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This study explores hydrogen production via steam methane reforming (SMR) within complex Voronoi catalytic foams. Pioneering pore-scale analysis unveils the intricate interplay between foam geometry and SMR performance, surpassing conventional macro-scale studies. The highly intricate Voronoi foams intrigue due to their maximized surface area and efficient heat transfer. The research meticulously examines the combined effects of various factors like inlet velocity, temperature, foam properties, and steam-to-carbon ratio on hydrogen yield. Employing OpenFOAM's finite volume method, pore-scale simulations were conducted. Each investigated parameter significantly impacted hydrogen production, with temperature boasting the most remarkable influence. A 142.5% surge in hydrogen production was observed when increasing the temperature from 1100 to 1200 K. Lengthening the foam from 5 mm to 10 mm yielded a 90% increase. This groundbreaking study highlights the immense potential of Voronoi foams to revolutionize SMR processes, paving the way for cleaner and more sustainable energy solutions. [Display omitted] • The SMR process is simulated in a catalytic environment with pore-scale perspective. • Effect of velocity, temperature, S/C ratio & porosity on H 2 generation is analyzed. • Temperature has a greater impact on hydrogen mass flow rates. • Voronoi catalytic foam structure can highly affect heat transfer & hydrogen production. • 90% increase in hydrogen production rate observed by doubling the length of the foam. [ABSTRACT FROM AUTHOR]

This study utilises computational fluid dynamics simulations with the OpenFOAM computational framework to investigate and compare the in-plane and through-plane permeability properties of four different gas diffusion layers (GDLs). Also the through-plane water and air relative permeability values and water saturations at different rates were simulated. Permeability analysis enhances our understanding of fluid flow, ways to decrease pressure loss in the GDL, and methods to enhance oxygen concentration at the catalyst layer interface through convection. The analysis reveals that the investigated GDL materials have spatial heterogeneity of porosity and permeability, especially in the Sigracet SGL 25 BA GDL. However, the porosity and permeability of the Toray TGP-H 060 and AvCarb 370 MGL GDLs exhibit less variations. The two-phase flow studies on GDL saturation show that at the same water injection flowrate, the AvCarb 370 MGL GDL has the largest remaining water saturation, with Sigracet SGL 25 BA GDL being the less saturated GDL among the four investigated GDLs. The compression from the ribs significantly affected the in-plane permeabilities of both Toray TGP-H 060 and especially impacted Sigracet SGL 25 BA GDL. This impact was expected as the pore size distribution varied significantly in the areas under the ribs versus the channel. [ABSTRACT FROM AUTHOR]

The porous structures of the catalyst layer (CL) for proton exchange membrane (PEM) fuel cells were reconstructed using the sphere-based simulated annealing (SA) method, in which different carbon sphere diameters, carbon phase fractions, ionomer loadings, and porosities were achieved to simulate different samples. The pore-scale simulation model based on the random walk algorithm was developed to evaluate the tortuosity in the CL. The results show that the carbon phase fraction, particularly the carbon sphere diameter, significantly influences the tortuosities in both pores and ionomer. Larger carbon spheres contribute to tightening the solid phase and enlarging the pore size within the CL, thereby affecting the pore structure and the ionomer distribution. The tortuosity obtained from the random walk algorithm aligns well with those from pore-scale diffusion and flow simulations using the Lattice–Boltzmann method (LBM). The random walk algorithm has the highest efficiency of the three methods in calculating the tortuosity of the CL when the porosity is less than 0.2, demonstrating its wider applicability. This study further proposes formulas for predicting the tortuosities in both pores and ionomer, which are closer to actual CLs than empirical equations. In addition, the present work confirms that the structural randomness resulting from the reconstruction method used in this work has little effect on the tortuosity, indicating that a small number of reconstructed samples suffice for investigating transport processes in the CL. Overall, our research contributes to the prediction of the properties of real porous media in energy engineering. Practical Applications: This manuscript reports on the reconstruction of the catalyst layer in proton exchange membrane fuel cells using the simulated annealing method under some appropriate assumptions. A pore-scale simulation using a random walk algorithm was performed to compute the tortuosity both in the pores and in the ionomer, which is compared with pore-scale diffusion and flow simulations using the Lattice–Boltzmann method. A parametric study for several geometric parameters was carried out. Some conclusions are drawn from the results of the pore-scale simulations, and several formulas are proposed accordingly. This study helps to predict the tortuosity in the porous structure closer to the actual porous medium than the empirical equations. Meanwhile, the proposed tortuosity formulas improve the accuracy of the macroscopic models compared to using the assumed transmission parameter values. In addition, structural randomness analysis is explored, which will further reduce the workload in actual engineering calculations and improve computational efficiency. [ABSTRACT FROM AUTHOR]

Abstract This study utilises computational fluid dynamics simulations with the OpenFOAM computational framework to investigate and compare the in-plane and through-plane permeability properties of four different gas diffusion layers (GDLs). Also the through-plane water and air relative permeability values and water saturations at different rates were simulated. Permeability analysis enhances our understanding of fluid flow, ways to decrease pressure loss in the GDL, and methods to enhance oxygen concentration at the catalyst layer interface through convection. The analysis reveals that the investigated GDL materials have spatial heterogeneity of porosity and permeability, especially in the Sigracet SGL 25 BA GDL. However, the porosity and permeability of the Toray TGP-H 060 and AvCarb 370 MGL GDLs exhibit less variations. The two-phase flow studies on GDL saturation show that at the same water injection flowrate, the AvCarb 370 MGL GDL has the largest remaining water saturation, with Sigracet SGL 25 BA GDL being the less saturated GDL among the four investigated GDLs. The compression from the ribs significantly affected the in-plane permeabilities of both Toray TGP-H 060 and especially impacted Sigracet SGL 25 BA GDL. This impact was expected as the pore size distribution varied significantly in the areas under the ribs versus the channel.

In this work, a series of porous medium with Gyroid Triply Periodic Minimal Surfaces (G-TPMS) structures were established for lean concentration methane combustion. Based on pore-scale numerical simulations, the influence of TPMS parameters on porous media combustions, as well as the shape of flame surface in different TPMS structures, heat transfer characteristics between solids and fluids, the radiation characteristics and heat flux on the solid surface were investigated. Results show that, under the same inlet flow rate and equivalence ratio, the value and axial location of the maximum average fluid temperature will be changed due to the difference in porosity and flow resistance of each structure. For the G-TPMS structures' porous medium, the change of structure period had a greater impact on the combustion compared with the wall thickness. And, in the G-TPMS structures' porous medium, the flame surface always shows a finger structure. The flow rate that shows the same increase trend with the fluid temperature in the preheating region, which has a periodic change like the porosity in the axial direction. Based on the results, it can be seen that the region of solid-to-solid surface radiative heat transfer and fluid-solid heat flux on the interface was also changed due to the influence of flame front position. [ABSTRACT FROM AUTHOR]

The catastrophic effects of climate change can be mitigated by transitioning to renewable energy sources such as wind, solar, and hydropower while utilizing hydrogen (H 2) as an energy carrier. As renewable fuel sources are intermittent and location-specific, large-scale, long-term storage options for H 2 must be explored with high necessity. Subsurface hydrogen storage in saline aquifers provides a vital scope to store H 2 gas in available pore voids with minimal environmental risk. In this work, a highly heterogeneous porous micromodel was used to study the immiscible two-phase dynamics at high-temperature, high-pressure saline aquifer conditions using computational fluid dynamics (CFD) simulation based on volume of fluid (VOF) method. A set of microfluidic experiments were carried out under atmospheric conditions to validate the numerical model. The VOF model was observed to show good agreement with microfluidic experiments. An unstable displacement pattern with viscous fingering was observed during various flow conditions that captured high pressure (15 and 25 MPa) and temperature conditions (323 and 343 K). It was observed that fingering displacement of brine limits the storage spaces for hydrogen, which consequently follows the high permeable path. As a result, only 0.272 fraction of brine was invaded by the H 2 at a temperature of 323 K and pressure of 15 MPa. A comparison between H 2 -brine and nitrogen (N 2)-brine flow dynamics revealed a 46% less storage capacity of porous media for H 2. Formations bearing high temperature (343 K) showed an 11.27% increase in H 2 storage capacity, while pressure increase had negligible effect. At low capillary number (Ca), more snap-off effects resulted in higher trapping of H 2 gas. This study aims to provide meaningful insights into the complexities of flow dynamics and displacement patterns that are crucial for optimizing hydrogen storage efficiency in saline aquifers and for potential 'white' hydrogen production. [Display omitted] • Hydrogen-brine two-phase flow was simulated in a heterogeneous porous media. • Simulation captures pressure and temperature conditions of geological aquifers. • Microfluidic experiments were carried out to validate the numerical model. • Viscous fingering under high-pressure and temperature limits hydrogen storage. • More snap-off effects lead to increased hydrogen trapping in porous media. [ABSTRACT FROM AUTHOR]

Complex physical phenomena take place while dealing with the convective heat transfer in porous medium. Due to involved complexities, most of the earlier numerical studies are performed using various porous models compromising the detailed phenomena. Therefore, a pore-scale simulation has been performed for convective heat transfer in triply-periodic-minimal-surface lattices, with identical void fraction and unit-cell size, but different geometrical shapes (tortuosity), namely Diamond, Inverted Weaire–Phelan, Primitive, and Gyroid. Further, each lattice derived into three different types of porous structures by designing second subdomain as solid (in Type 1), fluid (in Type 2), and microporous zones (in Type 3). The convective heat transfer in a square mini-channel filled with the porous structures is investigated for the range of flow Reynolds number 0.01 < Re < 100 and Pr = 7 . The temperature distributions, solid and fluid Nusselt numbers on the external walls and on the internal walls, and quantitative departure from local thermal equilibrium (LTE) assumption are calculated for different porous media. The effect of porous morphology/tortuosity and effective porosity on the heat transfer is examined. The results revealed that the maximum temperature within the domain is found in Type 2 treatment, leading to inferior heat transfer performance compared to Type 1 and Type 3. Among all the lattices, the Diamond lattice provides more uniform temperature distribution over the external walls and within the volume including solid and fluid. The effective and the internal Nusselt numbers increase drastically for Re > 10. For the range of Re considered here, the Primitive lattice shows the maximum deviation from LTE assumption. [ABSTRACT FROM AUTHOR]

The development of methane hydrate extraction technology remains constrained due to the limited physical understanding of hydrate dissociation dynamics. While recent breakthroughs in pore-scale visualization techniques offer intuitive insights into the dissociation process, obtaining a profound grasp of the underlying mechanisms necessitates more than mere experimental observations. In this research, we introduce a two-phase micro-continuum model that facilitates the numerical simulation of methane hydrate dissociation at both single- and multiscale levels. We employed this numerical model to simulate microfluidic experiments and determined the kinetic parameters of methane hydrate dissociation based on experimental data under various dissociation scenarios. The simulations, once calibrated, correspond closely to experimental results. By comprehensively comparing the simulated results with experimental data, the rate constant and the effective diffusion coefficient were reliably determined to be kd = 1.5 × 108 kmol2/(J·s·m2) and Dl = 0.8 × 10−7 m2/s, respectively. Notably, the multiscale model not only matches the precision of the single-scale model but also presents considerable promise for streamlining the simulation of hydrate dissociation across multiscale porous media. Moreover, we contrast hydrate dissociation under isothermal versus adiabatic conditions, wherein the dissociation rate is significantly reduced under adiabatic conditions due to the shifted thermodynamic condition. This comparison highlights the disparities between microfluidic experiments and real-world extraction environments. [ABSTRACT FROM AUTHOR]

CO2 capture and storage technology is favorable for the reduction of CO2 emissions. In recent years, a great number of research achievements have been obtained on CO2 geological storage from nano scale to oil/gas reservoir scale, but most studies only focus on the flow behaviors in single-dimension porous media. Besides, the physical experiment method is influenced by many uncertain factors and consumes a lot of time and cost. In order to deeply understand the flow behaviors in the process of CO2 geological storage in microscopic view and increase the volume of CO2 geological storage, this paper established 2D and 3D models by using VOF (Volume of Fluid) method which can track the dynamic change of two-phase interface, to numerically simulate supercritical CO2-brine two-phase flow. Then, the distribution characteristics of CO2 clusters and the variation laws of CO2 saturation under different wettability, capillary number and viscosity ratio conditions were compared, and the intrinsic mechanisms of CO2 storage at pore scale were revealed. And the following research results were obtained. First, with the increase of rock wettability to CO2, the sweep range of CO2 enlarged, and the disconnection frequency of CO2 clusters deceased, and thus the volume of CO2 storage increased. Second, with the increase of capillary number, the displacement mode transformed from capillary fingering to stable displacement, and thus the volume of CO2 storage increased. Third, as the viscosity of injected supercritical CO2 gradually approached that of brine, the flow resistance between two-phase fluids decreased, promoting the ''lubricating effect''. As a result, the flow capacity of CO2 phase was improved, and thus the volume of CO2 storage was increased. Fourth, the influence degrees of wettability, capillary number and viscosity ratio on CO2 saturation were different in multi-dimensional porous media models. In conclusion, the CO2-brine two-phase flow simulation based on VOF method revealed the flow mechanisms in the process of CO2 geological storage at pore scale, which is of guiding significance to the development of CCUS technology and provides theoretical guidance and technical support for the study of CO2 geological storage in a larger scale.

Multiphase flow in porous media often occurs with the formation and coalescence of fluid ganglia. Accurate predictions of such mechanisms in complex pore geometries require simulation models with local mass conservation and with the option to improve resolution in areas of interest. In this work, we incorporate patch-based, structured adaptive mesh refinement capabilities into a method for local volume conservation that describes the behaviour of disconnected fluid ganglia during level set simulations of capillary-controlled displacement in porous media. We validate the model against analytical solutions for three-phase fluid configurations in idealized pores containing gas, oil, and water, by modelling the intermediate-wet oil layers as separate domains with their volumes preserved. Both the pressures and volumes of disconnected ganglia converge to analytical values with increased refinement levels of the adaptive mesh. Favourable results from strong and weak scaling tests emphasize that the number of patches per processor and the total number of patches are important parameters for efficient parallel simulations with adaptive mesh refinement. Simulations of two-phase imbibition and three-phase gas invasion on segmented 3D images of water-wet sandstone show that adaptive mesh refinement has the highest impact on three-phase displacements, especially concerning the behaviour of the conserved, intermediate-wet phase. [ABSTRACT FROM AUTHOR]

Nanofluids have broad prospects in enhancing the oil recovery of reservoirs with low porosity, low permeability, high capillary pressure and low oil recovery. However, the modification effects of nanofluids on tight glutenite reservoirs remain unknown. In this paper, nanofluids with different proportions of silica nanoparticles and sodium dodecyl sulfate were prepared and characterized by zeta potential and particle size distribution. Then, the effects of nanofluids on interfacial tension and reservoir wettability were examined. Next, a computational fluid dynamics method was adopted to further investigate the effects of nanofluids and injection pressure on enhancing oil recovery of the Baikouquan Formation at the pore scale. The experimental results showed that all prepared nanofluids are stable systems with uniform dispersion. The interfacial tension between the nanofluids and oil was reduced by up to 8.01% compared with water, and the reservoir wettability was changed from intermediate-wet to strong hydrophilicity. The simulation results revealed that the water and nanofluid flooding processes could be divided into two stages: the initial channel establishment stage and the channel expansion stage. In the initial stage, the nanofluids hardly showed an enhanced oil recovery effect due to the faster and sharper migration fronts. In the channel expansion stage, the nanofluids clearly showed an enhanced oil recovery effect, as the nanofluids could displace the oil in the relative dead pores during water flooding. After 10 pore volume injection of displacement fluid at an injection pressure of 1 MPa, the oil recovery using NF5 was highest at 76.58%. In addition, a higher injection pressure led to the extraction of relative dead oil at a lower injection pressure near the inlet with a smaller sweep area near the outlet; the effect on recovery has both advantages and disadvantages. [ABSTRACT FROM AUTHOR]

Biomass char morphology affects combustion behavior at the particle scale for zone II conditions, in which both heterogeneous reaction and intra-particle diffusion govern the overall rate. Furthermore, particle-scale processes affect reactor-scale outputs, and reactor-scale simulations are sensitive to particle-scale models. However, most char particle combustion models employ coarse-grained, effective-continuum approaches, which treat all porosity at the subgrid-scale. Effective-continuum approaches are not valid or accurate in the presence of large, irregular pores which can approach the size of the particle. A 3-D, pore-resolving CFD simulation approach using real biomass char particle geometries obtained from X-ray micro-computed tomography (micro-CT) is therefore used to examine the impact of morphology on zone II combustion for pulverized (∼100 µm) biomass char particles for the first time. In contrast to larger, millimeter to centimeter sized particles, the sub-millimeter, high aspect ratio biomass char particles exhibited localized reactant penetration into the innermost regions of the particles, facilitated by the presence of large pores connected to the external surface. The oxygen mole fraction distributions were governed by the large pore morphology, were non-monotonic with distance from the surface, and achieved minima in thick microporous char regions surrounding the large pores. A comparison between the pore-resolving simulation and an equivalent, spatially resolved, effective-continuum simulation revealed that even in the microporous char, the effective-continuum model underpredicted reactant penetration. A careful comparison was then performed between 30 pore-resolving particle simulations and several effectiveness factor models that employed particle-specific parameters. Commonly used uniform cylinder models significantly underpredicted effectiveness factors for these real pulverized pine char particles, while accessible hollow cylinder models achieved less than 10% relative error when averaged over all 30 particles. [ABSTRACT FROM AUTHOR]

A popular equation that is often employed to represent the relationship between the pressure loss and the fluid flow in fluidized or packed granular beds is the Ergun equation, which is an extension of Darcy's law. In this paper, the method of Smoothed Particle Hydrodynamics (SPH) is used to numerically study the flow field across a rectangular channel partially filled with a porous layer both at the Representative Elementary Volume (REV) scale using the Ergun equation and at the pore scale. Since the flow field can be estimated at the REV scale with a much lower cost compared to the pore scale, it is important to evaluate how accurately the pore-scale results can be reproduced at the REV scale. The comparison between both scales is made in terms of the velocity profiles at the outlet of the rectangular channel and the pressure losses across the clear and porous zones for three different arrays of solid grains at the pore scale. The results show that minimum differences in the flow structure and velocity profiles between the REV and the pore scale always occur at intermediate values of the porosity ( ϕ = 0.44 and 0.55). As the porosity increases, the differences between the REV and the pore scale also increase. The details of the pressure losses are affected by the geometry of the porous medium. In particular, we find that the pressure profiles at the REV scale match those at the pore scale almost independently of the porosity only when the grains are uniformly distributed in a non-staggered square array. [ABSTRACT FROM AUTHOR]

The flow of non-Newtonian fluids through evolving porous media is involved in important processes including blood flow and remediation of deformable aquifers. However, the effects of a moving solid boundary and the coupling between fluid rheology and solid deformation are still unclear. This study considers the steady and oscillatory flows of a yield stress fluid through a bundle of deformable channels. Simple semi-empirical expressions to predict the relationships between Darcy velocity and pressure gradient as a function of pore sizes, shear-rheology parameters and inlet pressure are developped, based on the results of innovative numerical simulations. The results show that channel deformation reduces the minimum pressure gradient required to induce the flow of a yield stress fluid through a porous medium, which results in lower values of Darcy-scale viscosity. For the considered conditions, macroscopic flow can be accurately predicted without a detailed knowledge of the hydraulic conductances of the deformed pores. • Numerical simulation of the flow of yield stress fluids in deformable porous media. • A semi-empirical model to predict these flows at the Darcy scale is proposed. • Viscosity heterogeneity alters pressure and velocity maps in deformable ducts. • Pressure threshold for yield stress fluid flow is lower in deformable channels. • Darcy-bulk viscosity shift factor increases for high injection velocities. [ABSTRACT FROM AUTHOR]

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Advanced high-temperature oxidation resistance is a crucial characteristic of metallic materials in porous burners. Extreme combustion conditions could lead to oxidation-affected erosion of porous media at a long-time period of burner operation. In this paper, we numerically simulated oxide scale growth at a porous radiant burner fabricated by Ni-Al intermetallic alloy using the combustion synthesis method, focusing on the structure degradation caused by periodic oxide scale spallation. A three-dimensional geometrical model of a porous intermetallic scaffold was obtained by scanning the porous burner using the X-ray CT technique. The surface erosion was modeled by the surface reconstruction based on calculated values of spalled oxide layer thickness. The simulation revealed that the submerged flame results in non-uniform distribution of the temperature at the solid surface. Such non-isothermal conditions lead to a two-times thicker oxide scale at the external surface of the burner. Thin struts of the intermetallic scaffold are prone to oxidation-affected erosion first, which forms discontinues and further fragmentation. The porous scaffold could lose about 50% of initial weight before fragmentation under conditions with intense oxide spallation. In such large structural degradation, the average flow velocity could reduce by a factor of 3, leading to changing of flame stabilization region. [ABSTRACT FROM AUTHOR]

The modeling of flow and heat transfer in porous media systems has always been a challenge, and the extended Darcy transport models are used for macro-level analysis. However, these models are subjected to the limitations depending upon the porous geometry such as pore size, pore type, effective porosity, tortuosity, permeability, and the flow characteristics. The forced convective flow of an incompressible viscous fluid through a channel filled with four different types of porous geometries constructed using the Triply Periodic Minimal Surface (or TPMS) model is presented in this study. Four TPMS lattice shapes, namely Diamond, I-WP, Primitive, and Gyroid, are created with same volume fraction of solid subdomain as 0.68 (or void fraction as 0.32). Using different configurations for the solid subdomain by treating it as (a) solid, (b) fluid, and (c) porous zone, three different classes of porous structures are further generated for each TPMS lattice. The present study is executed with the objective to investigate the effect of shape–morphology, tortuosity, microporosity, and effective porosity on permeability and inertial drag factor. A pore-scale direct numerical simulation approach is performed for the first two types of porous media by solving the Navier–Stokes equations. The specific microporosity is quantitatively induced in the solid subdomain where Darcy–Forchheimer equation is solved, whereas the Navier–Stokes equations are solved for the void subdomain in the third type of porous media. The results reveal that Darcy flow regime exists up to the mean velocity value of U < 0.0025 m/s (Re < 10) for all the cases discussed here, and it deviates at the higher mean velocity. The conductance to the flow shown by Darcy number has the maximum and minimum values for the Primitive Type 2 and I-WP Type 1 cases. The inertial drag coefficient is minimum in Diamond lattice and maximum in Primitive lattice at lower porosity (0.32), while Primitive lattice has minimum and I-WP lattice has maximum value of inertial drag coefficient for higher porosity (~ 1). [ABSTRACT FROM AUTHOR]

The development of methane hydrate extraction technology remains constrained due to the limited physical understanding of hydrate dissociation dynamics. While recent breakthroughs in pore-scale visualization techniques offer intuitive insights into the dissociation process, obtaining a profound grasp of the underlying mechanisms necessitates more than mere experimental observations. In this research, we introduce a two-phase micro-continuum model that facilitates the numerical simulation of methane hydrate dissociation at both single- and multiscale levels. We employed this numerical model to simulate microfluidic experiments and determined the kinetic parameters of methane hydrate dissociation based on experimental data under various dissociation scenarios. The simulations, once calibrated, correspond closely to experimental results. By comprehensively comparing the simulated results with experimental data, the rate constant and the effective diffusion coefficient were reliably determined to be kd = 1.5 × 108 kmol2/(J·s·m2) and Dl = 0.8 × 10−7 m2/s, respectively. Notably, the multiscale model not only matches the precision of the single-scale model but also presents considerable promise for streamlining the simulation of hydrate dissociation across multiscale porous media. Moreover, we contrast hydrate dissociation under isothermal versus adiabatic conditions, wherein the dissociation rate is significantly reduced under adiabatic conditions due to the shifted thermodynamic condition. This comparison highlights the disparities between microfluidic experiments and real-world extraction environments.

Water injection with an oscillatory pressure boundary is a promising technology, which can achieve a more economical and environment-friendly EOR (enhanced oil recovery). However, due to the unclear critical injection frequency, its oil production performance has been unstable and is far from reaching the optimal level. Here, a numerical model is established for oil recovery by the water injection with the oscillatory boundary condition to find out the critical frequency for the optimal EOR. The correlations between the water injection frequency and the EOR level at diverse oil–water surface tensions and oil viscosities are integrated into the model. Our numerical model reveals that an optimal EOR of roughly 10% is achieved at the critical water injection frequency compared with water injection without an oscillatory boundary. The EOR mechanism is revealed showing that upon water injection with the optimum frequency, the formation of the preferential pathways is inhibited and the pressure transmits to the wall sides to displace the oil. Moreover, it is indicated that the required critical frequency increases with higher surface tension and larger oil viscosity. In addition, the difference between the residual oil saturation at the optimal frequency increases with the increase in surface tension compared with water injection without an oscillatory boundary. Last but not least, it is elucidated that at a constant injection frequency, a higher EOR is achieved when the water–oil surface tension is lower but the oil viscosity is larger. Our work promises economic, eco-friendly and controllable enhanced oil recovery. [ABSTRACT FROM AUTHOR]

Traditional approaches for transport in porous media rely on empirical hydrodynamic/transport parameters to quantify the interfacial exchange terms between fluid and solid, which leads to considerable uncertainties and also to a narrow application range of each method for realistic investigations of porous media. A parameter-free approach for flow, transport, and chemical reactions in porous media is presented in this paper. This approach adopts a novel, single-domain set of equations that are rigorously derived based on the elementary conservation laws describing the physical, continuous domain. The impact of the solid on nearby fluid being directly quantified in terms of the quantity to be solved, this avoids the introduction of empirical parameters. Various transport problems including external, conjugate, and reactive processes are properly formulated in this context, with the coupling between fluid and porous structures at different scales naturally solved in a monolithic manner. All these equations remain simple in terms of their numerical implementation, with solid structures represented by the porosity field on a background mesh. The application of the present method in both pore-scale and representative elementary volume (REV-scale) simulations are checked by performing a series of test cases, including interfacial momentum/heat/mass transport, conjugate heat/mass transfer, chemical reactions, and two practical applications containing reacting interfaces. An overall first-order convergence rate has been observed in both spatial and temporal accuracy tests. • Transport processes in porous media are modeled without empirical parameters. • The coupling between fluid and solid/porous regions is intrinsically solved in a monolithic manner. • The approach is suitable for both pore-scale and REV-scale simulations. • Various external, conjugate, and reactive transport problems are successfully solved with the approach. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolysis (PEMWE) exhibits significant promise in generating hydrogen from intermittent renewable resources. However, the performance of PEMWE at high current densities is restricted by the significant loss in mass transfer in the porous transport layer (PTL). Here, nine porosity configurations of PTLs were utilized to investigate the impact of PTL structure on the oxygen-water transport performance and mechanism in PEMWE operated at 5 A/cm2. The lattice Boltzmann model is improved by integrating the electrochemical reaction boundary condition, which can more accurately describe the mass transformation and the oxygen-expelling caused by reaction-induced pressure than the previous methods using injection boundary conditions. The results suggest that the porosity configuration does not change the capillary fingering pattern of the expelling process. The PTLs with small to large gradient porosity achieve the lowest average oxygen saturation of 0.24 in PTL and 0.39 on the catalyst layer (CL) surface. Oxygen transport from small pores to large pores releases pressure and can be accompanied by the dynamic behavior of snap-off, accelerating the expulsion of oxygen, and conversely, oxygen may be trapped in large pores and block the water transport pathway. Notably, the PTL/CL interface saturation positively correlates to the breakthrough pressure. The study can facilitate the design and development of PTL structure. • LBM model with reaction boundary is proposed for oxygen transport study. • Regional porosity regulates oxygen invasion behaviors. • Correlation between two-phase interface and oxygen transport is revealed. • Oxygen saturation on CL surface positively correlated to breakthrough pressure. • Small to large gradient porosity PTL benefits oxygen transfer. [ABSTRACT FROM AUTHOR]

CO 2 miscible flooding is a promising technique for enhancing tight oil development and achieving carbon capture, utilization, and storage. This work has developed a comprehensive pore-scale modeling workflow for CO 2 miscible flooding in tight reservoirs. Firstly, Maxwell-Stefan diffusion and equation of state are coupled to calculate Fick diffusion flux, considering composition-dependent effects. Subsequently, the Navier-Stokes and mass transport equations are coupled, incorporating crucial recovery mechanisms in miscible flooding. Furthermore, the effects of essential factors on miscible flow in tight porous media are analyzed. The findings are as follows. The competition between molecular and convective diffusion determines the displacement patterns. Both diffusion mechanisms contributed before the CO 2 breakthrough; after that, the oil retained in unswept zones was extracted by molecular diffusion and subsequently displaced by limited convection. The relative contributions of each recovery mechanism are evaluated from a pore-scale perspective. Viscosity reduction primarily affects the oil production rate, while desorption and extraction mainly influence the ultimate oil recovery. A higher Péclet number results in an earlier gas breakthrough, causing a transition from piston-like to ramified displacement, which negatively impacts oil recovery and CO 2 storage. Fracture angle and connectivity significantly affect the breakthrough moment and the recovery factor. The adsorption rate has a slight impact on the oil production rate, while the maximum adsorption capacity affects the final oil production and the stability of the miscible flooding front. • A comprehensive pore-scale modeling workflow of CO 2 miscible flooding is established. • Competition between molecular and convective diffusion determines the flow pattern. • Recovery mechanisms of CO 2 miscible flooding in tight reservoir are compared. • Pore-scale CO 2 -oil miscible flow behavior under different factors is discussed. [ABSTRACT FROM AUTHOR]

Fundamental understanding of turbulent flow and heat transfer in composite porous-fluid systems, which consists of a fluid-saturated stochastic open-cell metal foam and a flow passing over it, is crucial for fostering technological development in numerous applications such as transpiration cooling in aerospace, packed-bed thermal storage and thermal management of electronic devices. In this work, conjugate heat transfer simulations were adopted to explore the turbulent flow and heat transfer features in a composite porous-fluid system at the pore scale. Simulations were performed to account for the influence of the blockage ratios (i.e., BR = 0.5, 0.8 and 1.0) on pressure drop and heat transfer rate by introducing a new concept called penetration cooling length. Furthermore, the effect of Reynolds numbers (i.e., Re = 1800, 3600 and 7200) at different blockage ratios was investigated in terms of pressure drop, fluid and solid temperatures, interstitial heat transfer coefficient, and flow leakage. Results indicate that for a fixed blockage ratio, as the Reynolds number increases by a factor of 3.0, there is a 14.9-fold increase in the pressure drop and a 2.9-fold increase in the interstitial heat transfer coefficient. Additionally, for a fixed Reynolds number, when the blockage ratio increases by a factor of 2.0, there is a 6.8-fold increase in the pressure drop and a 1.8-fold increase in the interstitial heat transfer coefficient. Flow visualization indicated that the penetration cooling length is influenced by flow leakage from the porous-fluid interface. Results show at small blockage ratios and low Reynolds numbers, a significant portion of the flow from the porous region leaves it to the clear region on top of the porous block. While, at high Reynolds numbers and large blockage ratios, the flow leakage is reduced. Additionally, for a low blockage ratio (BR < 0.5), the amount of flow leakage depends on the Reynolds number, while it is independent of the Reynolds number for BR > 0.8. Finally, this study introduces a novel correlation for the interstitial heat transfer coefficient derived from conjugate heat transfer pore-scale simulations. The correlation is established on the basis of Reynolds number, blockage ratio, and development length of the metal foam, offering valuable insights into heat transfer phenomena in porous media. Modelling conjugate heat transfer in a composite porous-fluid system with stochastic open-cell metal foam. Simultaneous effect of blockage ratio (B R) and Reynolds number (R e) on interstitial heat transfer coefficient contour; First row: B R = 0.5; Second row: B R = 0.8; Third row: B R = 1.0. [Display omitted] • Turbulent heat transfer of flow in composite porous-fluid systems is studied. • Pore-scale conjugate heat transfer analysis is performed. • A new concept termed penetration cooling length (PCL) is introduced. • The dependency of PCL on Reynolds number (Re) and blockage ratio (BR) is studied. • For a fixed BR, if Re increases by 3.0 times, the pressure drop rises by 14.9-fold. [ABSTRACT FROM AUTHOR]

A popular equation that is often employed to represent the relationship between the pressure loss and the fluid flow in fluidized or packed granular beds is the Ergun equation, which is an extension of Darcy’s law. In this paper, the method of Smoothed Particle Hydrodynamics (SPH) is used to numerically study the flow field across a rectangular channel partially filled with a porous layer both at the Representative Elementary Volume (REV) scale using the Ergun equation and at the pore scale. Since the flow field can be estimated at the REV scale with a much lower cost compared to the pore scale, it is important to evaluate how accurately the pore-scale results can be reproduced at the REV scale. The comparison between both scales is made in terms of the velocity profiles at the outlet of the rectangular channel and the pressure losses across the clear and porous zones for three different arrays of solid grains at the pore scale. The results show that minimum differences in the flow structure and velocity profiles between the REV and the pore scale always occur at intermediate values of the porosity (ϕ=0.44 and 0.55). As the porosity increases, the differences between the REV and the pore scale also increase. The details of the pressure losses are affected by the geometry of the porous medium. In particular, we find that the pressure profiles at the REV scale match those at the pore scale almost independently of the porosity only when the grains are uniformly distributed in a non-staggered square array.

Water flooding technology is widely used to improve oil recovery efficiency in oilfields. The capillary barrier effect induced by the complex pore structures in the reservoir rocks is a crucial reason for the trapping of a great deal of residual oil in oil reservoirs after water flooding. However, the formation condition along with the effect on the recovery rate of the capillary barrier under different wettability conditions should be investigated further. To bridge the gap between the microscopic mechanism of the capillary barrier effect and the macroscopic mechanism of oil displacement efficiency, a simple conceptual capillary model is constructed to obtain the formation conditions of the capillary barrier using the analysis method, and its influence on macroscopic oil displacement efficiency in the porous media model with an opening angle of 45° is systematically investigated in this study using direct numerical simulations (DNS) coupled with the volume of fluid method. The results showed that the capillary barrier effect plays a significant role in the formation of the residual oil in the reservoir rock and the contact angle and the opening angle are the primary factors for the formation of the capillary barrier. The capillary force is the driving force when the oil–water interface advances in the throat channel under water-wet conditions, while the capillary force hinders the movement of oil–water movement when the liquid flows out of the throat channel and when θ + β > 90o. Furthermore, the highest oil displacement efficiency is achieved at the intermediate capillary number and in the case that the minimum conditions of occurrence of the capillary barrier phenomenon are satisfied. This is of great significance for controlling the optimized contact angle to further enhance the oil recovery rate of current oil reservoirs using waterflooding technology. [ABSTRACT FROM AUTHOR]

Studying the mechanisms embedded in the immiscible displacement of the two-phase fluids has many engineering and natural implications, like the CO2 geological storage, the secondary or ternary oil and gas recovery and the NAPL remediation in underground formations. The pore-scale phenomena such as Haines jump and capillary filling are recognized in the literatures to have a strong impact on the displacement phenomena. Haines jump is characterized by an abrupt jump of some certain two-phase interfaces while rearranging the configuration of the meniscus of the surrounding pores. In contrast, the capillary filling induces a flat interface movement, where non-wetting phase fluid favors the larger pores due to capillary forces, and vice versa. In this article, we have simulated the drainage process in randomly distributed pore structures with varied pore throat diameters. The Haines jump and capillary filling phenomena are recognized to play a significant role in the saturation and frontal position curves. As a result, Haines jump tends to induce a hop of frontal position given the same saturation, whereas the capillary filling evades pore spaces with a fixed frontal position. In addition, the influence of capillary number and viscosity ratio are thoroughly analyzed. The result shows that higher capillary number and higher viscosity ratio are deemed favorable for the entrapment of non-wetting phase fluid (like CO2). The energy equilibrium study shows around 48% of the external input work is dissipated through these instantaneous irreversible events. Ways to reduce the occurrence of these events will undoubtedly increase the displacement energy efficiency. This work has a direct implication for CO2 geological storage.

Wettability is an important factor controlling the displacement of immiscible fluids in porous media and therefore affects the flow and transport of supercritical (sc) CO2 in geologic carbon sequestration. Because few studies have focused on the wettability effect in scCO2-brine flow systems, we experimentally and numerically tested influences of wettability on drainage at the pore network scale. Using a high-pressure micromodel-microscopy system, we performed experiments of scCO2 invasion into brine-saturated water-wet and intermediate-wet micromodels, and recorded the scCO2 invasion morphology under reservoir relevant conditions. We also performed pore-scale numerical simulations to infer 3D details of fluid–fluid displacement processes. During drainage under intermediate-wet conditions, we found higher scCO2 saturation, wider scCO2 fingering, and more compact displacement patterns. The simulation results are qualitatively consistent with the experiments. Through quantitative analyses of the experiments, we found that the reduced wettability decreases the displacement front velocity, promotes non-wetting phase pore-filling events in the longitudinal direction, delays the breakthrough time of invading fluid, and increases the displacement efficiency. Simulated results also show that the fluid–fluid interface area follows a unified power-law relation with scCO2 saturation, and show smaller interface area in intermediate-wet case which suppresses the mass transfer between the phases. These pore-scale results provide insights for the wettability effects on CO2–brine immiscible displacement in geologic carbon sequestration.

Wettability is an important factor controlling the displacement of immiscible fluids in porous media and therefore affects the flow and transport of supercritical (sc) CO2 in geologic carbon sequestration. Because few studies have focused on the wettability effect in scCO2-brine flow systems, we experimentally and numerically tested influences of wettability on drainage at the pore network scale. Using a high-pressure micromodel-microscopy system, we performed experiments of scCO2 invasion into brine-saturated water-wet and intermediate-wet micromodels, and recorded the scCO2 invasion morphology under reservoir relevant conditions. We also performed pore-scale numerical simulations to infer 3D details of fluid–fluid displacement processes. During drainage under intermediate-wet conditions, we found higher scCO2 saturation, wider scCO2 fingering, and more compact displacement patterns. The simulation results are qualitatively consistent with the experiments. Through quantitative analyses of the experiments, we found that the reduced wettability decreases the displacement front velocity, promotes non-wetting phase pore-filling events in the longitudinal direction, delays the breakthrough time of invading fluid, and increases the displacement efficiency. Simulated results also show that the fluid–fluid interface area follows a unified power-law relation with scCO2 saturation, and show smaller interface area in intermediate-wet case which suppresses the mass transfer between the phases. These pore-scale results provide insights for the wettability effects on CO2–brine immiscible displacement in geologic carbon sequestration.

Porous media can be found in all areas of scientific life, such as medicine, civil engineering, material science, fluid dynamics. Computing has achieved high efficiency and computational capacity – so far. However, three-dimensional Computational Fluid Dynamics (CFD) simulations of microstructure remain significant challenges. Pore-scale simulations can help understand the physical processes and determine macroscopic parameters such as the high-frequency limit of dynamic tortuosity, viscous, and thermal characteristic lengths. Independent of whether the computational problem is two or three-dimensional, the geometry as input parameter must be prepared. For this reason, geometry representation methods play a crucial role in the analysis at the pore-scale, especially in numerical simulations. In this article, an insight into microstructures’ visualization capabilities is provided essentially for CFD simulations.

• The relationship between the DLVO potential energy and the physical-chemical properties. • The relationship between the particle deposition rate and energy barrier. • Relative porosity variation in the porous media coating different grain material. • The fluctuation of permeability reduction relating to bridging and bridge collapse. In this study, we investigated the effect mechanism of the grain material of artificial porous media coating quartz sand (SiO 2), titanium dioxide (n-TiO 2), zinc oxide (ZnO) and polystyrene (PS) on the motion and deposition of suspended particles. First, the relationship was deeply analysed between the DLVO potential energy and the physico-chemical properties of grain material, including the Hamaker constant and surface zeta potential. Second, the lattice Boltzmann method-immersed moving boundary-discrete element method (LBM-IMB-DEM) was used to investigate the motion characteristics of suspended particles and their effects, including the penetration rate, deposition rate, porosity reduction and the porosity-permeability relations. Third, the relations were innovatively explained between the energy barrier and the particles bridging and bridge collapse which cause the fluctuation of permeability reduction. The main results are as follows. (1) The descending order of the energy barrier between suspended particle and grain material is SiO 2 , ZnO, PS and n-TiO 2 , which is the same as that of the surface zeta potential of grain material. (2) For the suspended particles with the same size, the higher potential energy and Primary energy minimum (PEM) enhance the penetration rate. The particle deposition rate in porous media coating n-TiO 2 is higher than others. (3) The highest non-uniformity of the porosity reduction occurs in the porous media coating the material with the lowest energy barrier. (4) For the grain material with lower energy barrier, the fluctuation frequency of permeability reduction is lower owing to the longer bridging time. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolysis stands as a promising avenue for energy storage in converting renewable energy resources into hydrogen. However, the oxygen management issues at high current densities pose substantial challenges to the system's efficiency and stability. Considering that the porous transport layer (PTL) plays a crucial role in governing the countercurrent transfer of oxygen and the water supply, the impact of PTL wettability on oxygen transport is investigated through the pore-scale simulation. The lattice Boltzmann method model coupled with a reaction boundary instead of using injection boundary simplification is proposed to better describe the mass conversion and oxygen transport dynamics driven by the reaction-introduced pressure variation. The results suggest that hydrophilicity configuration affects the oxygen-water distribution and the oxygen retreat behavior after the breakthrough. Oxygen tends to accumulate in lower hydrophilicity regions. Thus, a synergism of high and low hydrophilicity on the bottom of PTL proves advantageous in reducing oxygen saturation on the CL surface. Constructing the oxygen-water separate transport pathways effectively regulates the oxygen-water distribution and reduces oxygen transport resistance, thus remarkably reducing the oxygen saturation in PTL. These findings contribute to a better understanding of oxygen transport within PTL, facilitating the further development of PTL. • LBM model coupled with reaction boundary is proposed for two-phase flow study. • Impact degree of pore structure and wettability on oxygen transport is revealed. • Higher regional PTL hydrophilia could reduce the oxygen accumulation. • Oxygen-water separately transport mode is achieved via PTL wettability design. • Oxygen-water separately transport mode reduces oxygen transport resistance. [ABSTRACT FROM AUTHOR]

Porous media have been extensively used for the enhancement of heat transfer, due to their large specific surface area. In many cases, the flow and heat transfer in porous media are also coupled with other flow patterns, such as the channel flow. This work investigates numerically a non-isothermal three-dimensional mixing process from a rectangular channel and a porous medium to reveal the influence of the structural parameters on the flow and heat transfer characteristics in the coupled system. The detailed heat and momentum transport behavior at the coupled interface are analyzed at the pore-scale. Correlations of the friction factor and the Nusselt number within the porous media are proposed as functions of the Reynolds number, porosity, velocity ratio, and pore size. Results from the pore-scale simulations are also used to improve the less-cost representative-elementary-volume-scale numerical model, which can be further used for the modeling of relevant engineering problems. [ABSTRACT FROM AUTHOR]

The combination of additive manufacturing and replication technique enables the development of new ceramic foam filters (CFFs) for the filtration of metal melts based on computer‐generated templates. This article presents a numerical study on the sensitivity of filtration performance with respect to different geometric modifications, applied to an artificial monodisperse base structure. Three different geometric modifications are implemented, namely, elliptical elongation and flattening of the strut cross section with respect to the flow direction, additional finger‐like struts protruding into the pore cavity, and addition of deliberately closed windows. All modifications are implemented for overall porosities of 70–90%. The performance of the new structures is evaluated for continuous casting of aluminum by comparing the hydraulic tortuosity, the permeability, the Forchheimer coefficient, and the filtration coefficient, which are obtained from detailed pore‐scale simulations of the melt flow and inclusions transport using an Euler–Langrange approach. For the fast determination of the permeability coefficients, a novel and extremely simple model for the prediction of the Forchheimer coefficient is described. The investigation shows that geometric modifications to open‐cell foams potentially improve the filtration performance without significant decrease in filter porosity and can be considered as templates for the design of efficient CFFs. [ABSTRACT FROM AUTHOR]

Advanced high-temperature oxidation resistance is a crucial characteristic of metallic materials in porous burners. Extreme combustion conditions could lead to oxidation-affected erosion of porous media at a long-time period of burner operation. In this paper, we numerically simulated oxide scale growth at a porous radiant burner fabricated by Ni-Al intermetallic alloy using the combustion synthesis method, focusing on the structure degradation caused by periodic oxide scale spallation. A three-dimensional geometrical model of a porous intermetallic scaffold was obtained by scanning the porous burner using the X-ray CT technique. The surface erosion was modeled by the surface reconstruction based on calculated values of spalled oxide layer thickness. The simulation revealed that the submerged flame results in non-uniform distribution of the temperature at the solid surface. Such non-isothermal conditions lead to a two-times thicker oxide scale at the external surface of the burner. Thin struts of the intermetallic scaffold are prone to oxidation-affected erosion first, which forms discontinues and further fragmentation. The porous scaffold could lose about 50% of initial weight before fragmentation under conditions with intense oxide spallation. In such large structural degradation, the average flow velocity could reduce by a factor of 3, leading to changing of flame stabilization region.

Water injection with an oscillatory pressure boundary is a promising technology, which can achieve a more economical and environment-friendly EOR (enhanced oil recovery). However, due to the unclear critical injection frequency, its oil production performance has been unstable and is far from reaching the optimal level. Here, a numerical model is established for oil recovery by the water injection with the oscillatory boundary condition to find out the critical frequency for the optimal EOR. The correlations between the water injection frequency and the EOR level at diverse oil–water surface tensions and oil viscosities are integrated into the model. Our numerical model reveals that an optimal EOR of roughly 10% is achieved at the critical water injection frequency compared with water injection without an oscillatory boundary. The EOR mechanism is revealed showing that upon water injection with the optimum frequency, the formation of the preferential pathways is inhibited and the pressure transmits to the wall sides to displace the oil. Moreover, it is indicated that the required critical frequency increases with higher surface tension and larger oil viscosity. In addition, the difference between the residual oil saturation at the optimal frequency increases with the increase in surface tension compared with water injection without an oscillatory boundary. Last but not least, it is elucidated that at a constant injection frequency, a higher EOR is achieved when the water–oil surface tension is lower but the oil viscosity is larger. Our work promises economic, eco-friendly and controllable enhanced oil recovery.

Numerical models that accurately describe the nano/microscale transport phenomena in the proton exchange membrane fuel cells (PEMFC) are highly required. In this study, a multiscale PEMFC model is developed by coupling a pore-scale model for the catalyst layer (CL) and a cell-scale model. In the pore-scale model, oxygen transport and electrochemical reaction under different platinum loadings within porous agglomerates are simulated. The pore-scale model, as a sub-grid model, is then coupled into a two-phase and non-isothermal cell-scale model. The multiscale model developed successfully predicts the impact of Platinum loading on the limiting current density, while the traditional one with the classical agglomerate model fails to. Detail distributions of important variables including concentration, current density, and saturation are discussed. Furthermore, using the multiscale model, ionomer content is optimized to improve the cell performance as well as reduce the performance loss when Pt loading is reduced. It is demonstrated that multiscale model incorporating nano/microscopic transport phenomena is promising to more accurately reveal the coupling mechanisms of multiple reactive transport processes in PEMFCs. [ABSTRACT FROM AUTHOR]

Reducing the Platinum (Pt) loading while maintaining the performance is highly desired for promoting the commercial use of proton exchange membrane fuel cells (PEMFCs). Different methods have been adopted to fabricate catalyst layers (CLs) with low Pt loading, including utilizing lower Pt/C catalysts (MA), mixing high Pt/C catalysts with bare carbon black particles (MB), and reducing CL thickness while maintaining high Pt/C ratio (MC). In this study, self-developed pore-scale model is adopted to investigate the performance of the three Pt reduction methods. It is found that MA shows the best performance while MB shows the worst. Then, effects of Pt dispersion are further explored. The results show that denser Pt sites will result in higher local oxygen flux and thus higher local transport resistance. Therefore, MA method, which shows the better Pt dispersion, leads to improved performance. Third, CLs with quasi-realistic structures are investigated. Higher tortuosity resulting from the random pores produces higher bulk resistance along the thickness direction, while MA still exhibits the best performance. Finally, improved CL structures are investigated by designing perforated CL structures. It is found that adding perforations can significantly reduce the bulk transport resistance and can improve the CL performance. It is demonstrated that CL structure plays important roles on performance, and there are still huge potentials to further improve CL performance by increasing Pt dispersion and optimizing CL structures. • Three kinds of Pt loading reduction methods are analyzed and compared in detail. • Utilizing low Pt/C catalysts when reducing Pt loading leads to high performance. • High Pt dispersion is beneficial for reducing the local transport resistance. • Adding perforations can significantly reduce the bulk transport resistance. [ABSTRACT FROM AUTHOR]

Gaseous flow through ultra-tight porous media, e.g. shale and some high-performance insulation materials, is often rarefied, invalidating an analysis by the continuum flow theory. Such rarefied flows can be accurately described by the kinetic theory of gases which utilizes the Boltzmann equation and its simplified kinetic models. While discrete velocity methods have been successful in directly solving these equations, the immense potential of a particle-based solution of the variance-reduced Boltzmann-BGK (Bhatnagar–Gross–Krook) equation for rarefied flows in porous media has not been exploited yet. Here, a parallel solver based on the low variance deviational simulation Monte Carlo method is developed for 3D flows, which enables pore-scale simulations using digital images of porous media samples. The unique advantage of this particle-based formulation is in providing additional insights regarding the multi-scale nature of the flow and surface/gas interactions via two new parameters, i.e. pore and surface activity, respectively. Together, these two parameters can identify key flow properties of the porous media. The computational efficiency and accuracy of the current method has also been analysed, suggesting that this new solver is a powerful simulation tool to quantify flow properties of ultra-tight porous media. [ABSTRACT FROM AUTHOR]

The lattice Boltzmann method (LBM) plays an important role in the study of the internal flow behavior at the pore-scale inside the electrodes of solid oxide fuel cells (SOFCs). Porosity, tortuosity, and particle size have a remarkable effect on gas transport and electrocatalytic processes, determining the performance of cells when SOFCs are applied in electric power generation, energy storage systems, and industrial production in recent years. However, these pore-scale transport progresses are not well characterized in the numerical studies of conventional computational fluid dynamics (CFD), thus modeling with LBM at the pore-scale is an effective tool for simulating gas transport and electrochemical reactions in electrodes. It overcomes the drawbacks of experimental techniques that do not characterize these processes accurately enough and detail the distribution of important variables. In this review, the methodology and process of electrode pore-scale modeling are presented, along with the application and current studies of LBM for diffusion, electrochemical reactions, and ion migration in SOFC porous electrodes. Important results are discussed. Finally, future perspectives on pore-scale studies of porous electrodes are given. This in-depth review intends to provide ideas for the development and further application of LBM in porous SOFC electrodes. • Different electrode reconstruction methods are classified into six categories. • The modeling process and application fields of LB method are reviewed. • A detailed transfer process analysis of SOFC inside using the LB method is presented. • The future prospects of LB modeling and reconstruction methods are discussed. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolysis (PEMWE) shows great potential in coupling fluctuating renewable energy for hydrogen production. In PEMWE, the counter-current transport of oxygen in the porous transport layer (PTL) limits the process of water reaching the catalyst layer (CL), significantly affecting the performance and stability of PEMWE. Herein, a lattice Boltzmann model coupled with a reaction boundary is proposed to consider the mechanism of oxygen expelling due to increased pressure. The model is adopted to study the influence of PTL and CL hydrophilia on the mechanism and pattern of oxygen transport. The results suggest that the PTL hydrophilia results in three different flow patterns before the oxygen breakthrough occurs. After the oxygen breakthrough, the extent of oxygen retreatment is also affected by PTL hydrophilia. Increasing PTL hydrophilia can reduce the oxygen saturation within the PTL, but may increase the saturation on the CL surface. A significant decrease in oxygen saturation at the CL surface can be achieved by increasing the hydrophilia of the CL, and even a minor increase in hydrophilia from 74.5° to 54.9° can lead to a reduction of up to 50 % in oxygen saturation. These findings have implications for rationally designing PTL structures. • An LBM model with reaction boundary is developed for oxygen transport study. • Correlation between PTL/CL hydrophilia and oxygen transport is revealed. • PTL/CL hydrophilia results in three oxygen flow patterns before breakthrough. • Appropriate CL hydrophilia alleviates oxygen coverage on CL surface. • High PTL/CL hydrophilia promote oxygen expulsion. [ABSTRACT FROM AUTHOR]

Understanding the transport mechanism in catalyst layer (CL) agglomerates is crucial to enhance Pt utilization and overall fuel cell performance. In this study, high-resolution porous agglomerates are stochastically reconstructed, and capillary condensation of water in agglomerates is directly simulated using a lattice Boltzmann pseudopotential model. On this basis, a pore-scale electrochemical model is developed to investigate the effects of agglomerate structure and operating humidity on local transport resistance and agglomerate effectiveness at different Pt loadings. The results reveal that liquid water formed above 70%RH improves the electrochemical surface area (ECSA) of agglomerates with low ionomer content. An optimum I/C of 0.4 in agglomerates is determined by balancing the activated ECSA and oxygen transport resistance. Through the comparison of local transport resistance with limiting current data, an additional oxygen dissolution resistance of 60–350 s m−1 at the pore/ionomer or ionomer/Pt interface is quantified. The lowest local transport resistance of the agglomerate is achieved at about 70%RH, while condensed water at higher humidities hampers oxygen diffusion within the agglomerate, leading to reduced Pt utilization. Agglomerate size significantly affects the local transport resistance only when excessive ionomer or liquid water severely blocks primary pores. Finally, a novel multiscale coupling strategy integrating the porous agglomerate sub-model with a continuous-scale CL model is proposed, offering innovative insights into comprehending the relationship between CL structure and the performance of proton exchange membrane fuel cells. • High-resolution porous structures of the agglomerate are reconstructed. • Quantify the interfacial dissolute resistance and permeability reduction of ionomer. • Condensed water formed above 70%RH degrades the oxygen diffusion process. • Agglomerate size affects the transport resistance when primary pores are blocked. • A multiscale coupling strategy for the pore-scale agglomerate model is proposed. [ABSTRACT FROM AUTHOR]

Water flooding technology is widely used to improve oil recovery efficiency in oilfields. The capillary barrier effect induced by the complex pore structures in the reservoir rocks is a crucial reason for the trapping of a great deal of residual oil in oil reservoirs after water flooding. However, the formation condition along with the effect on the recovery rate of the capillary barrier under different wettability conditions should be investigated further. To bridge the gap between the microscopic mechanism of the capillary barrier effect and the macroscopic mechanism of oil displacement efficiency, a simple conceptual capillary model is constructed to obtain the formation conditions of the capillary barrier using the analysis method, and its influence on macroscopic oil displacement efficiency in the porous media model with an opening angle of 45° is systematically investigated in this study using direct numerical simulations (DNS) coupled with the volume of fluid method. The results showed that the capillary barrier effect plays a significant role in the formation of the residual oil in the reservoir rock and the contact angle and the opening angle are the primary factors for the formation of the capillary barrier. The capillary force is the driving force when the oil–water interface advances in the throat channel under water-wet conditions, while the capillary force hinders the movement of oil–water movement when the liquid flows out of the throat channel and when θ + β > 90o. Furthermore, the highest oil displacement efficiency is achieved at the intermediate capillary number and in the case that the minimum conditions of occurrence of the capillary barrier phenomenon are satisfied. This is of great significance for controlling the optimized contact angle to further enhance the oil recovery rate of current oil reservoirs using waterflooding technology.

The process of fluid displacement in a microscale of porous media in oil reservoirs rock is affected by several factors. Understanding the effects of factors in multiphase flow mechanisms in porous media through numerical investigations allows us to estimate the flow behavior. In this study, the effect of important parameters like viscosity ratio and velocity on displacement in porous media was investigated using the volume of fluid method as a numerical model. So, a set of governing equations were calculated under a wide range of injection velocities and viscosity ratios to characterize displacing pattern. A similar experiment was done on a micromodel to validate the numerical method, and a rational agreement was reached between the experimental and numerical results. Saturation, velocity, pressure, breakthrough times, displacement efficiencies and displacement patterns were studied. Results show that the effect of viscosity ratio is more important than the effect of velocity. If the viscosity ratio increases five times, injection rate has to decrease 10 times to recover the same amount of oil. However, in a homogeneous porous media, fingering takes place due to the interaction of some forces where in a heavy oil reservoir the viscous forces play the main role. Also, pore scale events were investigated to better understanding the role of film rupture, coalescence, pinch off and splitting in meniscus displacement through the throat of the pore. [ABSTRACT FROM AUTHOR]

We study the impact of pore space heterogeneity on mixing and reaction in porous media. We simulate the parallel injection of two streams of reactants at different pH in a three‐dimensional microporous consolidated rock whose pore space was resolved by differential micro‐CT imaging. As an exemplar of a heterogeneous medium, we consider the pore structure obtained from a Portland carbonate sample. We use direct numerical simulation to study the coupled impact of flow heterogeneity, characterized by a wide distribution of velocities and chemical reversibility on multispecies reaction. The flow field is found from the Darcy‐Brinkman equation while the advection‐diffusion equation describes transport, which is coupled to a general multispecies geochemical solver for homogeneous reactions; precipitation, and dissolution are ignored. We observe a highly nonuniform spatial distribution of concentration and rates of formation and consumption. For advection‐dominated transport, the heterogeneous flow field leads to significant transverse mixing in macropores at early times, followed by a slower mixing driven by diffusion between macropore and micropore regions. The effective rates of formation and consumption are species‐dependent and distinct in macroporosity and microporosity: while some species reach an asymptotic rate in well‐mixed regions, others still show a transient nonmonotonic behavior as a consequence of incomplete mixing. Our findings have important implications for the understanding of time‐ and space‐dependent reaction rate behavior: the coupled impact of pore space heterogeneity and reversible reactions need to be taken into account as key determinants to describe multispecies reactive transport. Key Points: Reactive behavior is simultaneously influenced by pore space heterogeneity, multispecies reactive transport, and reaction reversibilityThe evolution of rates of formation and consumption is species‐dependent and highly distinct in macroporosity and microporosityWell‐mixed regions result in asymptotic rates; incomplete mixing leads to transient and, for some species, even nonmonotonic behavior [ABSTRACT FROM AUTHOR]

Geoelectrical methods are broadly used in earth sciences for various purposes. To correctly interpret field geoelectrical data, it is essential to have a mechanistic understanding of the effective electrical conductivity and permittivity of geological materials over a broad frequency range. Recently, the pore‐scale numerical simulation, which utilizes the digital microstructural images of the material, has become a powerful tool in studying the effective electrical properties of geological media. However, it is still difficult to incorporate surface‐related electrochemical processes in a pore‐scale simulation. In this study, we develop a general framework to consider these electrochemical processes in pore‐scale simulations, which enable the calculation of broadband effective electrical conductivity and permittivity of porous geological media. A Berea sandstone sample is utilized to demonstrate the use of the proposed framework. Laboratory experiments of the effective electrical conductivity and permittivity of the sample in the frequency range from 10−3 to 109 Hz provided valuable measurement data for validating the simulation. The good agreement between our simulated spectra and the experimental data provides validation for the numerical simulation to reproduce the variations in the effective electrical conductivity and permittivity of porous geological materials induced by both the electrochemical polarizations and the interfacial polarization. This work thus provides a useful tool for studying the effective electrical properties of porous geological materials featuring complex microstructures. Key Points: A framework is developed for the pore‐scale numerical simulation of broadband effective electrical properties of porous mediaBoth the interfacial polarization and the electrochemical polarizations are considered in the simulationA Berea sandstone sample is utilized to demonstrate the use of the framework [ABSTRACT FROM AUTHOR]