Percolation In Porous Media Research Articles

Numerical simulation of gas-water two-phase seepage flow based on level set method

The mechanism of gas-water two-phase percolation was previously characterized based on percolation experiments. However, the changes in the gas-water interface and the volume fraction of the two phases in the process of gas-water percolation in porous media cannot be accurately described by experiments. This paper uses core casting thin sections and AutoCAD software to establish a digital core. Based on the idea of level set, a two-dimensional gas-water seepage model in microscopic pores is established. The finite element numerical simulation software is used to solve the model to describe the gas. The changes of the water two-phase interface are visually displayed. At the same time, Darcy’s law is used to compare the relative permeability curve obtained from the gas-water two-phase seepage experiment with the relative permeability curve obtained from the gas-water two-phase seepage finite element simulation. The results show that the gas-water two-phase seepage experiment and the gas-water two-phase seepage finite element numerical simulation have basically the same characterization of the seepage ability of porous media. There is obvious fingering phenomenon in the process of gas flooding, and the gas preferentially passes through the large pore throat. The smaller the pore throat, the greater the velocity of gas passing through the pore throat. The gas-water two-phase interface change described by the numerical simulation of the gas-water two-phase flow based on the digital core is more reliable.

DRYWELLS DIMENSIONING: ANALOGY BETWEEN WATER FLOW IN SOIL AND HEAT FLUX IN MEDIA SOLIDS

The drywell is an on-lot drainage system, which is composed by an excavation in the soil lined with a perforated piped and gravel at the bottom and sides. There are many models for on lot systems dimensioning, which were initially developed for agriculture areas or for simulation of water percolation in porous media, thus, they are not fully optimized for small areas like urban lots. This article proposes a model for dimensioning drywells, which is based on physical and hydrological characteristics of the installation site. It was developed using the analogy between water flow in soil and the heat flux in media solids. Results obtained with the proposed model were statistically similar (p>0,05) to those obtained with experimental data.

A Quantitative Technique to Compare Experimental Observations and Numerical Simulations of Percolation in Thin Porous Materials

Quantitative validation of numerical simulations of percolation in porous media has always been challenging due to the stochastic nature of the material structure and morphology regardless of the numerical technique being used. In this article, we present a technique that allows for a quantitative comparison between numerical and experimental percolation. The experimental observations are of injection pressure and liquid intrusion within thin porous materials in a Hele-Shaw style test. The thin porous materials tested had a surface treatment such the contact angle was larger than \(90^{\circ }\) resulting drainage percolation. Flow rates were adjusted to encompass the range of capillary numbers for drainage flow patterns between the stable displacement and capillary fingering. In parallel to the experimental observations, a series of numerical simulations using a two-dimensional pore network model were performed mimicking the Hele-Shaw experiments. The material properties of the pore network realizations, pore size distribution, contact angle, and representative volume for the pore space were based on measurements of the porous materials tested. Boundary and initial conditions were matched between numerical simulations and experiments. To compare and validate the numerical simulation against the experiments, a new scaling of the dissipated energy during percolation in thin porous media was used. This scaling has been recently used to identify the transition between capillary fingering and stable displacement for drainage in different thin porous materials and provides a unique method for characterizing percolation in thin porous materials. Though the experiments and simulations presented in this article are for drainage, the technique described is equally applicable to imbibition. Excellent agreement is obtained between experiment and simulation with clear delineation between different types of thin porous materials.

Scaling percolation in thin porous layers

Percolation in porous media is a complex process that depends on the flow rate, material, and fluids properties as well as the boundary conditions. Traditional methods of characterizing percolation rely upon visual observation of a flow pattern or a pressure-saturation relation valid only in the limit of no flow. In this paper, the dynamics of fluid percolation in thin porous media is approached through a new scaling. This new scaling in conjunction with the capillary number and the viscosity ratio has resulted in a linear non-dimensional correlation of the percolation pressure and wetted area in time unique to each porous media. The effect of different percolation flow patterns on the dynamic pressure-saturation relation can be condensed into a linear correlation using this scaling. The general trend and implications of the scaling have been analyzed using an analytical model of a fluid percolating between two parallel plates and by experimental testing on thin porous media. Cathode porous transport layers (PTLs), also known as gas diffusion layers, of a proton exchange membrane (PEM) fuel cell having different morphological and wetting properties were tested under drainage conditions. Images of the fluid percolation evolution and the percolation pressure in the PTLs were simultaneously recorded. A unique linear correlation is obtained for each type of PTL samples using the new scaling. The correlation derived from this new scaling can be used to quantitatively characterize porous media with respect to percolation. While the characterization method discussed herein was developed for the study of porous materials used in PEM fuel cells, the method and scaling are applicable to any porous media.

Comparison of Numerical Predictions and Experimental Results of Water Percolation in PEM Fuel Cell Porous Transport Layers

A series of numerical simulation using a three dimensional version of the network model are presented. These numerical simulations are carried on in similar conditions occurring during a pseudo Hele-Shaw experimental setup. The numerical simulations using the network model are compared with experimental data through a new scaling of the water percolation in porous media which is based on the ratio dissipated energy. The morphology and wettability of the PTL are tuned to fitting the experiment by using the proposed scaling. Once the fitting between numerical and experimentally is obtained, such PTL structure information can be used in different types of simulations where the conditions are representative of the fuel cell operating conditions.

A model for enhanced fluid percolation in porous media by application of low‐frequency elastic waves

Numerous observations and laboratory experiments suggest that elastic vibrations can significantly enhance transport of nonaqueous phase liquids (NAPLs) in porous media. Our analyses suggest that in the low‐frequency range, capillary forces and nonlinear rheology of the fluid may be predominant mechanisms of vibratory stimulation. Consequently, a model of these mechanisms is built to explain the effect of sonic waves on fluid percolation. The model shows that the low‐frequency elastic waves of relatively low intensity can significantly enhance the flow rate of a yield stress fluid under small external pressure gradients and aid in the mobilization of entrapped NAPL blobs by reducing the value of the threshold gradient needed to displace the fluid. We estimate the intensity of a sonic field to be used in the possible field implementation of this method to be in the range of 0.2–125 W/m2.

Fractals and percolation in porous media and flows?

We review a body of recent work, related to the research interests of our group, on the channel structure of disordered porous media, or fractured systems, where concepts of percolation and fractal geometry have proved useful in characterizing, or explaining, features of the transport properties of single and multiphase flow, or of the “dynamics” of invasion percolation.

Hydrodynamics of cholesteric liquid crystals in the coarse-grained limit

The hydrodynamical behaviour of cholesteric liquid crystals has been considered in the limit of low amplitude and low frequency distortions and motions. It is shown that there are interesting analogies with superfluid-hydrodynamics, such as the fountain effect, thermal superconductivity and temperature wave propagation. In certain situations, there is an unusual formation of a boundary layer at low velocities, and in certain others the properties resemble those of percolation in porous media. Results concerning some special phenomena peculiar to cholesteric liquid crystals are also presented. Finally it is pointed out that there should be two types of second sound in chiral smectic C.

Capillary displacement and percolation in porous media

We consider capillary displacement of immiscible fluids in porous media in the limit of vanishing flow rate. The motion is represented as a stepwise Monte Carlo process on a finite two-dimensional random lattice, where at each step the fluid interface moves through the lattice link where the displacing force is largest. The displacement process exhibits considerable fingering and trapping of displaced phase at all length scales, leading to high residual retention of the displaced phase. Many features of our results are well described by percolation-theory concepts. In particular, we find a residual volume fraction of displaced phase which depends strongly on the sample size, but weakly or not at all on the co-ordination number and microscopic-size distribution of the lattice elements.