Structure Of Porous Media Research Articles

Development of a computer vision-based measuring system for investigating the porous media structure

Porous materials are widely used in a variety of scientific and technological fields; therefore, a large number of publications deal with the challenges related to studying the porous media microstructure. Porosity investigation methods based on the measurement of certain physical properties of the medium are usually very complex, expensive, cumbersome, require harsh experimental conditions and are unable to determine pore size distribution. On the other hand, modern optical measuring techniques are also not universal and often need significant adaptation. In this regard, a strategy is developed that formalizes the process of direct porosity measurement of the investigated specimen using a series of its images. The proposed method performs image denoising, aggregates separation, measurement of microstructure elements and mathematical analysis of acquired data. Numerical experiments performed using CT images of a porous ceramic sample suggest the reliability of the developed technique.

3D Stochastic Network Modeling and Investigation of Network Size Effect on the Porous Media Structure of Ion Exchange Catalyst Amberlyst-35 with Computer Programs

In the present paper, the investigation was focused on the physical characterization and determination of porosity for an ion exchange catalyst called Amberlyst-35, which produces environmentally benign gasoline using 3D network modeling (3DNM). In addition, the effect of the different pore size distributions (PSD) has been investigated in porous media (PM). First, the mercury porosimetry (MPo) experiment was carried out to determine the porosity of the Amberlyst-35. Second, the KALINET program was run by Compact Visual Fortran (CVF) and Graphical Input/Output (GINO) for modeling porous structures. Then, the SECTION program was used for different porous 3D random images. The theoretical penetration curve was drawn using data obtained from the KALINET program and fitted to the experimental penetration values of Amberlyst-35 by changing the number of pores in each pressure interval of the PSD. The PSD was a 3D network model size of (N) = 30x30x30, 40x40x40, 50x50x50, which included 83,700-196,800-382,500 pores, respectively. On the other hand, various sections of the 3D stochastic images of the pore network were obtained from the SECTION program. Finally, 3D network images were drawn by the KALINET3D computer program. The MPo method has been applied using computer programs (with desktop computers). Moreover, it was found that the same results were obtained for both the theoretical and experimental data of MPo.

Effect of gas hydrate formation and dissociation on porous media structure with clay particles

Natural gas hydrates are a potential future energy modality with the advantages of clean burning and large resource reserves and have attracted worldwide attention. Natural gas hydrates formation and dissociation impact the skeletal structure and mechanical properties of porous media sediments. In addition, there is a synergistic effect between the migration of fine clay particles in porous media and hydrate behavior. In this study, methane hydrate was examined in-situ using a low-field nuclear magnetic resonance system in the presence of two suspensions of clay particles with different stability. The results showed that clay particles impacted methane hydrate formation and dissociation and the pore structure of porous media. Hydrate nucleated preferentially in large pores, causing them to split into smaller pores; the presence of clay particles, especially illite, improved the water conversion rate. The results indicated that water content in large pores increased after hydrate dissociation but was discontinuous among different pores. When illite was present, the distribution was more continuous; when montmorillonite was present, the water distribution of the large pores was similar to that of the original state. This work increases our understanding of the kinetics, water migration, and pore structure alteration of methane hydrate formation and dissociation in sediments with clay particles and provides support for the safe and efficient development of natural gas hydrates.

Mechanism of droplet motion in the typical micro-channel of porous media

The investigation of a two-phase flow in porous media has significant implications for a wide range of applications. Previous research has focused on exploring the variations in flow and phase fields in a two-phase flow using experimental and numerical methods. However, the complex structure of porous media introduces many uncertainties that can impact research outcomes. In recent years, some scholars have tried to study the dynamic mechanics of a two-phase flow through typical structures to eliminate these confounding factors. Therefore, this paper focuses on examining the flow patterns of dispersed phases with different sizes during the displacement process based on the typical micro-channel of porous media. Furthermore, the study examines various dimensionless parameters that impact alterations in the streamlines of a two-phase flow as well as the carrying capacity for dispersed phases. The findings suggest that the capillary number governs the ability of the continuous phase to transport the droplet. Consequently, the dispersed droplets tend to become trapped in weak flow regions. The dynamic mechanisms of the dispersive droplet trapping are systematically analyzed by combining the numerical simulation results and experimental evidence from previous studies. Based on these findings, the paper puts forth some mechanistic suggestions that could contribute to a more effective displacement of a two-phase flow in porous media.

Saltwater intrusion induced micro-scale mineral precipitation and evolution in porous media

Saltwater intrusion is often occurring in coastal regions, and can substantially alter the chemical properties of groundwater. Thus, the micro-processes of mineral precipitation and the subsequent pore structure of porous media will evolve. However, these micro-processes have not yet been thoroughly studied. In this work, a series of column experiments were conducted to assess the evolution of ion exchange and simulate the mixing process of saltwater-freshwater that occurred in coastal aquifers after saltwater intrusion. The spatiotemporal distribution, morphological characteristics, and elemental composition of the precipitated minerals were characterized using nano-computed tomography, scanning electron microscopy, and energy dispersive spectroscopy mapping. The results revealed that mineral precipitation occurred throughout the columns. The number of smaller-diameter minerals with larger specific surface areas increased the most. The precipitated minerals contained mainly calcium and magnesium carbonates, and the morphology of the precipitated minerals varied, including block-, needle-, cube-, and rod-like precipitates. The mineral precipitates first filled the cracks in the quartz sand and then precipitated on the surface of quartz sand. Under the effects of ion exchange and mixing, quartz sand grains in the saltwater-freshwater mixing zone tended to become oversaturated and form precipitates. Moreover, the mineral precipitates preferentially nucleated rather than increasing in volume during the precipitation.

Study of Temperature Effect on Cascade Characteristics of Nanofluidic Energy Absorption System

Nanofluidic energy absorption system (NEAS) with cascade energy absorption characteristics can absorb energy on different levels simultaneously in one system, which greatly enriches its functions and applications. The pore structure and size distribution of porous media play a crucial role in the design and construction of cascade nanofluidic systems. In this paper, two cascade pore models were constructed using carbon nanotubes with different diameters, one was the model of two tubes with both one end immersed in water (DNEAS), and the other was the model of two tubes end to end, with the end of the big tube immersed in water (SNEAS). The effects of temperature-coupled pore size on the infiltration processes of water molecules into two models were investigated. The fitting correlations between critical pore size difference and temperature were established. The microscopic mechanism of temperature effect was illuminated. With the increase in temperature, systems displaying cascade characteristics transformed into a single-stage system without cascade characteristics. Due to the significant size effect of system temperature, the critical pore difference increased with both system temperature and the pore size. The research results expanded the basic database of cascade nanofluidic systems and provided guidance for the application design of cascade nanofluidic systems.

Experimental study on thermal performance of ultra-thin heat pipe with a novel composite wick structure

The rapid advancement of high-performance electronic devices and high-capacity energy storage has prompted the development of ultra-thin heat pipes with a higher heat transfer limit, faster start-up speed, and lower thermal resistance. In the present study, a novel double-layer wick structure comprising sintered copper powder and spiral woven mesh was proposed to analyze how various combinations of porous media properties, structures, and heating surfaces influence the thermal performance of ultra-thin heat pipes. The wick structure consists of two layers: a layer of sintered copper powder with four different particle sizes and a layer of spiral woven mesh. To improve the starting characteristics, the starting time under different thermal loads was studied. Additionally, a comparison study was conducted between the ultra-thin heat pipe with a single type wick structure and the proposed wick structure. The results revealed that the ultimate power in the two horizontal states was 50 W. The thermal resistance of Horizontal-1 (heat applied to the sintered copper powder side) was 0.069 W/°C, and for Horizontal-2 (heat applied to the spiral woven mesh side), it was 0.093 W/°C, both measured at their respective ultimate thermal loads. Additionally, among all four structures in Horizontal-1, the shortest start-up time occurred at a power of 30 W, with a duration of 42 s. Finally, when compared to the single wick structure, the proposed double-layer wick structure exhibited an 11.1% increase in ultimate power.

Visual investigation on optimizing combustion characteristic of porous media burner combined with bluff body

ABSTRACT Coalbed methane as an unconventional natural gas is suitable for the utilization in thermal photovoltaic systems through optimized burners. In order to improve the radiation and utilization efficiency of coalbed methane, a combination of bluff body and porous media was proposed. Moreover, the bluff body spacing and porous media structure were changed to analyze the influence on flame characteristics. The results showed that the maximum temperature and radiation efficiency increased with decreasing of bluff body spacing. When the bluff body spacing was 30 mm, the maximum temperature of 933 K was obtained, and the radiation efficiency increased by 68%. The increase of the equivalence ratio also improved the radiation efficiency, and the maximum radiation efficiency was 14.5% at φ = 0.90. In addition, the increase of inlet velocity and bluff body spacing was beneficial to downstream flame propagation, but had a negative effect on upstream propagation. At v in = 40 cm/s, the maximum downstream propagation velocity was 0.267 mm/s. Due to the difference in thermal conductivity, flame fragmentation occurred in the 8 mm pellets, but the flame propagation was gradually stable with the increase of bluff body temperature.

Realistic geometric modeling of the dielectric constant and its effect on the discharge with a porous dielectric

Porous dielectric discharge (PDD) is a critical phenomenon in plasma catalysis, biomedical tissue surface functionalization, and all-solid-state battery design. The dielectric constant of porous dielectric (PD) significantly impacts discharge characteristics and breakdown mechanisms across different applications. However, the complex spatial structure of porous media presents challenges in diagnosing and simulating PDD, limiting our understanding of its mechanism. In this study, the real geometric model of PD obtained from x-ray computed tomography (X-Ray-μ CT) and a two-dimensional fluid model were used to simulate and analyze the effect of dielectric constant on PDD-plasma characteristics, especially the generation and disappearance of charged particles. The simulation results reveal the following: (1) At the breakdown moment, PDD is a density-unbalanced discharge where the electron density is two orders of magnitude higher than the ion density; (2) The breakdown discharge follows the most accessible channel instead of filling the entire gap, which is guided by the electron temperature gradient; and (3) It was first discovered that the breakdown voltage exhibits a saturated growth curve under the control of the dielectric constant. By combining these mechanisms, a comprehensive explanation has been provided for this phenomenon. This study offers a robust simulation and theoretical basis for understanding the breakdown characteristics of PDD.

Characterization method of core pore structure based on truncated Gaussian and its application in shale cores

The core pore structure is mainly described by fractal theory. Conventional single fractal models cannot express the multi-peak distribution characteristics of coal rock, shale, carbonate rock, and other cores. A multifractal model has numerous dimensions and discontinuous functions, making the model parameter selection difficult. Based on the capillary bundle theory and the truncated Gaussian distribution model, a model for characterizing the multi-peak distribution structure of cores is developed in this study. The model's accuracy is verified using the tested NMR experimental data of shale bimodal distribution and the cited coal trimodal distribution. This study further analyzes the influence of tortuosity and tortuosity fractal dimensions on this model. The results show that tortuosity and tortuosity fractal dimensions are conducive to improving the accuracy of the multi-peak pore structure model. The structure model, which can characterize the multi-scale and multi-peak distribution characteristics of shale pore diameter, provides a new concept for describing the pore structure of porous media.

Correction of Stokes drag for non-Newtonian flow through pack of spheres

Non-Newtonian fluids have great relevance in a wide range of porous media applications, such as enhanced oil recovery and filtration processes. The estimation of the drag coefficient of power-law fluids flowing through simple porous media structures in the Stokes regime is typically modeled by adding a direct correction term to the Newtonian model. In this study, to calculate the non-dimensional drag for various fluid indices and volume fractions of packed spheres, extensive numerical simulations of the power-law fluid flow through single cubic, body-centered cubic, and face-centered cubic porous structures are conducted. The numerical results are used to develop a model function of the non-dimensional drag depending on the power-law fluid index and volume fraction of the sphere pack. Consequently, the drag force and coefficient of shear-thinning or shear-thickening fluid flowing through the investigated structures can be predicted. A correction is introduced for the Stokes drag correlation based on the generalized Reynolds number for non-Newtonian fluids. The results of the proposed model and numerical simulations are in excellent agreement with deviations not more than 1.2%. This implies that the modeled predictions are valid for all investigated structures.

Volumetric measurement of a Newtonian fluid flow through three-dimensional porous media using Lagrangian particle tracking (Shake-the-Box) technique

This work experimentally investigates the pressure-driven flow of a pure Newtonian fluid through three-dimensional (3D) porous media models. The porous media model consists of square arrays of rods that also could be interpreted as a periodic tandem rod arrangement. We employed a time-resolved three-dimensional particle tracking velocimetry (3D Shake-the-Box) technique for a range of Reynolds numbers 111 ≤ R e ≤ 890 to observe flow structures and vortex formation between the rods in porous media structures with different porosities of ε = 0.7 , 0.8 , and 0.9 , which corresponds to the spacing ratio of L D = 1.75 , 2 , and 3, where L is the distance between the centers of the rods, and D is the diameter of the rods. For all the examined cases, we further analyzed the effect of the Reynolds number and the spacing ratio on the instantaneous and averaged patterns of velocity, vorticity, and the other flow parameters after obtaining the two-dimensional velocity fields using the bin-averaging method. We observed both symmetrical and asymmetrical patterns of structure and recirculation regions between the rods depending on the Reynolds number and spacing ratio. Increasing the Reynolds number reduced the symmetrical patterns of flow structures with respect to the centerline of the gap region, while the spacing ratio was randomly affecting the symmetry degree. Vortex shedding was considerable for the two examined high Reynolds numbers of Re = 444 and Re = 890 behind the upstream rod as the porosity increased. The backward movement of the reattachment point has been observed by increasing the Reynolds number.

CFD Investigation of an Innovative Additive Manufactured POCS Substrate as Electrical Heated Solution for After-Treatment Systems

In the last decade, additive manufacturing (AM) techniques have been progressively applied to the manufacturing of many mechanical components. Compared to traditional techniques, this technology is characterized by disruptive potential in terms of the complexity of the objects that can be produced. This opens new frontiers in terms of design flexibility, making it possible to create new components with optimized performances in terms of mechanical properties and weight. In this work, the focus is on a specific field of application: the development of novel porous media structures which can be the basis of advanced after-treatment systems for internal combustion engines. In particular, the possibility to design periodic open cellular structures (POCSs) that can be applied as catalytic substrates opens new perspectives in terms of flexibility and integrated functionalities. The present study investigates an innovative solution where the catalytic substrates are located in the pipes of the exhaust manifolds of a high-performance engine. A preliminary characterization of the pressure drop induced by the POCS structure is carried out, with a particular focus on the impact of the backpressure on the engine performances. Moreover, each POCS integrates an electrical circuit which is used to promote the heating of the device, with beneficial effects on the light-off of the catalytic reactions. An advanced CFD model is applied to evaluate the potential of the solution, comparing the pollutant conversion with that of the baseline configuration equipped with a standard after-treatment system solution.

A Pore-Scale Physical Model for Electric Dewatering of Municipal Sludge Based on Fractal Geometry

Water in municipal sludge has an electric double layer (EDL), and can be rapidly removed via electroosmosis. However, the understanding of the physical mechanisms of electroosmosis is limited owing to the complex pore structure of sludge porous media, which may restrict the development of electric dewatering (EDW) technology. In this study, the sludge microstructure was measured using the computerized tomography technique and quantitatively characterized using fractal geometry. A new pore-scale physical model for the electroosmotic flow through sludge porous media was developed based on the EDL theory, and the analytical expressions for the electroosmotic flow rate and permeability coefficient were determined. The proposed fractal pore-scale model for electroosmotic flow was validated by comparing it with the measured electroosmotic flow rate using a self-designed EDW device for municipal sludge composed of a hydraulic system and applied electric field. The results show that the electroosmotic flow rate of sludge porous media depends not only on the applied electric field, but also on the sludge microstructure including porosity, maximum pore size, and pore and tortuosity fractal dimensions. However, the correlation between the electroosmotic flow rate and the voltage gradient was usually nonlinear, and became linear only if the tortuosity fractal dimension equaled to one (straight flow path). The electroosmotic permeability coefficient increases with an increase in porosity; however, it is lowered by the increased pore and tortuosity fractal dimensions under a certain porosity. The electroosmosis phenomenon can effectively remove part of the interstitial water and surface water in sludge porous media, and the proposed electroosmotic physical model provides a useful theoretical basis for the development of EDW technology for municipal sludge.

An Intelligent Denoising Method for Nuclear Magnetic Resonance Logging Measurement Based on Residual Network

Nuclear magnetic resonance (NMR) is an important geophysical technique for the structure and properties measurement of porous media. The small-diameter NMR logging technology has been emerged as a useful tool in terms of evaluating the shallow surface hydrogeological parameters. However, the NMR logging is always suffering from the low signal-to-noise radio (SNR). This paper proposes a denoising network for NMR logging signal based on the combination of the convolutional neural network (CNN) and residual learning, called as Dn-ResNet. Firstly, a large amount training datasets are constructed according to the characteristics of the NMR logging signal and noise, which is used to train the network. Secondly, the useful features of the NMR logging signals are learned by the network during training processing, in which the residual learning mechanism is employed to improve the training efficiency and the denoising performance. As a result, the Dn-ResNet may realize adaptive denoising without manual filter parameters tuning, prior knowledge of NMR logging signals and preprocessing of the original noisy signals. The performance of the proposed denoising network is demonstrated on both the synthetic NMR logging signals and field data. The effective signals are obtained from the noisy signals at different SNRs. In addition, an attempt to use the well-trained Dn-ResNet to deal with a single record provides similar results compared to 200 stacks. It shows that the number of stacks may be reduced to shorten the measurement time and improve the measurement efficiency. The results show the effectiveness and robustness of the proposed approach, which enables the technology of deep learning to be developed in application of NMR logging data processing.

Mobility of antipyretic drugs with different molecular structures in saturated soil porous media.

In the post-COVID-19 era, extensive quantities of antipyretic drugs are being haphazardly released from households into the environment, which may pose potential risks to ecological systems and human health. Identification of the mobility behaviors of these compounds in the subsurface environment is crucial to understand the environmental fate of these common contaminants. The mobility properties of three broad-spectrum antipyretic drugs, including ibuprofen (IBF), indometacin (IMC), and acetaminophen (APAP), in porous soil media, were investigated in this study. The results showed that the mobility of the three drugs (the background electrolyte was Na+) through the soil column followed the order of APAP > IBF > IMC. The difference in the physicochemical characteristics of various antipyretic drugs (e.g., the molecular structure and hydrophobicity) could explain this trend. Unlike Na+, Ca2+ ions tended to serve as bridging agents by linking the soil grains and antipyretic molecules, leading to the relatively weak mobility behaviors of antipyretic drugs. Furthermore, for a given antipyretic drug, the antipyretic mobility was promoted when the background solution pH values were raised from 5.0 to 9.0. The phenomenon stemmed from the improved electrostatic repulsion between the dissociated species of antipyretic molecules and soil grains, as well as the weakened hydrophobic interactions between antipyretic drugs and soil organic matter. Furthermore, a two-site non-equilibrium transport model was used to estimate the mobility of antipyretic drugs. The results obtained from this work provide vital information illustrating the transport and retention of various antipyretic drugs in aquifers.

PREDICTING THE ELECTRICAL CONDUCTIVITY OF DUAL-POROSITY MEDIA WITH FRACTAL THEORY

The microspatial structure of porous media affects the electrical properties of reservoir rocks significantly. In this work, a dual-porosity model is established to investigate the electrical properties of porous media, in which tree-like networks and capillary channels represent fractures and pores. By using fractal theory, we established an analytical equation for the conductivity of water-saturated dual-porosity media. The analytical equation, devoid of any empirical constants, expresses the electrical properties of the porous media as a function of some structural parameters ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text]. We also examine the impact of various matrix structural parameters on conductivity. It is found that increasing the length of mother channel ([Formula: see text], length ratio ([Formula: see text], the number of branching layers ([Formula: see text], and tortuosity fractal dimension ([Formula: see text] leads to a decrease in conductivity, whereas increasing the diameter of mother channel ([Formula: see text], diameter ratio ([Formula: see text], the cross-sectional porosity ([Formula: see text], [Formula: see text], and the channel bifurcation number ([Formula: see text] enhances conductivity. Furthermore, we validated this analytical model by comparing it with the experimental data available, and the results demonstrate good agreement. This research has proposed an advanced conductivity model that enables us to better understand the underlying physical mechanisms of the electrical properties in porous media.

Evolution of pore structure and radon exhalation characterization of porous media grouting

Cracks and pores are considered as major sources of radon. Cement is widely used as a grouting material in mines, tunnels, and other projects for reinforcement, seepage prevention, and water plugging. This paper mainly experimentally studied the correlation between the radon exhalation rate of the porous medium after grouting and the sand grain diameter, grouting pressure, and slurry water-cement ratio. The pore characteristics of the samples before and after grouting were also studied based on the low field nuclear magnetic resonance (LF-NMR). The findings of the study show that the porosity of samples increases after the superfine cement solidification with an increase in the water-cement ratio, and the radon exhalation rate is proportional to porosity, the radon exhalation rate increases by 0.0005 Bq·m–2/s at W/C = 1.5, and by 0.0017 Bq·m−2/s at W/C = 2 increases, in comparison to the W/C = 1.The radon exhalation rate of porous media gradually increased after grouting in response to an increase in grouting pressure and the water-cement ratio. The radon exhalation rate of the porous media with larger pores was relatively higher and exhibited a positive correlation with the volume of micropores in porous media，the correlations of coarse, medium and fine media are 0.815, 0.826, and 0.859. The change in pore structure has an influence on radon exhalation. Although grouting changes the pore structure and reduces the connectivity between internal pores, the micropores generated after cement slurry solidification improves the radon exhalation rate by providing new channels, When the water-cement ratio is 1.5 and the grouting pressure is 1.5 MPa, the radon exhalation rate of porous media is 0.00273 Bq·m−2/s. The research results serve as a reference basis for the evaluation of the impact of rock masses on grouting reinforcement and pore sealing.

Modified UNet with attention gate and dense skip connection for flow field information prediction with porous media

Porous media flow phenomena are commonly found in nature and industry. Understanding the patterns can improve industrial production and efficiency. Traditional numerical methods can predict flow field information within porous media exactly, even on pore scale. However, once the pore structures of porous media are changed, the traditional numerical methods have to start over again, which implies poor extension and low efficiency for realistic application. To address the challenge, we propose a new deep learning method for image segmentation based on convolutional neural networks that can quickly predict the saturation variation and flow velocity profile of multiphase flow directly from the structure of porous media. In the present method, the UNet network structure is improved by replacing parallel splicing with different levels of dense skip connection to extract flow information at different depths. When processing flow topological information, the introduction of attention mechanism allows effective focus on adjusting the flow field edges and front shapes to improve accuracy. Depending on the pore structures information, the saturation of the porous media also can be evaluated. This result shows that the flow field information (saturation and velocity) of porous media can be quickly predicted by deep learning methods. Compared with the computational fluid dynamics (CFD) method, this approach has a better prediction efficiency for porous media. The machine learning method is a good prediction tool for porous media with different porosities and pore structures.

Pore-scale investigation on mineral dissolution and evolution in hydrological properties of complex porous media with binary minerals

A pore-scale numerical model for reactive transport process based on lattice Boltzmann method is adopted to simulate the mineral dissolution in complex porous media with binary minerals. The effect of binary mineral, solute concentration and dissolution rate on hydrological properties evolution of complex porous media is investigated. Simulation results show that binary minerals could inhibit the mineral dissolution and further alter the temporal evolution trend of related hydrological properties compared to monomineralic porous media. Changes in pore structure of complex porous media could be divided into three stages: slow increase, significant increase and slightly-stable increase stage in succession. A simple model is barely suitable for characterizing the porosity-permeability evolution of the complex porous media. Temporal evolution in reactive specific surface during mineral dissolution could be characterized by the fractal model. Although solute concentration could change the mineral dissolution process, it has no effect on the evolution relationship of hydrological properties between permeability, reactive specific surface and porosity. Mineral dissolution rate would alter the above-mentioned relationships by changing the reactive transport regime.