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1
Zimmerman, R. A., G. Severino y D. M. Tartakovsky. "Hydrodynamic dispersion in a tube with diffusive losses through its walls". Journal of Fluid Mechanics 837 (5 de enero de 2018): 546–61. http://dx.doi.org/10.1017/jfm.2017.870.
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Advective–diffusive transport of passive or reactive scalars in confined environments (e.g. tubes and channels) is often accompanied by diffusive losses/gains through the confining walls. We present analytical solutions for transport of a reactive solute in a tube, whose walls are impermeable to flow but allow for solute diffusion into the surrounding medium. The solute undergoes advection, diffusion and first-order chemical reaction inside the tube, while diffusing and being consumed in the surrounding medium. These solutions represent a leading-order (in the radius-to-length ratio) approximation, which neglects the longitudinal variability of solute concentration in the surrounding medium. A numerical solution of the full problem is used to demonstrate the accuracy of this approximation for a physically relevant range of model parameters. Our analysis indicates that the solute delivery rate can be quantified by a dimensionless parameter, the ratio of a solute’s residence time in a tube to the rate of diffusive losses through the tube’s wall.
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Seaïd, Mohammed. "On the Quasi-monotone Modified Method of Characteristics for Transport-diffusion Problems with Reactive Sources". Computational Methods in Applied Mathematics 2, n.º 2 (2001): 186–210. http://dx.doi.org/10.2478/cmam-2002-0012.
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AbstractThis is an attempt to construct a strong numerical method for transportdiffusion equations with nonlinear reaction terms, which relies on the idea of the Modified Method of Characteristics that is explicit but stable and is second-order accurate in time. The method consists in convective-diffusive splitting of the equations along the characteristics. The convective stage of the splitting is straightforwardly treated by a quasi-monotone and conservative modified method of characteristics, while the diffusive-reactive stage can be approximated by an explicit scheme with an extended real stability interval. A numerical comparative study of the new method with Characteristics Crank-Nicholson and Classical Characteristics Runge-Kutta schemes, which are used in many transport-diffusion models, is carried out for several benchmark problems, whose solutions represent relevant transport-diffusion-reaction features. Experiments for transport-diffusion equations with linear and nonlinear reactive sources demonstrate the ability of our new algorithm to better maintain the shape of the solution in the presence of shocks and discontinuities.
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CVETKOVIC, V., J. O. SELROOS y H. CHENG. "Transport of reactive tracers in rock fractures". Journal of Fluid Mechanics 378 (10 de enero de 1999): 335–56. http://dx.doi.org/10.1017/s0022112098003450.
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Transport of tracers subject to mass transfer reactions in single rock fractures is investigated. A Lagrangian probabilistic model is developed where the mass transfer reactions are diffusion into the rock matrix and subsequent sorption in the matrix, and sorption on the fracture surface as well as on gauge (infill) material in the fracture. Sorption reactions are assumed to be linear, and in the general case kinetically controlled. The two main simplifying assumptions are that diffusion in the rock matrix is one-dimensional, perpendicular to the fracture plane, and the tracer is displaced within the fracture plane by advection only. The key feature of the proposed model is that advective transport and diffusive mass transfer are related in a dynamic manner through the flow equation. We have identified two Lagrangian random variables τ and β as key parameters which control advection and diffusive mass transfer, and are determined by the flow field. The probabilistic solution of the transport problem is based on the statistics of (τ, β), which we evaluated analytically using first-order expansions, and numerically using Monte Carlo simulations. To study (τ, β)-statistics, we assumed the ‘cubic law’ to be applicable locally, whereby the pressure field is described with the Reynolds lubrication equation. We found a strong correlation between τ and β which suggests a deterministic relationship β∼τ3/2; the exponent 3/2 is an artifact of the ‘cubic law’. It is shown that flow dynamics in fractures has a strong influence on the variability of τ and β, but a comparatively small impact on the relationship between τ and β. The probability distribution for the (decaying) tracer mass recovery is dispersed in the parameter space due to fracture aperture variability.
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Horsch, Georgios M. "Steady, Diffusive-Reactive Transport in Shallow Triangular Domain". Journal of Engineering Mechanics 124, n.º 10 (octubre de 1998): 1135–41. http://dx.doi.org/10.1061/(asce)0733-9399(1998)124:10(1135).
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Stefanovic, Dragoslav L. y Heinz G. Stefan. "Accurate Two-Dimensional Simulation of Advective-Diffusive-Reactive Transport". Journal of Hydraulic Engineering 127, n.º 9 (septiembre de 2001): 728–37. http://dx.doi.org/10.1061/(asce)0733-9429(2001)127:9(728).
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Heming, T. A., E. K. Stabenau, C. G. Vanoye, H. Moghadasi y A. Bidani. "Roles of intra- and extracellular carbonic anhydrase in alveolar-capillary CO2 equilibration". Journal of Applied Physiology 77, n.º 2 (1 de agosto de 1994): 697–705. http://dx.doi.org/10.1152/jappl.1994.77.2.697.
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Alveolar-capillary CO2 equilibration involves diffusive equilibration of CO2 across the blood-gas barrier and chemical equilibration of perfusate CO2-HCO-3-H+ reactions. These processes are governed by different, but related, driving forces and conductances. The present study examined the importance of pulmonary carbonic anhydrase (CA) for diffusive and reactive CO2 equilibration in isolated rat lungs. Lungs were perfused with salines containing membrane-impermeant or -permeant inhibitors of CA. Measurements of CO2 excretion rate, equilibrated venous and arterial PCO2 and pH, and postcapillary pH and PCO2 disequilibria were used, together with our previous model of CO2-HCO-3-H+ reactions and transport in saline-perfused capillaries (Bidani et al. J. Appl. Physiol. 55: 75–83, 1983), to compute the relevant driving forces and conductances. Reactive CO2 equilibration was markedly affected by extracellular (vascular) CA activity but not by the activity of intracellular (cytosolic) CA. The driving force for CO2 diffusion was strongly influenced by vascular CA activity. The conductance for CO2 diffusion was independent of CA activity. The minimum conductance for CO2 diffusion was estimated to be 700–800 ml.min-1.Torr-1. The results indicate that extracellular vascular CA activity influences both diffusive and reactive CO2 equilibration. However, cytosolic CA has no detectable role in alveolar-capillary CO2 equilibration.
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Liu, Jiangjin, Pablo A. García-Salaberri y Iryna V. Zenyuk. "Bridging Scales to Model Reactive Diffusive Transport in Porous Media". Journal of The Electrochemical Society 167, n.º 1 (2 de enero de 2020): 013524. http://dx.doi.org/10.1149/2.0242001jes.
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Jungnickel, Christian, David Smith y Stephen Fityus. "Coupled multi-ion electrodiffusion analysis for clay soils". Canadian Geotechnical Journal 41, n.º 2 (1 de abril de 2004): 287–98. http://dx.doi.org/10.1139/t03-092.
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For a well-engineered compacted clay landfill liner, diffusive transport through the liner is the main mass transport mechanism from the landfill. Therefore, accurate estimates of diffusion coefficients for clay liners are essential for the engineering design of liner systems. A long-standing problem has been the effect of ion pairing on the estimation of diffusion coefficients for multicomponent ionic solutions migrating through clay liners. This paper considers the solution of a fully coupled set of transport equations describing the simultaneous diffusion of several ion species through a clayey soil. The analysis takes into account the diffusion coefficient for each ion species, ion pairing (as required by electroneutrality of the solution), and time-dependent first-order ion and (or) ligand exchange reactions with the clay particles. The behaviour of a double-reservoir diffusion cell, often employed for the estimation of diffusion coefficients in the laboratory, is analyzed using the coupled transport model. A detailed theoretical analysis is made of sodium fluoride transport through saturated kaolinitic clay.Key words: multi-ion diffusion, finite element analysis, reactive transport, kaolinite, double-reservoir diffusion cell.
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Kapoor, Rajat y S. T. Oyama. "Measurement of solid state diffusion coefficients by a temperature-programmed method". Journal of Materials Research 12, n.º 2 (febrero de 1997): 467–73. http://dx.doi.org/10.1557/jmr.1997.0068.
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This paper presents a method for determining diffusivities in solids where the diffusing species desorbs or reacts at the external surfaces, and where the diffusivity does not vary appreciably with concentration. The method involves measuring the flux of the diffusive species out of the solid under the influence of a temperature program. A general model is developed, based on nonisothermal Fickian diffusion, which is applicable to solid particles with slab or spherical geometry. The solution is presented both as an analytical expression and as correlation charts of experimentally observable quantities. These charts are contour diagrams of the temperatures of peak diffusion rate with ln(E/R) and ln(D0/h2) as the axes, where E and D0 are the activation energy and pre-exponential terms of the diffusivity expression D = D0 exp(−E/RT), where R is the gas constant, and h the size of the particles. This paper deals exclusively with the case of oxygen diffusion in the vanadium oxide system. In this case, vanadium oxide was reduced in a reactive ammonia stream at conditions in which the surface reaction was fast compared to the diffusive transport process. Using this method the diffusion parameters were found to be D0 = 1.9 × 10−5 cm2 s−1 and E = 101 kJ/mol. The method was checked by varying the crystallite size of the vanadium oxide sample in the range 2h = 0.14−0.29 μm.
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Honjo, Yusuke y Thuraisamy Thavaraj. "On uncertainty evaluation of contaminant migration through clayey barriers". Canadian Geotechnical Journal 31, n.º 5 (1 de octubre de 1994): 637–48. http://dx.doi.org/10.1139/t94-076.
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This paper presents a methodology to estimate parameters and to make predictions with quantified uncertainty for an advective–diffusive transport of nonreactive species and low-concentration reactive species through saturated porous media. The methodology is put in the framework of inverse and forward analyses. The maximum-likelihood method (or the weighted least square method) is employed in the inverse analysis, whereas the first-order second-moment method is used in the forward analysis. The methodology facilitates the quantification of uncertainty in the estimated parameters as well as in the predictions. A case study consisting of sets of laboratory tests and field data taken from the literature is used to demonstrate the capability of the proposed methodologies. It is generally recognized that the advective–diffusive transport of contaminants is a rather uncertain process in prediction; therefore the methodology proposed in this study should be useful for practising geotechnical engineers. Key words : statistical analysis, contaminant migration, diffusion, clay barrier, inverse analysis, waste disposal.
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Sevinç Şengör, S., Nicolas F. Spycher, Timothy R. Ginn, Rajesh K. Sani y Brent Peyton. "Biogeochemical reactive–diffusive transport of heavy metals in Lake Coeur d’Alene sediments". Applied Geochemistry 22, n.º 12 (diciembre de 2007): 2569–94. http://dx.doi.org/10.1016/j.apgeochem.2007.06.011.
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Silva, Marcus Vinicius de Assis, Márcio Aredes Martins, Leda Rita D'Antonino Faroni, Jaime Daniel Bustos Vanegas y Adalberto Hipólito de Sousa. "CFD modelling of diffusive-reactive transport of ozone gas in rice grains". Biosystems Engineering 179 (marzo de 2019): 49–58. http://dx.doi.org/10.1016/j.biosystemseng.2018.12.010.
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Kempka, Thomas, Svenja Steding y Michael Kühn. "Verification of TRANSPORT Simulation Environment coupling with PHREEQC for reactive transport modelling". Advances in Geosciences 58 (3 de noviembre de 2022): 19–29. http://dx.doi.org/10.5194/adgeo-58-19-2022.
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Abstract. Many types of geologic subsurface utilisation are associated with fluid and heat flow as well as simultaneously occurring chemical reactions. For that reason, reactive transport models are required to understand and reproduce the governing processes. In this regard, reactive transport codes must be highly flexible to cover a wide range of applications, while being applicable by users without extensive programming skills at the same time. In this context, we present an extension of the Open Source and Open Access TRANSPORT Simulation Environment, which has been coupled with the geochemical reaction module PHREEQC, and thus provides multiple new features that make it applicable to complex reactive transport problems in various geoscientific fields. Code readability is ensured by the applied high-level programming language Python which is relatively easy to learn compared to low-level programming languages such as C, C++ and FORTRAN. Thus, also users with limited software development knowledge can benefit from the presented simulation environment due to the low entry-level programming skill requirements. In the present study, common geochemical benchmarks are used to verify the numerical code implementation. Currently, the coupled simulator can be used to investigate 3D single-phase fluid and heat flow as well as multicomponent solute transport in porous media. In addition to that, a wide range of equilibrium and nonequilibrium reactions can be considered. Chemical feedback on fluid flow is provided by adapting porosity and permeability of the porous media as well as fluid properties. Thereby, users are in full control of the underlying functions in terms of fluid and rock equations of state, coupled geochemical modules used for reactive transport, dynamic boundary conditions and mass balance calculations. Both, the solution of the system of partial differential equations and the PHREEQC module, can be easily parallelised to increase computational efficiency. The benchmarks used in the present study include density-driven flow as well as advective, diffusive and dispersive reactive transport of solutes. Furthermore, porosity and permeability changes caused by kinetically controlled dissolution-precipitation reactions are considered to verify the main features of our reactive transport code. In future, the code implementation can be used to quantify processes encountered in different types of subsurface utilisation, such as water resource management as well as geothermal energy production, as well as geological energy, CO2 and nuclear waste storage.
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Rembert, Flore, Damien Jougnot, Linda Luquot y Roger Guérin. "Interpreting Self-Potential Signal during Reactive Transport: Application to Calcite Dissolution and Precipitation". Water 14, n.º 10 (19 de mayo de 2022): 1632. http://dx.doi.org/10.3390/w14101632.
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Geochemistry and reactive transport play a critical role in many fields. In particular, calcite dissolution and precipitation are chemical processes occurring ubiquitously in the Earth’s subsurface. Therefore, understanding and quantifying them are necessary for various applications (e.g., water resources, reservoirs, geo-engineering). These fundamental geochemical processes can be monitored using the self-potential (SP) method, which is sensitive to pore space changes, water mineralization, and mineral–solution interactions. However, there is a lack of physics-based models linking geochemical processes to the SP response. Thus, in this study, we develop the first geochemical–geophysical fully coupled multi-species numerical workflow to predict the SP electrochemical response. This workflow is based on reactive transport simulation and the computation of a new expression for the electro-diffusive coupling for multiple ionic species. We apply this workflow to calcite dissolution and precipitation experiments, performed for this study and focused on SP monitoring alternating with sample electrical conductivity (EC) measurements. We carried out this experimental part on a column packed with calcite grains, equipped for multichannel SP and EC monitoring and subjected to alternating dissolution or precipitation conditions. From this combined experimental investigation and numerical analysis, the SP method shows clear responses related to ionic concentration gradients, well reproduced with electro-diffusive simulation, and no measurable electrokinetic coupling. This novel coupled approach allows us to determine and predict the location of the reactive zone. The workflow developed for this study opens new perspectives for SP applications to characterize biogeochemical processes in reactive porous media.
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Fernández, Ariel y Oktay Sinanoğlu. "A Reactive System with Diffusive Transport Displaying Two Different Symmetry-Breaking Dissipative Structures". Zeitschrift für Naturforschung A 40, n.º 6 (1 de junio de 1985): 611–18. http://dx.doi.org/10.1515/zna-1985-0612.
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An open reactive system is modelled by coupling the chemical kinetics to diffuse transport. This system operates far from the regime of linear irreversible thermodynamics. The kinetics correspond to a certain region in the parameter space of the Oregonator for which two symmetrybreakdowns occur: a) A periodic orbit contained in an unstable manifold of the phase space. This solution is invariant under time-translations generated by a period. b) A spatial stationary dissipative structure. This solution is invariant under a subgroup of the space symmetry group. The initial time periodicity of the system is followed by a spatial pattern. The restriction to the center manifold in the phase space allows to reduce an infinitedimensional problem for the bifurcation of a semiflow to a finite dimensional system of ordinary differential equations. The ranges in the control concentrations for this dynamics is found in accord with the experimental values. We also demonstrate that if the vessel is stirred after the Turing pattern has emerged, the freezed wave is destroyed and the time-periodic behavior is achieved again.
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Schneider, R., A. Rai, A. Mutzke, M. Warrier, E. Salonen y K. Nordlund. "Dynamic Monte-Carlo modeling of hydrogen isotope reactive–diffusive transport in porous graphite". Journal of Nuclear Materials 367-370 (agosto de 2007): 1238–42. http://dx.doi.org/10.1016/j.jnucmat.2007.03.226.
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Rai, A., M. Warrier y R. Schneider. "A hierarchical multi-scale method to simulate reactive–diffusive transport in porous media". Computational Materials Science 46, n.º 2 (agosto de 2009): 469–78. http://dx.doi.org/10.1016/j.commatsci.2009.03.038.
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Chen, Ping, Luc R. Van Loon, Steffen Koch, Peter Alt-Epping, Tobias Reich y Sergey V. Churakov. "Reactive transport modeling of diffusive mobility and retention of TcO4− in Opalinus Clay". Applied Clay Science 251 (abril de 2024): 107327. http://dx.doi.org/10.1016/j.clay.2024.107327.
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Piazza, Stefania, Mariacrocetta Sambito y Gabriele Freni. "Analysis of Optimal Sensor Placement in Looped Water Distribution Networks Using Different Water Quality Models". Water 15, n.º 3 (31 de enero de 2023): 559. http://dx.doi.org/10.3390/w15030559.
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Urban looped water distribution systems are highly vulnerable to water quality issues. They could be subject to contamination events (accidental or deliberate), compromising the water quality inside them and causing damage to the users’ health. An efficient monitoring system must be developed to prevent this, supported by a suitable model for assessing water quality. Currently, several studies use advective–reactive models to analyse water quality, neglecting diffusive transport, which is claimed to be irrelevant in turbulent flows. Although this may be true in simple systems, such as linear transport pipes, the presence of laminar flows in looped systems may be significant, especially at night and in the peripheral parts of the network. In this paper, a numerical optimisation approach has been compared with the results of an experimental campaign using three different numerical models as inputs (EPANET advective model, the AZRED model in which diffusion–dispersion equations have been implemented, and a new diffusive–dispersive model in dynamic conditions using the random walk method, EPANET-DD). The optimisation problem was formulated using the Monte Carlo method. The results demonstrated a significant difference in sensor placement based on the numerical model.
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Fazeli, Hossein, Ravi Patel y Helge Hellevang. "Effect of Pore-Scale Mineral Spatial Heterogeneity on Chemically Induced Alterations of Fractured Rock: A Lattice Boltzmann Study". Geofluids 2018 (18 de julio de 2018): 1–28. http://dx.doi.org/10.1155/2018/6046182.
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Fractures are the main flow path in rocks with very low permeability, and their hydrodynamic properties might change due to interaction with the pore fluid or injected fluid. Existence of minerals with different reactivities and along with their spatial distribution can affect the fracture geometry evolution and correspondingly its physical and hydrodynamic properties such as porosity and permeability. In this work, evolution of a fracture with two different initial spatial mineral heterogeneities is studied using a pore-scale reactive transport lattice Boltzmann method- (LBM-) based model. The previously developed LBM transport solver coupled with IPHREEQC in open-source Yantra has been extended for simulating advective-diffusive reactive transport. Results show that in case of initially mixed structures for mineral assemblage, a degraded zone will form after dissolution of fast-dissolving minerals which creates a resistance to flow in this region. This causes the permeability-porosity relationship to deviate from a power-law behavior. Results show that permeability will reach a steady-state condition which also depends on transport and reaction conditions. In case of initially banded structures, a comb-tooth zone will form and the same behavior as above is observed; however, in this case, permeability is usually less than that of mixed structures.
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Santschi, Peter H., Urs P. Nyffeler, Robert F. Anderson, Sherry L. Schiff, Patricia O'hara y Raymond H. Hesslein. "Response of Radioactive Trace Metals to Acid–Base Titrations in Controlled Experimental Ecosystems: Evaluation of Transport Parameters for Application to Whole-Lake Radiotracer Experiments". Canadian Journal of Fisheries and Aquatic Sciences 43, n.º 1 (1 de enero de 1986): 60–77. http://dx.doi.org/10.1139/f86-008.
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Radiotracer experiments were carried out in 20 enclosures located in two lakes at the Experimental Lakes Area (ELA), northwestern Ontario, to study pathways of trace metal removal from the water column of shallow lakes. Two removal mechanisms were characterized: (1) sorption to and subsequent transport with falling particles and (2) direct adsorption to surface sediments. Our approach was to measure independently the kinetics of radiotracer sorption, fluxes and concentrations for particles, particle settling velocities, and the "equivalent stagnant boundary film." Our radiotracer results enabled us to test the sensitivity of the tracer removal rates on these rate-determining processes using a numerical transport model. Acid titrations of whole ecosystems revealed that some trace metals (e.g. Mn, Co, and Zn) can diffuse back to the water column as the pH is lowered from 6.5 to 4.8 after 18 d, while others remain tightly bound (e.g. Sn, Fe, Se, Cr, Ag, and Hg isotopes). Subsequent CaCO3 additions to bring back the pH to its original value restored the initial removal conditions for acid-sensitive radiotracers, indicating that the pH sensitivity is reversible. Transport parameters for particle-related pathways or diffusive pathways across the sediment–water interface obtained from our enclosure experiments were used to predict the removal rates of "particle-reactive" 60Co and the "diffusive" pathway tracer 134Cs observed in earlier experiments where radiotracers were added to whole lakes or to larger enclosures.
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Kulenkampff, Johannes, Till Bollermann, Maria A. Cardenas Rivera y Cornelius Fischer. "Transport in tight material enlightened by process tomography". Safety of Nuclear Waste Disposal 1 (10 de noviembre de 2021): 293–94. http://dx.doi.org/10.5194/sand-1-293-2021.
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Abstract. The analysis of fluid transport through tight barrier materials poses two major challenges: (i) Long equilibration periods require long minimum experiment durations, and (ii) the fluid transport frequently results in complex pattern formation. Measuring times that are too short may feign transport rates that are too low; intact homogeneous samples are often missing problematic features, e.g. fractures. Both issues are detected and analyzed by using process tomography techniques, thereby providing an improved understanding of transport processes in complex materials. We thus continuously develop and apply the positron emission tomography (PET) method for geomaterials (Kulenkampff et al., 2016). This is able to trace very low concentrations of β+-emitting radionuclides during their passage through drill cores of barrier material with reasonable resolution (1 mm) and over variable periods (hours to years). The method yields time-resolved quantitative tomographic images of the tracer concentration (e.g. https://doi.org/10.5281/zenodo.166509), in contrast to input-output experiments like common permeability measurements, diffusion cells or break-through curves. Our current research includes the analysis of diffusive transport in heterogeneous shales (sandy facies of the Opalinus Clay) (BMBF and HGF iCross project), the reactive flow in fracture-filling materials of crystalline rocks (Eurad FUTURE project) and transport in engineered barriers and the contact zone (Euratom Cebama, Eurad Magic, as well as MgO and Stroefun BMWi projects). The efforts combine flow field tomography, structural imaging and reactive transport modelling to improve process understanding and to provide a bridge from the molecular to the macroscopic scale. The benefits include: Insight into temporal stability and spatial heterogeneity of the observed transport process Parameterization of local velocity distribution and effective volume as well as comparability with pore-scale model simulations Ability to quantify multiple internal transport rates without the need to register the delayed output signal Transparent and palpable visualization of processes hidden in the opaque material The method requires specific constraints of the experimental setup (size, fluid pressure, temperature). Nevertheless, it provides unique insight into reactive transport processes observed in potential materials for nuclear waste management.
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Våg, Jan E., Hong Wang y Helge K. Dahle. "Eulerian-Lagrangian localized adjoint methods for systems of nonlinear advective-diffusive-reactive transport equations". Advances in Water Resources 19, n.º 5 (octubre de 1996): 297–315. http://dx.doi.org/10.1016/0309-1708(96)00006-1.
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Thomas, Hywel Rhys, Majid Sedighi y Philip James Vardon. "Diffusive Reactive Transport of Multicomponent Chemicals Under Coupled Thermal, Hydraulic, Chemical and Mechanical Conditions". Geotechnical and Geological Engineering 30, n.º 4 (25 de marzo de 2012): 841–57. http://dx.doi.org/10.1007/s10706-012-9502-9.
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Yan, Zhifeng, Xiaofan Yang, Siliang Li y Markus Hilpert. "Two-relaxation-time lattice Boltzmann method and its application to advective-diffusive-reactive transport". Advances in Water Resources 109 (noviembre de 2017): 333–42. http://dx.doi.org/10.1016/j.advwatres.2017.09.003.
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Poonoosamy, Jenna, Renchao Lu, Mara Iris Lönartz, Guido Deissmann, Dirk Bosbach y Yuankai Yang. "A Lab on a Chip Experiment for Upscaling Diffusivity of Evolving Porous Media". Energies 15, n.º 6 (16 de marzo de 2022): 2160. http://dx.doi.org/10.3390/en15062160.
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Reactive transport modelling is a powerful tool to assess subsurface evolution in various energy-related applications. Upscaling, i.e., accounting for pore scale heterogeneities into larger scale analyses, remains one of the biggest challenges of reactive transport modelling. Pore scale simulations capturing the evolutions of the porous media over a wide range of Peclet and Damköhler number in combination with machine learning are foreseen as an efficient methodology for upscaling. However, the accuracy of these pore scale models needs to be tested against experiments. In this work, we developed a lab on a chip experiment with a novel micromodel design combined with operando confocal Raman spectroscopy, to monitor the evolution of porous media undergoing coupled mineral dissolution and precipitation processes due to diffusive reactive fluxes. The 3D-imaging of the porous media combined with pore scale modelling enabled the derivation of upscaled transport parameters. The chemical reaction tested involved the replacement of celestine by strontianite, whereby a net porosity increase is expected because of the smaller molar volume of strontianite. However, under our experimental conditions, the accessible porosity and consequently diffusivity decreased. We propose a transferability of the concepts behind the Verma and Pruess relationship to be applied to also describe changes of diffusivity for evolving porous media. Our results highlight the importance of calibrating pore scale models with quantitative experiments prior to simulations over a wide range of Peclet and Damköhler numbers of which results can be further used for the derivation of upscaled parameters.
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Karimi, S. y K. B. Nakshatrala. "Do Current Lattice Boltzmann Methods for Diffusion and Advection-Diffusion Equations Respect Maximum Principle and the Non-Negative Constraint?" Communications in Computational Physics 20, n.º 2 (21 de julio de 2016): 374–404. http://dx.doi.org/10.4208/cicp.181015.270416a.
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AbstractThe Lattice Boltzmann Method (LBM) has established itself as a popular numerical method in computational fluid dynamics. Several advancements have been recently made in LBM, which include multiple-relaxation-time LBM to simulate anisotropic advection-diffusion processes. Because of the importance of LBM simulations for transport problems in subsurface and reactive flows, one needs to study the accuracy and structure preserving properties of numerical solutions under the LBM. The solutions to advective-diffusive systems are known to satisfy maximum principles, comparison principles, the non-negative constraint, and the decay property. In this paper, using several numerical experiments, it will be shown that current single- and multiple-relaxation-time lattice Boltzmann methods fail to preserve these mathematical properties for transient diffusion-type equations. We will also show that these violations may not be removed by simply refining the discretization parameters. More importantly, it will be shown that meeting stability conditions alone does not guarantee the preservation of the aforementioned mathematical principles and physical constraints in the discrete setting. A discussion on the source of these violations and possible approaches to avoid them is included. A condition to guarantee the non-negativity of concentration under LBM in the case of isotropic diffusion is also derived. The impact of this research is twofold. First, the study poses several outstanding research problems, which should guide researchers to develop LBM-based formulations for transport problems that respect important mathematical properties and physical constraints in the discrete setting. This paper can also serve as a good source of benchmark problems for such future research endeavors. Second, this study cautions the practitioners of the LBM for transport problems with the associated numerical deficiencies of the LBM, and provides guidelines for performing predictive simulations of advective-diffusive processes using the LBM.
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Kortunov, Evgenii, Chuanhe Lu, Richard Amos y Peter Grathwohl. "Redox hydrogeochemistry of organic rich floodplain exemplified by Ammer river". E3S Web of Conferences 98 (2019): 09014. http://dx.doi.org/10.1051/e3sconf/20199809014.
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Diffusive groundwater pollution caused by agricultural and atmospheric inputs is a pressing issue in environmental management worldwide. Various researchers have studied nitrate contamination since the substantial increase of nitrogen fertilization in agriculture starting in the second half of the 20th century. This study addresses large scale reactive solute transport in typical landscapes and aquifers exemplified by geological analogues of southwestern Germany.. Fate of nitrate and other solutes (e.g. agricultural nitrate, ammonium, natural sulfate and dissolved organic carbon) was studied in a typical small river floodplain. Reactive transport model of Ammer river floodplain shows that agriculture nitrate is reduced rapidly in the Ammer floodplain sediments. However, there is a potential for geogenic production of ammonium in sediment layers high in organic carbon and peat, which might be a major source of nitrate in the drains. Part of the nitrate in drains and creeks in the Ammer valley thus could be of geogenic origin. Such findings are relevant for regional land and water quality management.
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Jenni, Andreas y Urs Mäder. "Reactive Transport Simulation of Low-pH Cement Interacting with Opalinus Clay Using a Dual Porosity Electrostatic Model". Minerals 11, n.º 7 (22 de junio de 2021): 664. http://dx.doi.org/10.3390/min11070664.
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Strong chemical gradients between clay and concrete porewater lead to diffusive transport across the interface and subsequent mineral reactions in both materials. These reactions may influence clay properties such as swelling behaviour, permeability or radionuclide retention, which are relevant for the safety of a radioactive waste repository. Different cement types lead to different interactions with Opalinus Clay (OPA), which must be understood to choose the most suitable material. The consideration of anion-depleted porosity due to electrostatic repulsion in clay modelling substantially influences overall diffusive transport and pore clogging at interfaces. The identical dual porosity model approach previously used to predict interaction between Portland cement and OPA is now applied to low-alkali cement—OPA interaction. The predictions are compared with corresponding samples from the cement-clay interaction (CI) experiment in the Mont Terri underground rock laboratory (Switzerland). Predicted decalcification of the cement at the interface (depletion of C–S–H and absence of ettringite within 1 mm from the interface), the Mg enrichment in clay and cement close to the interface (neoformation of up to 17 vol% Mg hydroxides in concrete, and up to 6 vol% in OPA within 0.6 mm at the interface), and the slightly increased S content in the cement 3–4 mm away from the interface qualitatively match the sample characterisation. Simulations of Portland cement—OPA interaction indicate a weaker chemical disturbance over a larger distance compared with low-pH cement—OPA. In the latter case, local changes in porosity are stronger and lead to predicted pore clogging.
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Poonoosamy, Jenna, Martina Klinkenberg, Mara Lönartz, Yuankai Yang, Guido Deissmann, Felix Brandt y Dirk Bosbach. "Combining innovative experimental approaches and cross-scale reactive transport modelling for assessing coupled hydrogeochemical processes at interfaces in deep geological repositories for radioactive waste". Safety of Nuclear Waste Disposal 1 (10 de noviembre de 2021): 105–7. http://dx.doi.org/10.5194/sand-1-105-2021.
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Abstract. Deep geological repositories with a multi-barrier concept are foreseen by various countries for the disposal of high-level radioactive waste. A reliable and consistent assessment of the safety of these repositories over time scales of some hundred thousand years requires an advancement of process understanding. Simulation tools need to be developed for a close-to-reality description of repository evolution scenarios. This is especially required to resolve the challenging task of comparing and assessing the safety of different repository concepts in different host rocks within the German site-selection process. The construction of underground galleries and geotechnical barriers in the host rock formation and the emplacement of nuclear waste packages will create perturbations induced by chemical, thermal and pressure gradients at the interfaces of the different barriers, leading to mineral dissolution and precipitation to achieve re-equilibration. Such coupled hydrogeochemical processes generate non-linear responses in transport and mechanical properties of barrier materials and host rocks, which have to be taken into account for a more rigorous assessment of repository system evolution. Reactive transport modeling (RTM) can be applied to investigate these perturbations and processes across temporal and spatial scales, from the micro-scale at interfaces via the repository near field to the entire repository system – information not accessible through experiments alone. Although RTM is capable of addressing highly complex hydrogeochemical phenomena, the application of RTM codes to real systems is impeded by the often simplified description of coupled processes. To enhance the predictive capabilities of reactive transport models and to gain fundamental insights into the coupling between solute and radionuclide transport properties (e.g., permeability and diffusivity) of porous media and dissolution/precipitation processes, we conducted experiments on “simplified” chemical systems combined with pore-scale and continuum-scale reactive transport modelling to study processes in isolation, with the final aim of improving conceptual approaches for process couplings implemented in reactive transport codes. In this context, we investigated the effects of coupled mineral dissolution and precipitation in porous media on changes in permeability using flow-through experiments conducted in a magnetic resonance imaging scanner, which enabled the in situ investigation of porosity evolution in combination with monitoring changes in permeability and mineralogy. Our observations showed that classical implementations in reactive transport codes such as the Kozeny–Carman equation (Carman, 1937) failed to reproduce the changes in permeability and that more sophisticated approaches are required (Poonoosamy et al., 2020a, b). Moreover, we developed a novel “lab-on-a-chip” setup, i.e., micronized counter diffusion reactors with in operando 3D Raman tomography (Poonoosamy et al., 2019, 2020c), which enables evaluation of the alteration in pore architecture and study of the effect of coupled mineral dissolution and precipitation on the diffusive transport of solutes and radionuclides in porous media. Our approach enables the development of process-based theoretical models which allow for improvements in RTM codes and for predicting the evolution of perturbed interfaces in waste repositories, thus building confidence in the predictive capabilities of reactive transport models and reducing uncertainties with respect to future repository evolution.
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Sangani, Ashok S. "Effective reaction rate on a heterogeneous surface". Journal of Fluid Mechanics 830 (29 de septiembre de 2017): 350–68. http://dx.doi.org/10.1017/jfm.2017.588.
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We examine the problem of prescribing the macroscale boundary condition to the solute convective–diffusive mass transport equation at a heterogeneous surface consisting of reactive circular disks distributed uniformly on a non-reactive surface. The reaction rate at the disks is characterized by a first-order kinetics. This problem was examined by Shah & Shaqfeh (J. Fluid Mech., vol. 782, 2015, pp. 260–299) who obtained the boundary condition in terms of an effective first-order rate constant, which they determined as a function of the Péclet number $Pe=\dot{\unicode[STIX]{x1D6FE}}a^{2}/D$, the fraction $\unicode[STIX]{x1D719}$ of the surface area occupied by the reactive disks and the non-dimensional reaction rate constant $K=ka/D$. Here, $a$ is the radius of the disks, $D$ is the solute diffusivity, $\dot{\unicode[STIX]{x1D6FE}}$ is the wall shear rate and $k$ is the first-order surface-reaction rate constant. Their analysis assumed that $Pe$ and $K$ are $O(1)$ while the ratio of the microscale $a$ to the macroscale $H$ is small. The macroscale transport process is convection–diffusion dominated under these conditions. We examine here the case when the non-dimensional numbers based on the macroscale $H$ are $O(1)$. In this limit the microscale transport problem is reaction rate dominated. We find that the boundary condition can be expressed in terms of an effective rate constant only up to $O(\unicode[STIX]{x1D716})$, where $\unicode[STIX]{x1D716}=a/H$. Higher-order expressions for the mass flux involve both the macroscopic concentration and its surface gradient. The $O(\unicode[STIX]{x1D716})$ microscale problem is relatively easy to solve as the convective effects are unimportant and it is possible to obtain analytical expressions for the effective rate constant as a function of $\unicode[STIX]{x1D719}$ for both periodic and random arrangement of the disks without having to solve the boundary integral equation as was done by Shah and Shaqfeh. The results thus obtained are shown to be in good agreement with those obtained numerically by Shah and Shaqfeh for $Pe=0$. In a separate study, Shah et al. (J. Fluid Mech., vol. 811, 2017, pp. 372–399) examined the inverse-geometry problem in which the disks are inert and the rest of the surface surrounding them is reactive. We show that the two problems are related when $Pe=0$ and $kH/D=O(1)$. Finally, a related problem of determining the current density at a surface consisting of an array of microelectrodes is also examined and the analytical results obtained for the current density are found to agree well with the computed values obtained by solving the integral equation numerically by Lucas et al. (SIAM J. Appl. Maths, vol. 57(6), 1997, pp. 1615–1638) over a wide range of parameters characterizing this problem.
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SCHULZ, RAPHAEL. "Degenerate equations in a diffusion–precipitation model for clogging porous media". European Journal of Applied Mathematics 31, n.º 6 (18 de diciembre de 2019): 1050–69. http://dx.doi.org/10.1017/s0956792519000391.
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In this article, we consider diffusive transport of a reactive substance in a saturated porous medium including variable porosity. Thereby, the evolution of the microstructure is caused by precipitation of the transported substance. We are particularly interested in analysing the model when the equations degenerate due to clogging. Introducing an appropriate weighted function space, we are able to handle the degeneracy and obtain analytical results for the transport equation. Also the decay behaviour of this solution with respect to the porosity is investigated. There a restriction on the decay order is assumed, that is, besides low initial concentration also dense precipitation leads to possible high decay. We obtain nonnegativity and boundedness for the weak solution to the transport equation. Moreover, we study an ordinary differential equation (ODE) describing the change of porosity. Thereby, the control of an appropriate weighted norm of the gradient of the porosity is crucial for the analysis of the transport equation. In order to obtain global in time solutions to the overall coupled system, we apply a fixed point argument. The problem is solved for substantially degenerating hydrodynamic parameters.
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Gahn, Markus y Maria Neuss-Radu. "Singular Limit for Reactive Diffusive Transport Through an Array of Thin Channels in case of Critical Diffusivity". Multiscale Modeling & Simulation 19, n.º 4 (enero de 2021): 1573–600. http://dx.doi.org/10.1137/21m1390505.
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Chapman, Steven, Beth Parker, Tom Al, Richard Wilkin, Diana Cutt, Katherine Mishkin y Shane Nelson. "Field, Laboratory and Modeling Evidence for Strong Attenuation of a Cr(VI) Plume in a Mudstone Aquifer Due to Matrix Diffusion and Reaction Processes". Soil Systems 5, n.º 1 (16 de marzo de 2021): 18. http://dx.doi.org/10.3390/soilsystems5010018.
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This study uses a combination of conventional and high resolution field and laboratory methods to investigate processes causing attenuation of a hexavalent chromium (Cr(VI)) plume in sedimentary bedrock at a former industrial facility. Groundwater plume Cr(VI) concentrations decline by more than three orders of magnitude over a 900 m distance down gradient from the site. Internal plume concentrations generally exhibit stable to declining trends due to diffusive and reactive transport in the low permeability matrix as fluxes from the contamination source dissipate due to natural depletion processes and active remediation efforts. The strong attenuation is attributed to diffusion from mobile groundwater in fractures to immobile porewater in the rock matrix, and reactions causing transformation of aqueous Cr(VI) to low-solubility Cr(III) precipitates, confirmed by high spatial resolution rock matrix contaminant concentrations and comparisons with groundwater concentrations from multi-level sampling within the plume. Field characterization data for the fracture network and matrix properties were used to inform 2-D discrete-fracture matrix (DFM) numerical model simulations that quantify attenuation due to diffusion and reaction processes, which show consistency with field datasets, and provide insights regarding future plume conditions. The combination of field, laboratory and modeling evidence demonstrates effects of matrix diffusion and reaction processes causing strong attenuation of a Cr(VI) plume in a sedimentary bedrock aquifer. This approach has important implications for characterization of sites with Cr(VI) contamination for improved site conceptual models and remediation decision-making.
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Albert, Mary R. "Effects of snow and firn ventilation on sublimation rates". Annals of Glaciology 35 (2002): 52–56. http://dx.doi.org/10.3189/172756402781817194.
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AbstractVapor transport in snow and firn plays a key role in post-depositional changes of many reactive species, in mass and energy balance of large snow-covered areas, and in metamorphic changes of the crystal structure of the snow itself. While conventional estimates of vapor transport and sublimation rate are based on diffusion of water vapor from the snow surface to the atmosphere, ventilation (airflow through interstitial pore spaces) in snow and firn can affect the top several meters of firn, yet the effects of ventilation on sublimation rates in firn have not been previously investigated. In this paper we present the first calculations of sublimation rates due to advective/ diffusive airflow and vapor transport in the snow and firn. Airflow velocities, vapor transport and sublimation rates are calculated using a two-dimensional finite-element model. the airflow patterns induce regions of sublimation and regions of condensation within the snow and firn. Because small surface sastrugi move in time as the snow surface profile changes due to wind redeposition, the subsurface flow and regions of condensation and sublimation will also likely change on a time-scale of days to weeks. However, if the roughness features are such that they move very little over time, it is likely that the regions of condensation and sublimation will have a noticeable effect on the microstructure of the firn. While the highest mass-transfer rates occur near the surface, the depth of vapor transport and phase change depends on firn properties, wavelength of the snow surface roughness, and temperature.
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Warrier, M., A. Rai y R. Schneider. "A time dependent model to study the effect of surface roughness on reactive–diffusive transport in porous media". Journal of Nuclear Materials 390-391 (junio de 2009): 203–6. http://dx.doi.org/10.1016/j.jnucmat.2009.01.168.
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Zhou, Andrew F., Elluz Pacheco, Badi Zhou y Peter X. Feng. "Size-Dependent Electrical Transport Properties in Conducting Diamond Nanostripes". Nanomaterials 11, n.º 7 (6 de julio de 2021): 1765. http://dx.doi.org/10.3390/nano11071765.
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With the advances in nanofabrication technology, horizontally aligned and well-defined nitrogen-doped ultrananocrystalline diamond nanostripes can be fabricated with widths in the order of tens of nanometers. The study of the size-dependent electron transport properties of these nanostructures is crucial to novel electronic and electrochemical applications. In this paper, 100 nm thick n-type ultrananocrystalline diamond thin films were synthesized by microwave plasma-enhanced chemical vapor deposition method with 5% N2 gas in the plasma during the growth process. Then the nanostripes were fabricated using standard electron beam lithography and reactive ion etching techniques. The electrical transport properties of the free-standing single nanostripes of different widths from 75 to 150 nm and lengths from 1 to 128 μm were investigated. The study showed that the electrical resistivity of the n-type ultrananocrystalline diamond nanostripes increased dramatically with the decrease in the nanostripe width. The nanostripe resistivity was nearly doubted when the width was reduced from 150 nm to 75 nm. The size-dependent variability in conductivity could originate from the imposed diffusive scattering of the nanostripe surfaces which had a further compounding effect to reinforce the grain boundary scattering.
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Zhang, Jie, Elisabeth Larsen Kolstad, Wenxin Zhang, Iris Vogeler y Søren O. Petersen. "Modeling coupled nitrification–denitrification in soil with an organic hotspot". Biogeosciences 20, n.º 18 (27 de septiembre de 2023): 3895–917. http://dx.doi.org/10.5194/bg-20-3895-2023.
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Abstract. The emission of nitrous oxide (N2O) from agricultural soils to the atmosphere is a significant contributor to anthropogenic greenhouse gas emissions. The recycling of organic nitrogen (N) in manure and crop residues may result in spatiotemporal variability in N2O production and soil efflux which is difficult to capture by process-based models. We propose a multi-species, reactive transport model to provide detailed insight into the spatiotemporal variability in nitrogen (N) transformations around such N2O hotspots, which consists of kinetic reactions of soil respiration, nitrification, nitrifier denitrification, and denitrification represented by a system of coupled partial differential equations. The model was tested with results from an incubation experiment at two different soil moisture levels (−30 and −100 hPa) and was shown to reproduce the recorded N2O and dinitrogen (N2) emissions and the dynamics of important carbon (C) and N components in soil reasonably well. The simulation indicated that the four different microbial populations developed in closely connected but separate layers, with denitrifying bacteria growing within the manure-dominated zone and nitrifying bacteria in the well-aerated soil outside the manure zone and with time also within the manure layer. The modeled N2O production within the manure zone was greatly enhanced by the combined effect of oxygen deficit, abundant carbon source, and supply of nitrogenous substrates. In the wetter soil treatment with a water potential of −30 hPa, the diffusive flux of nitrate (NO3-) across the manure–soil interface was the main source of NO3- for denitrification in the manure zone, while at a soil water potential of −100 hPa, diffusion became less dominant and overtaken by the co-occurrence of nitrification and denitrification in the manure zone. Scenarios were analyzed where the diffusive transport of dissolved organic carbon or different mineral N species was switched off, and they showed that the simultaneous diffusion of NO3-, ammonium (NH4+), and nitrite (NO2-) was crucial to simulate the dynamics of N transformations and N2O emissions in the model. Without considering solute diffusion in process-based N2O models, the rapid turnover of C and N associated with organic hotspots can not be accounted for, and it may result in the underestimation of N2O emissions from soil after manure application. The model and its parameters allow for new detailed insights into the interactions between transport and microbial transformations associated with N2O emissions in heterogeneous soil environments.
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Dietrich, Joseph P., Frank J. Loge, Timothy R. Ginn y Hakan Başagˇaogˇlu. "Inactivation of particle-associated microorganisms in wastewater disinfection: Modeling of ozone and chlorine reactive diffusive transport in polydispersed suspensions". Water Research 41, n.º 10 (mayo de 2007): 2189–201. http://dx.doi.org/10.1016/j.watres.2007.01.038.
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Anjum, Aisha, Sadaf Masood, Muhammad Farooq, Naila Rafiq y Muhammad Yousaf Malik. "Investigation of binary chemical reaction in magnetohydrodynamic nanofluid flow with double stratification". Advances in Mechanical Engineering 13, n.º 5 (mayo de 2021): 168781402110162. http://dx.doi.org/10.1177/16878140211016264.
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This article addresses MHD nanofluid flow induced by stretched surface. Heat transport features are elaborated by implementing double diffusive stratification. Chemically reactive species is implemented in order to explore the properties of nanofluid through Brownian motion and thermophoresis. Activation energy concept is utilized for nano liquid. Further zero mass flux is assumed at the sheet’s surface for better and high accuracy of the out-turn. Trasnformations are used to reconstruct the partial differential equations into ordinary differential equations. Homotopy analysis method is utilized to obtain the solution. Physical features like flow, heat and mass are elaborated through graphs. Thermal stratified parameter reduces the temperature as well as concentration profile. Also decay in concentration field is noticed for larger reaction rate parameter. Both temperature and concentration grows for Thermophoresis parameter. To check the heat transfer rate, graphical exposition of Nusselt number are also discussed and interpret. It is noticed that amount of heat transfer decreases with the increment in Hartmann number. Numerical results shows that drag force increased for enlarged Hartmann number.
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Dejam, Morteza. "Advective-diffusive-reactive solute transport due to non-Newtonian fluid flows in a fracture surrounded by a tight porous medium". International Journal of Heat and Mass Transfer 128 (enero de 2019): 1307–21. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2018.09.061.
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Chen, Jing, Shuya Li, Ye Zhang, Wei Wang, Xiang Zhang, Yangyang Zhao, Yucai Wang y Hong Bi. "A Reloadable Self-Healing Hydrogel Enabling Diffusive Transport of C-Dots Across Gel-Gel Interface for Scavenging Reactive Oxygen Species". Advanced Healthcare Materials 6, n.º 21 (25 de septiembre de 2017): 1700746. http://dx.doi.org/10.1002/adhm.201700746.
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Begley, S. M. y M. Q. Brewster. "Radiative Properties of MoO3 and Al Nanopowders From Light-Scattering Measurements". Journal of Heat Transfer 129, n.º 5 (28 de junio de 2006): 624–33. http://dx.doi.org/10.1115/1.2712476.
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The combustion behavior of nanometer-scale energetic materials is much different than micron size or larger materials. Burning rates up to 950 m∕s have been reported for a thermite composition of nanosized aluminum and molybdenum trioxide. The energy transport mechanisms in the reactive wave are still uncertain. The relative contribution of radiation has not yet been quantified. To do so analytically requires dependent scattering theory, which has not yet been fully developed. Radiative properties for nanoaluminum and nanomolybdenum-trioxide were obtained experimentally by comparing light scattering measurements on a one-dimensional slab of powder with multiple-scattering simulations using Monte Carlo and discrete ordinate methods. The equivalent isotropic-scattering extinction coefficient for close-packed molybdenum trioxide (MoO3) nanopowder was found to be 5900±450cm−1; the equivalent isotropic-scattering albedo was 0.97±0.035. Aluminum (Al), which proved to be more difficult to work with, had an albedo of 0.35 and 0.38 from two tests. The radiative conductivity based on the MoO3 results is two orders of magnitude less than the diffusive thermal conductivity, indicating that radiation is not a dominant heat transfer mode for the reactive wave propagation of nanothermites under optically thick conditions.
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Barcellos da Rosa, M., W. Behnke y C. Zetzsch. "Study of the heterogeneous reaction of O<sub>3</sub> with CH<sub>3</sub>SCH<sub>3</sub> using the wetted-wall flowtube technique". Atmospheric Chemistry and Physics Discussions 3, n.º 2 (14 de abril de 2003): 1949–71. http://dx.doi.org/10.5194/acpd-3-1949-2003.
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Abstract. This work presents the heterogeneous kinetics of the reaction of CH3SCH3 (dimethyl sulphide, DMS) with O3 (ozone) in aqueous solution at different ionic strengths (0, 0.1 and 1.0 M NaCl) using the wetted-wall flowtube (WWFT) technique. Henry's law coefficients of DMS were determined on pure water and on different concentrations of NaCl (0.1 M–4.0 M) in the WWFT from UV spectrophotometric measurements of DMS in the gas phase using a numerical transport model of phase exchange to be H (M atm−1) = 2.16±0.5 at 274.4 K, 1.47±0.3 at 283.4 K, 0.72±0.2 at 291 K, 0.57±0.1 at 303.4 K and 0.33±0.1 at 313.4K on water, on 1.0M NaCl to be H = 1.57±0.4 at 275.7 K, 0.8±0.2 at 291 K and on 4.0 M NaCl to be H = 0.44±0.1 at 275.7 K and 0.16±0.04 at 29 K, showing a significant effect of ionic strength, mu, on the solubility of DMS according to the equation ln H = −4061 T−1 + 0.052 mu2 + 50.9 μ T−1 + 14.0. At concentrations ofDMS(liq) above 50 μ M, UV spectrophotometry of both O3(gas) and DMS(gas) enables us to observe simultaneously the reactive uptake of O3 on DMS solution and the gas-liquid equilibration of DMS along the flowtube. The uptake coefficient, gamma, of O3 on aqueous solutions of DMS, varying between 1 and 15×10−6, showed a square root-dependence on the aqueous DMS concentration (as expected for diffusive penetration into the surface film, where the reaction takes place in aqueous solution). It was smaller on NaCl solution in accord with the lower solubility of O3. The heterogeneous reaction of O3(gas) with DMS(liq) was evaluated from the observations of the second order rate constant (kII) for the homogeneous aqueous reaction O3(liq) + DMS(liq) using a numerical model of radial diffusion and reactive penetration and leading to kII (in units of 10−8M-1 s-1) = 4.1±1.2 at 291.0 K, 2.15±0.65 at 283.4 K and 1.8±0.5 at 274.4 K. Aside from the expected influence on solubility and aqueous-phase diffusion coefficient of both gases there was no significant effect of ionic strength on kII, that was determined for 0.1M NaCl, leading to kII (108M-1 s-1) = 3.2±1.0 at 288 K, 1.7±0.5 at 282 K and 1.3±0.4 at 276 K, and for 1.0 M NaCl, leading to 3.2±1.0 at 288 K, 1.3±0.4 at 282 K and 1.2±0.4 at 276 K, where the error limits include uncertainties of Henry's law constants and diffusion coefficients for DMS and O3.
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Lehto, Niklas J., William Davison y Hao Zhang. "The use of ultra-thin diffusive gradients in thin-films (DGT) devices for the analysis of trace metal dynamics in soils and sediments: a measurement and modelling approach". Environmental Chemistry 9, n.º 4 (2012): 415. http://dx.doi.org/10.1071/en12036.
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Environmental contextThe recently developed diffusive gradients in thin-films (DGT)-planar optode sandwich probe uses extremely thin resin binding layers, separated from the medium of interest by a very thin material diffusive layer. This work investigates how these changes to the physical nature of a DGT probe are likely to change the interpretation of trace metal measurements in solutions, soils and sediments by using a combination of experimental measurements in well characterised solutions and spiked soils, and advanced reactive transport modelling. AbstractThe interpretation of diffusive gradients in thin-films (DGT) measurements of trace metals in aquatic systems has developed from studies using DGT devices with standard dimensions, but increasingly ultra thin devices are being used for measurements in sediments. This work investigates their performance and the suitability of using traditional data interpretation. The relationship between the concentration of DGT-labile trace metal and the mass of Cu and Cd bound by a 50 µm-thick suspended particulate reagent–imidodiacetate resin binding layer was found to be linear when the total mass of the metals bound by the resin was less than 3 µg cm–2, demonstrating that the capacity is adequate for measurements in uncontaminated environments. An ultra thin DGT probe using a 50 µm-thick resin gel and a 0.01 mm-thick material diffusion layer (MDL), was deployed in soil to demonstrate the spatial resolution in trace metal measurements that can be achieved using this approach. DGT probes with extremely thin (0.01 mm) and more conventional MDLs (0.8 mm) were used to investigate if the mechanisms traditionally used to describe DGT uptake of Cu and Cd from solutions and soil porewaters apply for ultra-thin probes. Interpretation of the results using a dynamic numerical model demonstrated that the processes determining the supply of Cu and Cd to a DGT probe in these media are unlikely to differ for conventional and ultra thin probes, despite the higher metal fluxes to the latter probes. Overall, the results establish that measurements made using ultra-thin DGT devices in soils and sediments can be meaningfully interpreted using an extension of the existing theory.
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Romero, R. y C. Ramis. "A numerical study of the transport and diffusion of coastal pollutants during the breeze cycle in the Island of Mallorca". Annales Geophysicae 14, n.º 3 (31 de marzo de 1996): 351–63. http://dx.doi.org/10.1007/s00585-996-0351-9.
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Abstract. An Eulerian study of the distribution over the Island of Mallorca of a non-reactive pollutant (SO2) emitted from an electric power plant operating at present on the north coast is performed using a meso-β numerical model, paying particular attention to the diffusive physical mechanisms. The study is applied to the conditions of sea-land breeze development. This is a local circulation that dominates the flow during the summer and favours transporting pollutants from the coast toward the centre of the island. Results indicate that values of the ground-level concentration higher than 5 μ g/m3 are restricted over a limited and mountainous region during the whole diurnal cycle. However, when the simulation is carried out with the inclusion of a twin electric plant which may be built on the south coast, the affected area becomes larger, especially early in the morning, when air over the island is sinking as a consequence of the land breeze development. The inclusion of dry deposition in the simulations does not produce important changes in the spatial and temporal evolution of the ground-level concentration.
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Shi, Wenguang, Quanrong Wang, Hongbin Zhan, Renjie Zhou y Haitao Yan. "A general model of radial dispersion with wellbore mixing and skin effects". Hydrology and Earth System Sciences 27, n.º 9 (15 de mayo de 2023): 1891–908. http://dx.doi.org/10.5194/hess-27-1891-2023.
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Abstract. The mechanism of radial dispersion is essential for understanding reactive transport in the subsurface and for estimating the aquifer parameters required in the optimization design of remediation strategies. Many previous studies demonstrated that the injected solute firstly experienced a mixing process in the injection wellbore, then entered a skin zone after leaving the injection wellbore, and finally moved into the aquifer through advective, diffusive, dispersive, and chemical–biological–radiological processes. In this study, a physically based new model and the associated analytical solutions in the Laplace domain are developed by considering the mixing effect, skin effect, scale effect, aquitard effect, and media heterogeneity (in which the solute transport is described in a mobile–immobile framework). This new model is tested against a finite-element numerical model and experimental data. The results demonstrate that the new model performs better than previous models of radial dispersion in interpreting the experimental data. To prioritize the influences of different parameters on the breakthrough curves, a sensitivity analysis is conducted. The results show that the model is sensitive to the mobile porosity and wellbore volume, and the sensitivity coefficient of the wellbore volume increases with the well radius, while it decreases with increasing distance from the wellbore. The new model represents the most recent advancement in radial dispersion study, incorporating many essential processes not considered in previous investigations.
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Larsbo, M., J. Koestel y N. Jarvis. "Controls of macropore network characteristics on preferential solute transport". Hydrology and Earth System Sciences Discussions 11, n.º 8 (12 de agosto de 2014): 9551–88. http://dx.doi.org/10.5194/hessd-11-9551-2014.
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Abstract. In this study we examined the relationships between macropore network characteristics, hydraulic properties and state variables and measures of preferential transport in undisturbed columns sampled from four agricultural topsoils of contrasting texture and structure. Macropore network characteristics were computed from 3-dimensional X-ray tomography images of the soil pore system. Non-reactive solute transport experiments were carried out at five steady-state water flow rates from 2 to 12 mm h−1. The degree of preferential transport was evaluated by the normalised 5% solute arrival time and the apparent dispersivity calculated from the resulting breakthrough curves. Near-saturated hydraulic conductivities were measured on the same samples using a tension disk infiltrometer placed on top of the columns. Results showed that many of the macropore network characteristics were inter-correlated. For example, large macroporosities were associated with larger specific macropore surface areas and better local connectivity of the macropore network. Generally, an increased flow rate resulted in earlier solute breakthrough and a shifting of the peak concentration towards smaller drained volumes. Columns with smaller macroporosities, poorer local connectivity of the macropore network and smaller near-saturated hydraulic conductivities exhibited a greater degree of preferential transport. This can be explained by the fact that, with only two exceptions, global (i.e. sample-scale) continuity of the macropore network was still preserved at low macroporosities. Thus, for any given flow rate pores of larger diameter were actively conducting solute in soils of smaller near-saturated hydraulic conductivity. With less time for equilibration between the macropores and the surrounding matrix the transport became more preferential. Conversely, the large specific macropore surface area and well-connected macropore networks associated with columns with large macroporosities limit the degree of preferential transport because they increase the diffusive flux between macropores and the soil matrix and they increase the near-saturated hydraulic conductivity. The normalised 5% arrival times were most strongly related with the estimated hydraulic state variables (e.g. with the degree of saturation in the macropores R2 = 0.589), since these combine into one measure the effects of irrigation rate and the near-saturated hydraulic conductivity function, which in turn implicitly depends on the volume, size distribution, global continuity, local connectivity and tortuosity of the macropore network.
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Barcellos da Rosa, M., W. Behnke y C. Zetzsch. "Study of the heterogeneous reaction of O<sub>3</sub> with CH<sub>3</sub>SCH<sub>3</sub> using the wetted-wall flowtube technique". Atmospheric Chemistry and Physics 3, n.º 5 (10 de octubre de 2003): 1665–73. http://dx.doi.org/10.5194/acp-3-1665-2003.
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Abstract. This work presents the heterogeneous kinetics of the reaction of CH3SCH3 (dimethyl sulphide, DMS) with O3 (ozone) in aqueous solutions of different ionic strengths (0, 0.1 and 1.0M NaCl) using the wetted-wall flowtube (WWFT) technique. Henry's law coefficients of DMS on pure water and on different concentrations of NaCl (0.1M - 4.0M) in the WWFT from UV spectrophotometric measurements of DMS in the gas phase, using a numerical transport model of phase exchange, were determined to be H ±s (M atm-1) = 2.16±0.5 at 274.4 K, 1.47±0.3 at 283.4 K, 0.72±0.2 at 291 K, 0.57±0.1 at 303.4 K and 0.33±0.1 at 313.4 K on water, on 1.0M NaCl to be H = 1.57±0.4 at 275.7 K, 0.8±0.2 at 291 K and on 4.0M NaCl to be H = 0.44±0.1 at 275.7 K and 0.16±0.04 at 291 K, showing a significant effect of ionic strength, m, on the solubility of DMS according to the equation ln (H/M atm-1) = 4061 T-1 - 0.052 m2 - 50.9 m T-1 - 14.0. At concentrations of DMS(liq) above 50 mM, UV spectrophotometry of both O3(gas) and DMS(gas) enables us to observe simultaneously the reactive uptake of O3 on DMS solution and the gas-liquid equilibration of DMS along the WWFT. The uptake coefficient, g (gamma), of O3 on aqueous solutions of DMS, varying between 1 and 15·10-6, showed a square root-dependence on the aqueous DMS concentration (as expected for diffusive penetration into the surface film, where the reaction takes place in aqueous solution). The uptake coefficient was smaller on NaCl solution in accord with the lower solubility of O3. The heterogeneous reaction of O3(gas) with DMS(liq) was evaluated from the observations of the second order rate constant (kII) for the homogeneous aqueous reaction O3(liq) + DMS(liq) using a numerical model of radial diffusion and reactive penetration, leading to kII ± D kII (in units of 108 M-1 s-1) = 4.1±1.2 at 291.0 K, 2.15±0.65 at 283.4 K and 1.8±0.5 at 274.4 K. Aside from the expected influence on solubility and aqueous-phase diffusion coefficient of both gases there was no significant effect of ionic strength on kII, that was determined for 0.1M NaCl, leading to kII ± D kII (108 M-1 s-1) = 3.2±1.0 at 288 K, 1.7±0.5 at 282 K and 1.3±0.4 at 276 K, and for 1.0M NaCl, leading to 3.2±1.0 at 288 K, 1.3±0.4 at 282 K and 1.2±0.4 at 276 K, where the error limits are estimated from the output of the model calculations, taking the variability of individual runs at various DMS levels into account.
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Daunys, Forster, Schiedek, Olenin y Zettler. "Effect of Species Invasion on Transport of Solutes at Different Levels of Soft Sediment Macrofauna Diversity: Results from an Experimental Approach". Water 11, n.º 8 (25 de julio de 2019): 1544. http://dx.doi.org/10.3390/w11081544.
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Different irrigation or ventilation strategies by macrofauna may provide a competitive advantage to tolerant species invading impacted benthic systems and alter benthic-pelagic coupling. To comparatively analyze the effects of an exotic and a native polychaete burrower on sediment-water exchanges, two laboratory experiments were performed. In the first experiment, the invasive spionid polychaete Marenzelleria neglecta was added to defaunated sediments and fluxes of the inert tracer (bromide, Br−) were measured to quantify the effects of irrigation by the worm on the tracer transport. In the second experiment, M. neglecta or the native polychaete Hediste diversicolor were introduced to a relatively diverse Baltic soft-bottom macrofauna community. The effect of species on fluxes of reactive solutes (ammonium, NH4+, and phosphate, PO43−) and transport rates of Br− was estimated. The results indicate different invasion effects depending on the characteristics of the recipient habitat. In defaunated sediments, a single specimen of M. neglecta significantly enhanced originally low solute exchange rates. Total tracer flux was significantly enhanced over diffusive flux by a factor of 1.6 ± 0.14 (n = 3). In natural sediments, on the other hand, the addition of either M. neglecta or H. diversicolor had no statistically significant effects on benthic fluxes. Tracer flux estimates between control and treatment incubations differed by less than 10% on average, and both reactive solutes tended to increase by 10 to 40% after additions. One specimen of M. neglecta in cores with defaunated sediment generated approximately 20% of the tracer flux produced by the relatively diverse macrofauna community. Estimated net tracer fluxes in two experiments corresponded well with the number of adult polychaetes found in sediments (r2 = 0.73, p = 0.005, n = 12). The invasive M. neglecta produced a small effect on fluxes in biodiverse sediments, comparable to those of H. diversicolor, but it may deeply alter porewater chemistry in azoic sediment. As M. neglecta tolerates chemically reduced and sulphidic conditions, its bioirigation may favor sediment reoxidation and ultimately the recolonization by less tolerant, native species.