of materials and explains the mechanism of heat and mass transfer in these complex porous materials in 3D and 4D observation in different directions. Accordingly, it provides interesting results related to the evaluation of microporous properties of complex porous materials including porosity, distribution and size of pores, distribution and orientation of fibers, tortuosity and mechanism of cracking, and destruction of the porous materials under mechanical tests. It also explains the mechanism of liquid transport in porous materials through 3D/4D observation thanks to image processing techniques. Therefore, this review has completed some limited knowledge in microstructural analysis and helped to understand the physical phenomena of liquid transfer in complex porous materials that were not fully exploited by experimental or simulation work. The paper also provides useful data for physical model simulation of imbibition and drying porous materials.