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Qinjun Kang - One of the best experts on this subject based on the ideXlab platform.

  • Pore Scale study of Pore ionomer interfacial reactive transport processes in proton exchange membrane fuel cell catalyst layer
    Chemical Engineering Journal, 2020
    Co-Authors: Li Chen, Qinjun Kang, Ruiyuan Zhang, Wen-quan Tao
    Abstract:

    Abstract Understanding interactions between constituent distributions and reactive transport processes in catalyst layer (CL) of proton exchange membrane fuel cell is crucial for improving cell performance and reducing cell cost. In this study, high-resolution porous structures of cathode CL are reconstructed, where all the constituents in CLs are resolved. A Pore-Scale model based on the lattice Boltzmann method is developed for oxygen diffusion in Pores and ionomer, as well as electrochemical reaction at the Pt surfaces. Particularly the model considers the Pore-ionomer interfacial transport processes with distinct characteristics of sharp concentration drop, large diffusivity ratio and interfacial dissolution reaction. After validated by interfacial transport processes with analytical solutions, the Pore-Scale model is applied to reactive transport processes inside complex CL nanoScale structures. Pore-Scale results reveal that Pore-ionomer interfacial transport processes generate extremely high local transport resistance, significantly reducing the total reaction rate. As volume fraction of carbon increases, the value of the optimum ionomer content generating the best cell performance decreases, while the value of the optimum ionomer content resulting in the lowest performance loss under low Pt loading reduces. The two values generally are different. The Pore-Scale model helps to understand reactive transport processes and to optimize the CL structures.

  • comprehensive comparison of Pore Scale models for multiphase flow in porous media
    Proceedings of the National Academy of Sciences of the United States of America, 2019
    Co-Authors: Benzhong Zhao, Christopher W Macminn, Bauyrzhan Primkulov, Yu Chen, Albert J Valocchi, Jianlin Zhao, Qinjun Kang, Kelsey Bruning, James E Mcclure, Cass T Miller
    Abstract:

    Multiphase flows in porous media are important in many natural and industrial processes. Pore-Scale models for multiphase flows have seen rapid development in recent years and are becoming increasingly useful as predictive tools in both academic and industrial applications. However, quantitative comparisons between different Pore-Scale models, and between these models and experimental data, are lacking. Here, we perform an objective comparison of a variety of state-of-the-art Pore-Scale models, including lattice Boltzmann, stochastic rotation dynamics, volume-of-fluid, level-set, phase-field, and Pore-network models. As the basis for this comparison, we use a dataset from recent microfluidic experiments with precisely controlled Pore geometry and wettability conditions, which offers an unprecedented benchmarking opportunity. We compare the results of the 14 participating teams both qualitatively and quantitatively using several standard metrics, such as fractal dimension, finger width, and displacement efficiency. We find that no single method excels across all conditions and that thin films and corner flow present substantial modeling and computational challenges.

  • Pore Scale study of reactive transport processes in catalyst layer agglomerates of proton exchange membrane fuel cells
    Electrochimica Acta, 2019
    Co-Authors: Li Chen, Qinjun Kang, Wen-quan Tao
    Abstract:

    Abstract Porous structures of agglomerates in cathode catalyst layers (CLs) of proton exchange membrane fuel cells are reconstructed, in which all the four phases are resolved including Platinum, carbon, ionomer and Pore. A Pore-Scale reactive transport model based on the lattice Boltzmann method is developed, in which oxygen dissolution reaction at Pore-ionomer interface, oxygen diffusion inside ionomer, and electrochemical reaction at ionomer-Pt interface are considered. Emphasis is put on structural parameters, especially Pt/C mass ratio, on the reactive transport process and the volumetric reaction rate (or current density). Pore-Scale results show that while under high Pt loading oxygen is depleted quite close to the surface of the spherical agglomerate, it has to penetrate deep into the porous agglomerate before it is completely consumed under low Pt loading which is not captured by classical agglomerate model based on homogeneous mixture assumption. Pore-Scale results also found that effects of transport inside the agglomerate decreases as reaction rate, porosity or ionomer thickness increases. Finally, local transport resistance inside the agglomerate is evaluated, and it increases as the agglomerate size increases or the dissolution reaction rate decreases.

  • Pore Scale study of multiphase multicomponent reactive transport during co2 dissolution trapping
    Advances in Water Resources, 2018
    Co-Authors: Li Chen, Qinjun Kang, Mengyi Wang, Wen-quan Tao
    Abstract:

    Abstract Solubility trapping is crucial for permanent CO2 sequestration in deep saline aquifers. For the first time, a Pore-Scale numerical method is developed to investigate coupled scCO2-water two-phase flow, multicomponent (CO2(aq), H+, HCO3−, CO32− and OH−) mass transport, heterogeneous interfacial dissolution reaction, and homogeneous dissociation reactions. Pore-Scale details of evolutions of multiphase distributions and concentration fields are presented and discussed. Time evolutions of several variables including averaged CO2(aq) concentration, scCO2 saturation, and pH value are analyzed. Specific interfacial length, an important variable which cannot be determined but is required by continuum models, is investigated in detail. Mass transport coefficient or efficient dissolution rate is also evaluated. The Pore-Scale results show strong non-equilibrium characteristics during solubility trapping due to non-uniform distributions of multiphase as well as slow mass transport process. Complicated coupling mechanisms between multiphase flow, mass transport and chemical reactions are also revealed. Finally, effects of wettability are also studied. The Pore-Scale studies provide deep understanding of non-linear non-equilibrium multiple physicochemical processes during CO2 solubility trapping processes, and also allow to quantitatively predict some important empirical relationships, such as saturation-interfacial surface area, for continuum models.

  • Pore Scale study of multiphase reactive transport in fibrous electrodes of vanadium redox flow batteries
    Electrochimica Acta, 2017
    Co-Authors: Li Chen, Wen-quan Tao, Piotr Zelenay, Rangachary Mukundan, Qinjun Kang
    Abstract:

    Abstract The electrode of a vanadium redox flow battery generally is a carbon fibre-based porous medium, in which important physicochemical processes occur. In this work, Pore-Scale simulations are performed to study complex multiphase flow and reactive transport in the electrode by using the lattice Boltzmann method (LBM). Four hundred fibrous electrodes with different fibre diameters and porosities are reconstructed. Both the permeability and diffusivity of the reconstructed electrodes are predicted and compared with empirical relationships in the literature. Reactive surface area of the electrodes is also evaluated and it is found that existing empirical relationship overestimates the reactive surface under lower porosities. Further, a Pore-Scale electrochemical reaction model is developed to study the effects of fibre diameter and porosity on electrolyte flow, VII/VIII transport, and electrochemical reaction at the electrolyte-fibre surface. Finally, evolution of bubble cluster generated by the side reaction is studied by adopting a LB multiphase flow model. Effects of porosity, fibre diameter, gas saturation and solid surface wettability on average bubble diameter and reduction of reactive surface area due to coverage of bubbles on solid surface are investigated in detail. It is found that gas coverage ratio is always lower than that adopted in the continuum model in the literature. The current Pore-Scale studies successfully reveal the complex multiphase flow and reactive transport processes in the electrode, and the simulation results can be further upScaled to improve the accuracy of the current continuum-Scale models.

Li Chen - One of the best experts on this subject based on the ideXlab platform.

  • Pore-Scale modeling of complex transport phenomena in porous media
    'Elsevier BV', 2022
    Co-Authors: Li Chen, Zhao Jianlin, Kang Qinjun, Li Zeng-yao, Carmeliet Jan, Shikazono Naoki, Tao Wen-quan
    Abstract:

    Porous media play important roles in a wide range of scientific and engineering problems. Recently, with their increasing application in energy conversion and storage devices, such as fuel cells, batteries and supercapacitors, it has been realized that transport processes and reactions occurring in the Pores and at the interfaces of different constituents significantly affect the performance of the porous media, yet these Pore-Scale transport phenomena are not well described or even neglected in the conventional numerical models based on the representative element volume (REV). Pore-Scale modeling is an efficient tool for the simulation of Pore-Scale transport and reactions in porous media because of its ability to accurately characterize these processes and to provide the distribution details of important variables which are challenging for current experimental techniques to provide either due to lack of in-situ measurement capability or due to the limited spatial and temporal resolution. In the present review, the advances and challenges of the state-of-the-art Pore-Scale modeling are summarized. The practical applications of Pore-Scale modeling in the fields of geoscience, polymer exchange membrane fuel cells (PEMFC) and solid oxide fuel cells (SOFC) are discussed. Notable results from the Pore-Scale modeling are presented, and the challenges facing the Pore-Scale model development are discussed. This in-depth review is intended to give a well-rounded introduction of critical aspects on which the Pore-Scale modeling can shed light in the development of relevant scientific and engineering systems.ISSN:0360-1285ISSN:0360-320

  • Pore Scale study of Pore ionomer interfacial reactive transport processes in proton exchange membrane fuel cell catalyst layer
    Chemical Engineering Journal, 2020
    Co-Authors: Li Chen, Qinjun Kang, Ruiyuan Zhang, Wen-quan Tao
    Abstract:

    Abstract Understanding interactions between constituent distributions and reactive transport processes in catalyst layer (CL) of proton exchange membrane fuel cell is crucial for improving cell performance and reducing cell cost. In this study, high-resolution porous structures of cathode CL are reconstructed, where all the constituents in CLs are resolved. A Pore-Scale model based on the lattice Boltzmann method is developed for oxygen diffusion in Pores and ionomer, as well as electrochemical reaction at the Pt surfaces. Particularly the model considers the Pore-ionomer interfacial transport processes with distinct characteristics of sharp concentration drop, large diffusivity ratio and interfacial dissolution reaction. After validated by interfacial transport processes with analytical solutions, the Pore-Scale model is applied to reactive transport processes inside complex CL nanoScale structures. Pore-Scale results reveal that Pore-ionomer interfacial transport processes generate extremely high local transport resistance, significantly reducing the total reaction rate. As volume fraction of carbon increases, the value of the optimum ionomer content generating the best cell performance decreases, while the value of the optimum ionomer content resulting in the lowest performance loss under low Pt loading reduces. The two values generally are different. The Pore-Scale model helps to understand reactive transport processes and to optimize the CL structures.

  • Pore Scale study of reactive transport processes in catalyst layer agglomerates of proton exchange membrane fuel cells
    Electrochimica Acta, 2019
    Co-Authors: Li Chen, Qinjun Kang, Wen-quan Tao
    Abstract:

    Abstract Porous structures of agglomerates in cathode catalyst layers (CLs) of proton exchange membrane fuel cells are reconstructed, in which all the four phases are resolved including Platinum, carbon, ionomer and Pore. A Pore-Scale reactive transport model based on the lattice Boltzmann method is developed, in which oxygen dissolution reaction at Pore-ionomer interface, oxygen diffusion inside ionomer, and electrochemical reaction at ionomer-Pt interface are considered. Emphasis is put on structural parameters, especially Pt/C mass ratio, on the reactive transport process and the volumetric reaction rate (or current density). Pore-Scale results show that while under high Pt loading oxygen is depleted quite close to the surface of the spherical agglomerate, it has to penetrate deep into the porous agglomerate before it is completely consumed under low Pt loading which is not captured by classical agglomerate model based on homogeneous mixture assumption. Pore-Scale results also found that effects of transport inside the agglomerate decreases as reaction rate, porosity or ionomer thickness increases. Finally, local transport resistance inside the agglomerate is evaluated, and it increases as the agglomerate size increases or the dissolution reaction rate decreases.

  • Pore Scale study of multiphase multicomponent reactive transport during co2 dissolution trapping
    Advances in Water Resources, 2018
    Co-Authors: Li Chen, Qinjun Kang, Mengyi Wang, Wen-quan Tao
    Abstract:

    Abstract Solubility trapping is crucial for permanent CO2 sequestration in deep saline aquifers. For the first time, a Pore-Scale numerical method is developed to investigate coupled scCO2-water two-phase flow, multicomponent (CO2(aq), H+, HCO3−, CO32− and OH−) mass transport, heterogeneous interfacial dissolution reaction, and homogeneous dissociation reactions. Pore-Scale details of evolutions of multiphase distributions and concentration fields are presented and discussed. Time evolutions of several variables including averaged CO2(aq) concentration, scCO2 saturation, and pH value are analyzed. Specific interfacial length, an important variable which cannot be determined but is required by continuum models, is investigated in detail. Mass transport coefficient or efficient dissolution rate is also evaluated. The Pore-Scale results show strong non-equilibrium characteristics during solubility trapping due to non-uniform distributions of multiphase as well as slow mass transport process. Complicated coupling mechanisms between multiphase flow, mass transport and chemical reactions are also revealed. Finally, effects of wettability are also studied. The Pore-Scale studies provide deep understanding of non-linear non-equilibrium multiple physicochemical processes during CO2 solubility trapping processes, and also allow to quantitatively predict some important empirical relationships, such as saturation-interfacial surface area, for continuum models.

  • Pore Scale study of multiphase reactive transport in fibrous electrodes of vanadium redox flow batteries
    Electrochimica Acta, 2017
    Co-Authors: Li Chen, Wen-quan Tao, Piotr Zelenay, Rangachary Mukundan, Qinjun Kang
    Abstract:

    Abstract The electrode of a vanadium redox flow battery generally is a carbon fibre-based porous medium, in which important physicochemical processes occur. In this work, Pore-Scale simulations are performed to study complex multiphase flow and reactive transport in the electrode by using the lattice Boltzmann method (LBM). Four hundred fibrous electrodes with different fibre diameters and porosities are reconstructed. Both the permeability and diffusivity of the reconstructed electrodes are predicted and compared with empirical relationships in the literature. Reactive surface area of the electrodes is also evaluated and it is found that existing empirical relationship overestimates the reactive surface under lower porosities. Further, a Pore-Scale electrochemical reaction model is developed to study the effects of fibre diameter and porosity on electrolyte flow, VII/VIII transport, and electrochemical reaction at the electrolyte-fibre surface. Finally, evolution of bubble cluster generated by the side reaction is studied by adopting a LB multiphase flow model. Effects of porosity, fibre diameter, gas saturation and solid surface wettability on average bubble diameter and reduction of reactive surface area due to coverage of bubbles on solid surface are investigated in detail. It is found that gas coverage ratio is always lower than that adopted in the continuum model in the literature. The current Pore-Scale studies successfully reveal the complex multiphase flow and reactive transport processes in the electrode, and the simulation results can be further upScaled to improve the accuracy of the current continuum-Scale models.

Wen-quan Tao - One of the best experts on this subject based on the ideXlab platform.

  • Pore Scale study of Pore ionomer interfacial reactive transport processes in proton exchange membrane fuel cell catalyst layer
    Chemical Engineering Journal, 2020
    Co-Authors: Li Chen, Qinjun Kang, Ruiyuan Zhang, Wen-quan Tao
    Abstract:

    Abstract Understanding interactions between constituent distributions and reactive transport processes in catalyst layer (CL) of proton exchange membrane fuel cell is crucial for improving cell performance and reducing cell cost. In this study, high-resolution porous structures of cathode CL are reconstructed, where all the constituents in CLs are resolved. A Pore-Scale model based on the lattice Boltzmann method is developed for oxygen diffusion in Pores and ionomer, as well as electrochemical reaction at the Pt surfaces. Particularly the model considers the Pore-ionomer interfacial transport processes with distinct characteristics of sharp concentration drop, large diffusivity ratio and interfacial dissolution reaction. After validated by interfacial transport processes with analytical solutions, the Pore-Scale model is applied to reactive transport processes inside complex CL nanoScale structures. Pore-Scale results reveal that Pore-ionomer interfacial transport processes generate extremely high local transport resistance, significantly reducing the total reaction rate. As volume fraction of carbon increases, the value of the optimum ionomer content generating the best cell performance decreases, while the value of the optimum ionomer content resulting in the lowest performance loss under low Pt loading reduces. The two values generally are different. The Pore-Scale model helps to understand reactive transport processes and to optimize the CL structures.

  • Pore Scale study of reactive transport processes in catalyst layer agglomerates of proton exchange membrane fuel cells
    Electrochimica Acta, 2019
    Co-Authors: Li Chen, Qinjun Kang, Wen-quan Tao
    Abstract:

    Abstract Porous structures of agglomerates in cathode catalyst layers (CLs) of proton exchange membrane fuel cells are reconstructed, in which all the four phases are resolved including Platinum, carbon, ionomer and Pore. A Pore-Scale reactive transport model based on the lattice Boltzmann method is developed, in which oxygen dissolution reaction at Pore-ionomer interface, oxygen diffusion inside ionomer, and electrochemical reaction at ionomer-Pt interface are considered. Emphasis is put on structural parameters, especially Pt/C mass ratio, on the reactive transport process and the volumetric reaction rate (or current density). Pore-Scale results show that while under high Pt loading oxygen is depleted quite close to the surface of the spherical agglomerate, it has to penetrate deep into the porous agglomerate before it is completely consumed under low Pt loading which is not captured by classical agglomerate model based on homogeneous mixture assumption. Pore-Scale results also found that effects of transport inside the agglomerate decreases as reaction rate, porosity or ionomer thickness increases. Finally, local transport resistance inside the agglomerate is evaluated, and it increases as the agglomerate size increases or the dissolution reaction rate decreases.

  • Pore Scale study of multiphase multicomponent reactive transport during co2 dissolution trapping
    Advances in Water Resources, 2018
    Co-Authors: Li Chen, Qinjun Kang, Mengyi Wang, Wen-quan Tao
    Abstract:

    Abstract Solubility trapping is crucial for permanent CO2 sequestration in deep saline aquifers. For the first time, a Pore-Scale numerical method is developed to investigate coupled scCO2-water two-phase flow, multicomponent (CO2(aq), H+, HCO3−, CO32− and OH−) mass transport, heterogeneous interfacial dissolution reaction, and homogeneous dissociation reactions. Pore-Scale details of evolutions of multiphase distributions and concentration fields are presented and discussed. Time evolutions of several variables including averaged CO2(aq) concentration, scCO2 saturation, and pH value are analyzed. Specific interfacial length, an important variable which cannot be determined but is required by continuum models, is investigated in detail. Mass transport coefficient or efficient dissolution rate is also evaluated. The Pore-Scale results show strong non-equilibrium characteristics during solubility trapping due to non-uniform distributions of multiphase as well as slow mass transport process. Complicated coupling mechanisms between multiphase flow, mass transport and chemical reactions are also revealed. Finally, effects of wettability are also studied. The Pore-Scale studies provide deep understanding of non-linear non-equilibrium multiple physicochemical processes during CO2 solubility trapping processes, and also allow to quantitatively predict some important empirical relationships, such as saturation-interfacial surface area, for continuum models.

  • Pore Scale study of multiphase reactive transport in fibrous electrodes of vanadium redox flow batteries
    Electrochimica Acta, 2017
    Co-Authors: Li Chen, Wen-quan Tao, Piotr Zelenay, Rangachary Mukundan, Qinjun Kang
    Abstract:

    Abstract The electrode of a vanadium redox flow battery generally is a carbon fibre-based porous medium, in which important physicochemical processes occur. In this work, Pore-Scale simulations are performed to study complex multiphase flow and reactive transport in the electrode by using the lattice Boltzmann method (LBM). Four hundred fibrous electrodes with different fibre diameters and porosities are reconstructed. Both the permeability and diffusivity of the reconstructed electrodes are predicted and compared with empirical relationships in the literature. Reactive surface area of the electrodes is also evaluated and it is found that existing empirical relationship overestimates the reactive surface under lower porosities. Further, a Pore-Scale electrochemical reaction model is developed to study the effects of fibre diameter and porosity on electrolyte flow, VII/VIII transport, and electrochemical reaction at the electrolyte-fibre surface. Finally, evolution of bubble cluster generated by the side reaction is studied by adopting a LB multiphase flow model. Effects of porosity, fibre diameter, gas saturation and solid surface wettability on average bubble diameter and reduction of reactive surface area due to coverage of bubbles on solid surface are investigated in detail. It is found that gas coverage ratio is always lower than that adopted in the continuum model in the literature. The current Pore-Scale studies successfully reveal the complex multiphase flow and reactive transport processes in the electrode, and the simulation results can be further upScaled to improve the accuracy of the current continuum-Scale models.

  • Pore Scale simulation of multicomponent multiphase reactive transport with dissolution and precipitation
    International Journal of Heat and Mass Transfer, 2015
    Co-Authors: Qinjun Kang, Li Chen, Bruce A Robinson, Qing Tang, Wen-quan Tao
    Abstract:

    Abstract Multicomponent multiphase reactive transport processes with dissolution–precipitation are widely encountered in energy and environment systems. A Pore-Scale two-phase multi-mixture model based on the lattice Boltzmann method (LBM) is developed for such complex transport processes, where each phase is considered as a mixture of miscible components in it. The liquid–gas fluid flow with large density ratio is simulated using the multicomponent multiphase pseudo-potential LB model; the transport of certain solute in the corresponding solvent is solved using the mass transport LB model; and the dynamic evolutions of the liquid–solid interface due to dissolution–precipitation are captured by an interface tracking scheme. The model developed can predict coupled multiple physicochemical processes including multiphase flow, multicomponent mass transport, homogeneous reactions in the bulk fluid and heterogeneous dissolution–precipitation reactions at the fluid–solid interface, and dynamic evolution of the solid matrix geometries at the Pore-Scale. The model is then applied to a physicochemical system encountered in shale gas/oil industry involving multiphase flow, multicomponent reactive transport and dissolution–precipitation, with several reactions whose rates can be several orders of magnitude different at a given temperature. The Pore-Scale phenomena and complex interaction between different sub-processes are investigated and discussed in detail.

Albert J Valocchi - One of the best experts on this subject based on the ideXlab platform.

  • comprehensive comparison of Pore Scale models for multiphase flow in porous media
    Proceedings of the National Academy of Sciences of the United States of America, 2019
    Co-Authors: Benzhong Zhao, Christopher W Macminn, Bauyrzhan Primkulov, Yu Chen, Albert J Valocchi, Jianlin Zhao, Qinjun Kang, Kelsey Bruning, James E Mcclure, Cass T Miller
    Abstract:

    Multiphase flows in porous media are important in many natural and industrial processes. Pore-Scale models for multiphase flows have seen rapid development in recent years and are becoming increasingly useful as predictive tools in both academic and industrial applications. However, quantitative comparisons between different Pore-Scale models, and between these models and experimental data, are lacking. Here, we perform an objective comparison of a variety of state-of-the-art Pore-Scale models, including lattice Boltzmann, stochastic rotation dynamics, volume-of-fluid, level-set, phase-field, and Pore-network models. As the basis for this comparison, we use a dataset from recent microfluidic experiments with precisely controlled Pore geometry and wettability conditions, which offers an unprecedented benchmarking opportunity. We compare the results of the 14 participating teams both qualitatively and quantitatively using several standard metrics, such as fractal dimension, finger width, and displacement efficiency. We find that no single method excels across all conditions and that thin films and corner flow present substantial modeling and computational challenges.

  • a hybrid Pore Scale and continuum Scale model for solute diffusion reaction and biofilm development in porous media
    Water Resources Research, 2015
    Co-Authors: Youneng Tang, Charles J. Werth, Albert J Valocchi
    Abstract:

    It is a challenge to upScale solute transport in porous media for multispecies bio-kinetic reactions because of incomplete mixing within the elementary volume and because biofilm growth can change porosity and affect Pore-Scale flow and diffusion. To address this challenge, we present a hybrid model that couples Pore-Scale subdomains to continuum-Scale subdomains. While the Pore-Scale subdomains involving significant biofilm growth and reaction are simulated using Pore-Scale equations, the other subdomains are simulated using continuum-Scale equations to save computational time. The Pore-Scale and continuum-Scale subdomains are coupled using a mortar method to ensure continuity of solute concentration and flux at the interfaces. We present results for a simplified two-dimensional system, neglect advection, and use dual Monod kinetics for solute utilization and biofilm growth. The results based on the hybrid model are consistent with the results based on a Pore-Scale model for three test cases that cover a wide range of Damkohler (Da = reaction rate/diffusion rate) numbers for both homogeneous (spatially periodic) and heterogeneous Pore structures. We compare results from the hybrid method with an upScaled continuum model and show that the latter is valid only for cases of small Damkohler numbers, consistent with other results reported in the literature.

  • lattice boltzmann based approaches for Pore Scale reactive transport
    Reviews in Mineralogy & Geochemistry, 2015
    Co-Authors: Hongkyu Yoon, Qinjun Kang, Albert J Valocchi
    Abstract:

    Important geoscience and environmental applications such as geologic carbon storage, environmental remediation, and unconventional oil and gas recovery are best understood in the context of reactive flow and multicomponent transport in the subsurface environment. The coupling of chemical and microbiological reactions with hydrological and mechanical processes can lead to complex behaviors across an enormous range of spatial and temporal Scales. These coupled responses are also strongly influenced by the heterogeneity and anisotropy of the geologic formations. Reactive transport processes can change the Pore morphology at the Pore Scale, thereby leading to nonlinear interactions with advective and diffusive transport, which can strongly influence larger-Scale properties such as permeability and dispersion. Therefore, one of the greatest research challenges is to improve our ability to predict these processes across Scales (DOE 2007). The development of Pore-Scale experimental and modeling methods to study reactive processes involving mineral precipitation and dissolution, and biofilm dynamics allows more fundamental investigation of physical behavior so that more accurate and robust upScaled constitutive models can be developed for the continuum Scale. A Pore-Scale model provides fundamental mechanistic explanations of how biogeochemical processes and Pore-Scale interfacial reactions alter flow paths by Pore plugging (and dissolving) under different geochemical compositions and Pore configurations. For example, dissolved CO2 during geological CO2 storage may react with minerals in fractured rocks, confined aquifers, or faults, resulting in cementation (and/or dissolution) and altering hydrodynamics of reactive flow. This can be observed in a natural analogue where primary porosity in sandstone is cemented by carbonate precipitates, affecting dissolved CO2 flow paths at the Little Garde Wash Fault, Utah (e.g., Fig. 1a–b). Several other examples demonstrating macroscopic characteristics of calcium carbonate (CaCO3) precipitation in Figure 1 include an elongated concretion along the groundwater flow direction, CaCO3 precipitation along the vertical pathway sealed …

  • using dispersivity values to quantify the effects of Pore Scale flow focusing on enhanced reaction along a transverse mixing zone
    Advances in Water Resources, 2010
    Co-Authors: Thomas Willingham, Charles J. Werth, Mart Oostrom, Albert J Valocchi, Changyong Zhang, Thomas W Wietsma
    Abstract:

    Abstract A key challenge for predictive modeling of transverse mixing and reaction of solutes in groundwater is to determine values of transverse dispersivity ( α T ) in heterogeneous flow fields that accurately describe mixing and reaction at the Pore Scale. We evaluated the effects of flow focusing in high permeability zones on mixing enhancement using experimental micromodel flow cells and Pore-Scale lattice-Boltzmann-finite-volume model (LB-FVM) simulations. Micromodel results were directly compared to LB-FVM simulations using two different Pore structures, and excellent agreement was obtained. Six different flow focusing Pore structures were then systematically tested using LB-FVM, and both analytical solutions and a two-dimensional (2D) continuum-Scale model were used to fit α T values to Pore-Scale results. Pore-Scale results indicate that the overall rate of mixing-limited reaction increased by up to 40% when flow focusing occurred, and it was greater in Pore structures with longer flow focusing regions and greater porosity contrast. For each Pore structure, α T values from analytical solutions of transverse concentration profiles or total product at a given longitudinal location showed good agreement for nonreactive and reactive solutes, and values determined in flow focusing zones were always smaller than those downgradient after the flow focusing zone. Transverse dispersivity values from the 2D continuum model were between values within and downgradient from the flow focusing zone determined from analytical solutions. Also, total product and transverse concentration profiles along the entire Pore structure from the 2D continuum model matched Pore Scale results. These results indicate that accurate quantification of Pore-Scale flow focusing with transverse dispersion coefficients is possible only when the entire flow and concentration fields are considered.

  • Pore Scale modeling of dissolution from variably distributed nonaqueous phase liquid blobs
    Water Resources Research, 2001
    Co-Authors: Chad Knutson, Charles J. Werth, Albert J Valocchi
    Abstract:

    Contamination of groundwater by nonaqueous phase liquids (NAPLs) is widely recognized as a serious environmental problem. Predicting the dissolution, fate, and transport of these organic chemicals in the subsurface is challenging because geological heterogeneity exists at numerous Scales. To better understand heterogeneity at the Pore Scale, we use the lattice Boltzmann (LB) method to simulate water flow and solute transport from distributed NAPL blobs in a two-dimensional porous media. The LB method approximates the momentum and mass transport equations at the Pore Scale, easily incorporating complex boundary conditions of the porous media. The effects of NAPL blob configuration and Peclet number (Pe) on steady state mass transfer are studied at 7% and 15% NAPL saturation. We find that the solute flux out of the simulated system decreases substantially as the transverse length over which NAPL blobs are distributed decreases; for example, the solute flux is reduced by a factor of 2 by confining the NAPL blobs to only half of the transverse length. Values of Sherwood numbers determined from our simulations are slightly less than values determined from previously published mass transfer correlations. Our results indicate that Pore-Scale NAPL configuration significantly affects mass transfer and that correlations should be modified to account for it. We find that the dimensionless mass transfer coefficient increases with Pe for the values used in our simulations, where the rate of increase decreases with increasing Pe. We observe that much of the variability in computed mass transfer coefficients is accounted for by differences in the NAPL-water interfacial area at high Pe. However, at lower Pe, variability remains due to NAPL configuration.

Dongxiao Zhang - One of the best experts on this subject based on the ideXlab platform.

  • lattice boltzmann Pore Scale model for multicomponent reactive transport in porous media
    Journal of Geophysical Research, 2006
    Co-Authors: Qinjun Kang, Peter C. Lichtner, Dongxiao Zhang
    Abstract:

    [1] In this work, a multicomponent lattice Boltzmann (LB) model is presented for simulating reactive transport in porous media at the Pore Scale. In the model, a set of distribution functions is introduced to simulate fluid flow and solute transport. The model takes into account advection, diffusion, homogeneous reactions among multiple aqueous species, and heterogeneous reactions between the aqueous solution and minerals, as well as changes in solid and Pore geometry. Homogeneous reactions are described through local equilibrium mass action relations. Mineral reactions are treated kinetically through boundary conditions at the mineral surface. The LB equation for flow recovers the correct Pore-Scale continuity and Navier-Stokes equations. The LB equations for solute transport are modified to recover advection-diffusion equations for total concentrations at the Pore Scale. The model is applied to a hypothetical three-component system with two aqueous complexes and two mineral reactions in a simple Pore geometry. The effects of advection, diffusion, reaction rate constants, equilibrium constants of both homogeneous and heterogeneous reactions, and chemical compositions on mineral alteration of the porous medium and solute concentration are analyzed.

  • Pore Scale study of flow in porous media Scale dependency rev and statistical rev
    Geophysical Research Letters, 2000
    Co-Authors: Dongxiao Zhang, Raoyang Zhang, Shiyi Chen, Wendy E Soll
    Abstract:

    Flow in porous media is studied at the Pore-Scale with lattice Boltzmann simulations on Pore geometries reconstructed from computed microtomographic images. Pore Scale results are analyzed to give quantities such as permeability, porosity and specific surface area at various Scales and at various locations. With this, some fundamental issues such as Scale dependency and medium variability can be assessed quantitatively. More specifically, the existence and size of the well known concept, representative elementary volume (REV), can be quantified. It is found that the size of an REV varies spatially and depends on the quantity being represented. For heterogeneous media, a better measure may be the so called “statistical REV”, which has weaker requirements than does the deterministic REV.