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Sample records for chemically heterogeneous porous

  1. Mass transfer in porous media with heterogeneous chemical reaction

    Directory of Open Access Journals (Sweden)

    Souza S.M.A.G.Ulson de

    2003-01-01

    Full Text Available In this paper, the modeling of the mass transfer process in packed-bed reactors is presented and takes into account dispersion in the main fluid phase, internal diffusion of the reactant in the pores of the catalyst, and surface reaction inside the catalyst. The method of volume averaging is applied to obtain the governing equation for use on a small scale. The local mass equilibrium is assumed for obtaining the one-equation model for use on a large scale. The closure problems are developed subject to the length-scale constraints and the model of a spatially periodic porous medium. The expressions for effective diffusivity, hydrodynamic dispersion, total dispersion and the Darcy's law permeability tensors are presented. Solution of the set of final equations permits the variations of velocity and concentration of the chemical species along the packed-bed reactors to be obtained.

  2. A Theoretical Analysis of Colloid Attachment and Straining in Chemically Heterogeneous Porous Media

    DEFF Research Database (Denmark)

    Bradford, Scott A.; Torkzaban, Saeed; Shapiro, Alexander

    2013-01-01

    attachment conditions. This model considers resistance due to deformation and the horizontal component of the adhesive force (FAT), spatial variations in the pore scale velocity distribution, and the influence of hr on lever arms for TH and TA. Values of Sf* were calculated for a wide range of......A balance of applied hydrodynamic (TH) and resisting adhesive (TA) torques was conducted over a chemically heterogeneous porous medium that contained random roughness of height hr to determine the fraction of the solid surface area that contributes to colloid immobilization (Sf*) under unfavorable...... more important for higher IS and variance in the secondary minimum, and for smaller rc, q, and K, but diffusion decreased these values. Conversely, straining was dominant for the opposite conditions. Discrepancies in the literature on mechanisms of colloid retention are likely due to a lack of...

  3. Reactive solute transport in physically and chemically heterogeneous porous media with multimodal reactive mineral facies: the Lagrangian approach.

    Science.gov (United States)

    Soltanian, Mohamad Reza; Ritzi, Robert W; Dai, Zhenxue; Huang, Chao Cheng

    2015-03-01

    Physical and chemical heterogeneities have a large impact on reactive transport in porous media. Examples of heterogeneous attributes affecting reactive mass transport are the hydraulic conductivity (K), and the equilibrium sorption distribution coefficient (Kd). This paper uses the Deng et al. (2013) conceptual model for multimodal reactive mineral facies and a Lagrangian-based stochastic theory in order to analyze the reactive solute dispersion in three-dimensional anisotropic heterogeneous porous media with hierarchical organization of reactive minerals. An example based on real field data is used to illustrate the time evolution trends of reactive solute dispersion. The results show that the correlation between the hydraulic conductivity and the equilibrium sorption distribution coefficient does have a significant effect on reactive solute dispersion. The anisotropy ratio does not have a significant effect on reactive solute dispersion. Furthermore, through a sensitivity analysis we investigate the impact of changing the mean, variance, and integral scale of K and Kd on reactive solute dispersion. PMID:25532767

  4. Reactive solute transport in physically and chemically heterogeneous porous media with multimodal reactive mineral facies: The Lagrangian approach

    CERN Document Server

    Soltanian, Mohamad Reza; Dai, Zhenxue; Huang, Chaocheng

    2014-01-01

    Physical and chemical heterogeneities have a large impact on reactive transport in porous media. Examples of heterogeneous attributes affecting reactive mass transport are the hydraulic conductivity (K), and the equilibrium sorption distribution coefficient (Kd). This paper uses the Deng et al. (2013) conceptual model for multimodal reactive mineral facies and a Lagrangian-based stochastic theory in order to analyze the reactive solute dispersion in three-dimensional anisotropic heterogeneous porous media with hierarchical organization of reactive minerals. An example based on real field data is used to illustrate the time evolution trends of reactive solute dispersion. The results show that the correlation between the hydraulic conductivity and the equilibrium sorption distribution coefficient does have a significant effect on reactive solute dispersion. The anisotropy ratio does not have a significant effect on reactive solute dispersion. Furthermore, through a sensitivity analysis we investigate the impact...

  5. Effective reactive surface area: An anisotropic property of physically and chemically heterogeneous porous media

    International Nuclear Information System (INIS)

    Although transport calculations are often formulated in terms of mass-based isotropic distribution coefficients, it is the abundance of reactive surface areas of subsurface materials that controls contaminant adsorption. In water-saturated homogeneous systems devoid of advective fluxes (e.g., batch experiments), the available reactive surface area is similar to the total surface area (as measured by conventional methods such as BET gas adsorption). However, in physically and chemically heterogeneous systems with advective fluxes, the effective reactive surface area (i.e., the surface area that a packet of advecting water interacts with) is smaller than the laboratory measured surface area and is a complex function of advective velocity and the correlation structures of the physical and chemical heterogeneities. Theoretical derivations for an important but simple type of heterogeneity (fine-scale horizontal layering) suggest that the effective reactive surface area is an anisotropic property of the medium and is inversely correlated with the anisotropy in hydraulic conductivity. The implications of reactive transport anisotropy include the concept that the retardation factor should be treated as a directional property rather than being treated as a constant. Furthermore, because of the inverse relationship between effective reactive surface area and hydraulic conductivity, batch adsorption experiments tend to overestimate the retention of contaminants relative to intact natural materials

  6. Progress on Porous Ceramic Membrane Reactors for Heterogeneous Catalysis over Ultrafine and Nano-sized Catalysts

    Institute of Scientific and Technical Information of China (English)

    JIANG Hong; MENG Lie; CHEN Rizhi; JIN Wanqin; XING Weihong; XU Nanping

    2013-01-01

    Heterogeneous catalysts with ultrafine or nano particle size have currently attracted considerable attentions in the chemical and petrochemical production processes,but their large-scale applications remain challenging because of difficulties associated with their efficient separation from the reaction slurry.A porous ceramic membrane reactor has emerged as a promising method to solve the problem concerning catalysts separation in situ from the reaction mixture and make the production process continuous in heterogeneous catalysis.This article presents a review of the present progress on porous ceramic membrane reactors for heterogeneous catalysis,which covers classification of configurations of porous ceramic membrane reactor,major considerations and some important industrial applications.A special emphasis is paid to major considerations in term of application-oriented ceramic membrane design,optimization of ceramic membrane reactor performance and membrane fouling mechanism.Finally,brief concluding remarks on porous ceramic membrane reactors are given and possible future research interests are also outlined.

  7. Transport of reactive solutes in heterogeneous porous formation.

    NARCIS (Netherlands)

    Bosma, W.J.P.

    1994-01-01

    Transport and spreading behaviour of reactive solutes in heterogeneous porous formations is considered. Spatial variability is modeled by assuming a random space function (RSF) for the spatially variable properties. In the available literature, the effect of random spatial variability is mostly limi

  8. Modeling heterogeneous unsaturated porous media flow at Yucca Mountain

    International Nuclear Information System (INIS)

    Geologic systems are inherently heterogeneous and this heterogeneity can have a significant impact on unsaturated flow through porous media. Most previous efforts to model groundwater flow through Yucca Mountain have used stratigraphic units with homogeneous properties. However, modeling heterogeneous porous and fractured tuff in a more realistic manner requires numerical methods for generating heterogeneous simulations of the media, scaling of material properties from core scale to computational scale, and flow modeling that allows channeling. The Yucca Mountain test case of the INTRAVAL project is used to test the numerical approaches. Geostatistics is used to generate more realistic representations of the stratigraphic units and heterogeneity within units is generated using sampling from property distributions. Scaling problems are reduced using an adaptive grid that minimizes heterogeneity within each flow element. A flow code based on the dual mixed-finite-element method that allows for heterogeneity and channeling is employed. In the Yucca Mountain test case, the simulated volumetric water contents matched the measured values at drill hole USW UZ-16 except in the nonwelded portion of Prow Pass

  9. Modeling heterogeneous unsaturated porous media flow at Yucca Mountain

    International Nuclear Information System (INIS)

    Geologic systems are inherently heterogeneous and this heterogeneity can have a significant impact on unsaturated flow through porous media. Most previous efforts to model groundwater flow through Yucca Mountain have used stratigraphic units with homogeneous properties. However, modeling heterogeneous porous and fractured tuff in a more realistic manner requires numerical methods for generating heterogeneous simulations of the media, scaling of material properties from core scale to computational scale, and flow modeling that allows channeling. The Yucca Mountain test case of the INTRAVAL project is used to test the numerical approaches. Geostatistical methods are used to generate more realistic representations of the stratigraphic units and heterogeneity within units is generated using sampling from property distributions. Scaling problems are reduced using an adaptive grid that minimizes heterogeneity within each flow element. A flow code based on the dual mixed-finite-element method that allows for heterogeneity and channeling is employed. In the Yucca Mountain test case, the simulated volumetric water contents matched the measured values at drill hole USW UZ-16 except in the nonwelded portion of Prow Pass

  10. RECENT ADVANCES OF UPSCALING METHODS FOR THE SIMULATION OF FLOW TRANSPORT THROUGH HETEROGENEOUS POROUS MEDIA

    Institute of Scientific and Technical Information of China (English)

    Zhiming Chen

    2006-01-01

    We review some of our recent efforts in developing upscaling methods for simulating the flow transport through heterogeneous porous media. In particular, the steady flow transport through highly heterogeneous porous media driven by extraction wells and the flow transport through unsaturated porous media will be considered.

  11. Flows and chemical reactions in heterogeneous mixtures

    CERN Document Server

    Prud'homme, Roger

    2014-01-01

    This book - a sequel of previous publications 'Flows and Chemical Reactions' and 'Chemical Reactions in Flows and Homogeneous Mixtures' - is devoted to flows with chemical reactions in heterogeneous environments.  Heterogeneous media in this volume include interfaces and lines. They may be the site of radiation. Each type of flow is the subject of a chapter in this volume. We consider first, in Chapter 1, the question of the generation of environments biphasic individuals: dusty gas, mist, bubble flow.  Chapter 2 is devoted to the study at the mesoscopic scale: particle-fluid exchange of mom

  12. Porous-Hybrid Polymers as Platforms for Heterogeneous Photochemical Catalysis

    KAUST Repository

    Haikal, Rana R.

    2016-07-18

    A number of permanently porous polymers containing Ru(bpy)n photosensitizer or a cobaloxime complex, as a proton-reduction catalyst, were constructed via one-pot Sonogashira-Hagihara (SH) cross-coupling reactions. This process required minimal workup to access porous platforms with control over the apparent surface area, pore volume, and chemical functionality from suitable molecular building blocks (MBBs) containing the Ru or Co complexes, as rigid and multi-topic nodes. The cobaloxime molecular building block, generated through in situ metalation, afforded a microporous solid that demonstrated noticeable catalytic activity towards hydrogen-evolution reaction (HER) with remarkable recyclability. We further demonstrated, in two cases, the ability to affect the excited state lifetime of the covalently-immobilized Ru(bpy)3 complex attained through deliberate utilization of the organic linkers of variable dimensions. Overall, this approach facilitates construction of tunable porous solids, with hybrid composition and pronounced chemical and physical stability, based on the well-known Ru(bpy)nor the cobaloxime complexes.

  13. Heterogeneous electrocatalysis in porous cathodes of solid oxide fuel cells

    CERN Document Server

    Fu, Y; Bertei, A; Qi, C; Mohanram, A; Pietras, J D; Bazant, M Z

    2014-01-01

    A general physics-based model is developed for heterogeneous electrocatalysis in porous electrodes and used to predict and interpret the impedance of solid oxide fuel cells. This model describes the coupled processes of oxygen gas dissociative adsorption and surface diffusion of the oxygen intermediate to the triple phase boundary, where charge transfer occurs. The model accurately captures the Gerischer-like frequency dependence and the oxygen partial pressure dependence of the impedance of symmetric cathode cells. Digital image analysis of the microstructure of the cathode functional layer in four different cells directly confirms the predicted connection between geometrical properties and the impedance response. As in classical catalysis, the electrocatalytic activity is controlled by an effective Thiele modulus, which is the ratio of the surface diffusion length (mean distance from an adsorption site to the triple phase boundary) to the surface boundary layer length (square root of surface diffusivity div...

  14. Nonlocal reactive transport with physical, chemical, and biological heterogeneity

    Science.gov (United States)

    Hu, Bill X.; Cushman, John H.; Deng, Fei-Wen

    When a natural porous medium is viewed from an eulerian perspective, incomplete characterization of the hydraulic conductivity, chemical reactivity, and biological activity leads to nonlocal constitutive theories, irrespective of whether the medium has evolving heterogeneity with fluctuations over all scales. Within this framework a constitutive theory involving nonlocal dispersive and convective fluxes and nonlocal sources/sinks is developed for chemicals undergoing random linear nonequilibrium reactions and random equilibrium first-order decay in a random conductivity field. The resulting transport equations are solved exactly in Fourier-Laplace space and then numerically inverted to real space. Mean concentration contours and various spatial moments are presented graphically for several covariance structures. 1997 Published by Elsevier Science Ltd. All rights reserved

  15. Flow of miscible and immiscible hydrocarbons in heterogeneous porous media

    Energy Technology Data Exchange (ETDEWEB)

    Butts, M.B.

    1996-12-31

    A series of large-scale two-dimensional physical model studies has been carried out in order to better understand and predict the multiphase flow of hydrocarbon contaminants and the release of the water-soluble fraction of such contaminants into the groundwater stream. The detailed measurements of the fluid saturations within the bulk hydrocarbon plume as well as the aqueous concentrations recorded downstream should provide a useful data set for testing and improving numerical models of both multiphase flow and transport. Predictions of a numerical model of immiscible multiphase flow developed in the petroleum industry were found to compare favourably with the observed oil plume for the case of an immiscible oil spill. Nevertheless, subtle layering within the experimental flume altered the long-term development of the oil plume in a manner not predicted by the numerical model. A stochastic model for three-dimensional, two-phase incompressible flow in heterogeneous soil and rock formations is developed. Analytical solutions for the resulting stochastic differential equations are derived for asymptotic flows using a perturbation approach. These solutions were used to derive general expressions for the large-scale (effective) properties for large-scale two-phase flow in porous media. An important observation from this analysis is that general large-scale flow in heterogeneous soils cannot be predicted on the basis of simple averages of the soil hydraulic properties alone. The large-scale capillary pressure saturation relation is evaluated for imbibition into a wet soil or rock formation. (EG) 194 refs.

  16. Complexity Reduction of Multiphase Flows in Heterogeneous Porous Media

    KAUST Repository

    Ghommem, Mehdi

    2015-04-22

    In this paper, we apply mode decomposition and interpolatory projection methods to speed up simulations of two-phase flows in heterogeneous porous media. We propose intrusive and nonintrusive model-reduction approaches that enable a significant reduction in the size of the subsurface flow problem while capturing the behavior of the fully resolved solutions. In one approach, we use the dynamic mode decomposition. This approach does not require any modification of the reservoir simulation code but rather post-processes a set of global snapshots to identify the dynamically relevant structures associated with the flow behavior. In the second approach, we project the governing equations of the velocity and the pressure fields on the subspace spanned by their proper-orthogonal-decomposition modes. Furthermore, we use the discrete empirical interpolation method to approximate the mobility-related term in the global-system assembly and then reduce the online computational cost and make it independent of the fine grid. To show the effectiveness and usefulness of the aforementioned approaches, we consider the SPE-10 benchmark permeability field, and present a numerical example in two-phase flow. One can efficiently use the proposed model-reduction methods in the context of uncertainty quantification and production optimization.

  17. Pore scale heterogeneity in the mineral distribution and surface area of porous rocks

    Science.gov (United States)

    Lai, Peter; Moulton, Kevin; Krevor, Samuel

    2014-05-01

    There are long-standing challenges in characterizing reactive transport in porous media at scales larger than individual pores. This hampers the prediction of the field-scale impact of geochemical processes on fluid flow [1]. This is a source of uncertainty for carbon dioxide injection, which results in a reactive fluid-rock system, particularly in carbonate rock reservoirs. A potential cause is the inability of the continuum approach to incorporate the impact of heterogeneity in pore-scale reaction rates. This results in part from pore-scale heterogeneities in surface area of reactive minerals [2,3]. The objective of this study was to quantify heterogeneity in reactive surface and observe the extent of its non-normal character. In this study we describe our work in using micron-scale x-ray imaging and other spectroscopic techniques for the purpose of describing the statistical distribution of reactive surface area within a porous medium, and identifying specific mineral phases and their distribution in 3-dimensions. Using in-house image processing techniques and auxilary charactersation with thin section, electron microscope and spectroscopic techniques we quantified the surface area of each mineral phase in the x-ray CT images. This quantification was validated against nitrogen BET surface area and backscattered electron imaging measurements of the CT-imaged samples. Distributions in reactive surface area for each mineral phase were constructed by calculating surface areas in thousands of randomly selected subvolume images of the total sample, each normalized to the pore volume in that image. In all samples, there is little correlation between the reactive surface area fraction and the volumetric fraction of a mineral in a bulk rock. Berea sandstone was far less heterogeneous and has a characteristic pore size at which a surface area distribution may be used to quantify heterogeneity. In carbonates, heterogeneity is more complex and surface area must be

  18. On the validity of effective formulations for transport through heterogeneous porous media

    Science.gov (United States)

    de Dreuzy, Jean-Raynald; Carrera, Jesus

    2016-04-01

    Geological heterogeneity enhances spreading of solutes and causes transport to be anomalous (i.e., non-Fickian), with much less mixing than suggested by dispersion. This implies that modeling transport requires adopting either stochastic approaches that model heterogeneity explicitly or effective transport formulations that acknowledge the effects of heterogeneity. A number of such formulations have been developed and tested as upscaled representations of enhanced spreading. However, their ability to represent mixing has not been formally tested, which is required for proper reproduction of chemical reactions and which motivates our work. We propose that, for an effective transport formulation to be considered a valid representation of transport through heterogeneous porous media (HPM), it should honor mean advection, mixing and spreading. It should also be flexible enough to be applicable to real problems. We test the capacity of the multi-rate mass transfer (MRMT) model to reproduce mixing observed in HPM, as represented by the classical multi-Gaussian log-permeability field with a Gaussian correlation pattern. Non-dispersive mixing comes from heterogeneity structures in the concentration fields that are not captured by macrodispersion. These fine structures limit mixing initially, but eventually enhance it. Numerical results show that, relative to HPM, MRMT models display a much stronger memory of initial conditions on mixing than on dispersion because of the sensitivity of the mixing state to the actual values of concentration. Because MRMT does not restitute the local concentration structures, it induces smaller non-dispersive mixing than HPM. However long-lived trapping in the immobile zones may sustain the deviation from dispersive mixing over much longer times. While spreading can be well captured by MRMT models, in general non-dispersive mixing cannot.

  19. On the validity of effective formulations for transport through heterogeneous porous media

    Directory of Open Access Journals (Sweden)

    J.-R. de Dreuzy

    2015-11-01

    Full Text Available Geological heterogeneity enhances spreading of solutes, and causes transport to be anomalous (i.e., non-Fickian, with much less mixing than suggested by dispersion. This implies that modeling transport requires adopting either stochastic approaches that model heterogeneity explicitly or effective transport formulations that acknowledge the effects of heterogeneity. A number of such formulations have been developed and tested as upscaled representations of enhanced spreading. However, their ability to represent mixing has not been formally tested, which is required for proper reproduction of chemical reactions and which motivates our work. We propose that, for an effective transport formulation to be considered a valid representation of transport through Heterogeneous Porous Media (HPM, it should honor mean advection, mixing and spreading. It should also be flexible enough to be applicable to real problems. We test the capacity of the Multi-Rate Mass Transfer (MRMT to reproduce mixing observed in HPM, as represented by the classical multi-Gaussian log-permeability field with a Gaussian correlation pattern. Non-dispersive mixing comes from heterogeneity structures in the concentration fields that are not captured by macrodispersion. These fine structures limit mixing initially, but eventually enhance it. Numerical results show that, relative to HPM, MRMT models display a much stronger memory of initial conditions on mixing than on dispersion because of the sensitivity of the mixing state to the actual values of concentration. Because MRMT does not restitute the local concentration structures, it induces smaller non-dispersive mixing than HPM. However long-lived trapping in the immobile zones may sustain the deviation from dispersive mixing over much longer times. While spreading can be well captured by MRMT models, non-dispersive mixing cannot.

  20. Pore Scale Heterogeneity in the Mineral Distribution, Surface Area and Adsorption in Porous Rocks

    Science.gov (United States)

    Lai, P. E. P.; Krevor, S. C.

    2014-12-01

    The impact of heterogeneity in chemical transport and reaction is not understood in continuum (Darcy/Fickian) models of reactive transport. This is manifested in well-known problems such as scale dependent dispersion and discrepancies in reaction rate observations made at laboratory and field scales [1]. Additionally, this is a source of uncertainty for carbon dioxide injection, which produces a reactive fluid-rock system particularly in carbonate rock reservoirs. A potential cause is the inability of the continuum approach to incorporate the impact of heterogeneity in pore-scale reaction rates. This results in part from pore-scale heterogeneities in surface area of reactive minerals [2, 3]. We use x-ray micro tomography to describe the non-normal 3-dimensional distribution of reactive surface area within a porous medium according to distinct mineral groups. Using in-house image processing techniques, thin sections, nitrogen BET surface area, backscattered electron imaging and energy dispersive spectroscopy, we compare the surface area of each mineral phase to those obtained from x-ray CT imagery. In all samples, there is little correlation between the reactive surface area fraction and the volumetric fraction of a mineral in a bulk rock. Berea sandstone was far less heterogeneous and has a characteristic pore size at which a surface area distribution may be used to quantify heterogeneity. In carbonates, heterogeneity is more complex and surface area must be characterized at multiple length scales for an accurate description of reactive transport. We combine the mineral specific surface area characterisation to dynamic tomography, imaging the flow of water and solutes, to observe flow dependent and mineral specific adsorption. The observations may contribute to the incorporation of experimentally based statistical descriptions of pore scale heterogeneity in reactive transport into upscaled models, moving it closer to predictive capabilities for field scale

  1. Influence of temporal fluctuations and spatial heterogeneity on pollution transport in porous media

    OpenAIRE

    Elfeki, A. M. M.; Uffink, G.J.M.; Lebreton, S.

    2011-01-01

    The combined influence of temporal fluctuations and spatial heterogeneity on non-reactive solute transport mechanisms in porous media can be understood by performing simulations of steady and unsteady flow and transport in heterogeneous media. The study focuses on issues such as the degree of heterogeneity, correlation length, separation of the combined effects of temporal and spatial variations, and ergodicity conditions under unsteady flow conditions. It is shown that the effect of temporal...

  2. Compositional multiphase flow and transport in heterogeneous porous media

    Energy Technology Data Exchange (ETDEWEB)

    Huber, R.U.

    2000-07-01

    This work first treats the conceptual models for the description of multiphase flow processes in porous media. The thermodynamic laws are explained and the description and quantification of multi-fluid equilibria are discussed in order to account for fluid composition. The fully and weakly coupled approaches for the mathematical description of such flow processes with respect to systems consisting of two and three fluid phases as well as with respect to compositional single and multiphase systems are assessed. For the discretization of the two-phase flow equations node- and cell-centered finite volume methods and mixed and mixed-hybrid finite element approaches are applied. Based upon these methods five solution algorithms are developed. Four of these algorithms are based on the simultaneous solution of the discretized equations in combination with the Newton-Raphson technique. Methods 1 and 2 treat two- three-phase flow processes, Method 3 applies to the solution of partially miscible three-component systems while Method 4 is created for three-phase three-component systems. The latter method uses a variable substitution dependent on the local presence of the fluid phases. Method 5 is based on the IMPES/IMPESC concept. The time-implicit pressure equation is discretized with the mixed-hybrid finite element method. The saturation and concentration equations, respectively, are solved with a cell-centered finite volume scheme. The developed algorithms are applied to the two- and three-phase Buckley-Leverett problems. A partitioning interwell tracer test is simulated. The propagation behavior of nonaqueous phase liquids (NAPLs) in the saturated and unsaturated ground zone under the influence of heterogeneities are examined. In addition, a larger-scale experiment is simulated, which involves an injection of trichloroethylene into the subsurface and the subsequent distribution. Here, the development of a dissolved contaminant plume as well as the behavior of organic

  3. Chemical Sintering Generates Uniform Porous Hyaluronic Acid Hydrogels

    OpenAIRE

    Cam, Cynthia; Segura, Tatiana

    2013-01-01

    Implantation of scaffolds for tissue repair has been met with limited success primarily due to the inability to achieve vascularization within the construct. Many strategies have shifted to incorporate pores into these scaffolds to encourage rapid cellular infiltration and subsequent vascular ingrowth. We utilized an efficient chemical sintering technique to create a uniform network of polymethyl methacrylate (PMMA) microspheres for porous hyaluronic acid hydrogel formation. The porous hydrog...

  4. Dynamics of Coupled Contaminant and Microbial Transport in Heterogeneous Porous Media: Purdue Component. Final report

    International Nuclear Information System (INIS)

    Dynamic microbial attachment/detachment occurs in subsurface systems in response to changing environmental conditions caused by contaminant movement and degradation. Understanding the environmental conditions and mechanisms by which anaerobic bacteria partition between aqueous and solid phases is a critical requirement for designing and evaluating in situ bioremediation efforts. This interdisciplinary research project, of which we report only the Purdue contribution, provides fundamental information on the attachment/detachment dynamics of bacteria in heterogeneous porous media. Fundamental results from the Purdue collaboration are: (a) development of a matched-index method for obtaining 3-D Lagrangian trajectories of microbial sized particles transporting within porous media or microflow cells, (b) application of advanced numerical methods to optimally design a microflow cell for studying anaerobic bacterial attachment/detachment phenomena, (c) development of two types of models for simulating bacterial movement and attachment/detachment in microflow cells and natural porous media, (d) application of stochastic analysis to upscale pore scale microbial attachment/detachment models to natural heterogeneous porous media, and (e) evaluation of the role nonlocality plays in microbial dynamics in heterogeneous porous media

  5. Dynamics of Coupled Contaminant and Microbial Transport in Heterogeneous Porous Media: Purdue Component

    Energy Technology Data Exchange (ETDEWEB)

    Cushman, J.H.; Madilyn Fletcher

    2000-06-01

    Dynamic microbial attachment/detachment occurs in subsurface systems in response to changing environmental conditions caused by contaminant movement and degradation. Understanding the environmental conditions and mechanisms by which anaerobic bacteria partition between aqueous and solid phases is a critical requirement for designing and evaluating in situ bioremediation efforts. This interdisciplinary research project, of which we report only the Purdue contribution, provides fundamental information on the attachment/detachment dynamics of bacteria in heterogeneous porous media. Fundamental results from the Purdue collaboration are: (a) development of a matched-index method for obtaining 3-D Lagrangian trajectories of microbial sized particles transporting within porous media or microflow cells, (b) application of advanced numerical methods to optimally design a microflow cell for studying anaerobic bacterial attachment/detachment phenomena, (c) development of two types of models for simulating bacterial movement and attachment/detachment in microflow cells and natural porous media, (d) application of stochastic analysis to upscale pore scale microbial attachment/detachment models to natural heterogeneous porous media, and (e) evaluation of the role nonlocality plays in microbial dynamics in heterogeneous porous media

  6. Dynamics of Coupled Contaminant and Microbial Transport in Heterogeneous Porous Media: Purdue Component

    Energy Technology Data Exchange (ETDEWEB)

    Cushman, J.H.

    2000-06-01

    Dynamic microbial attachment/detachment occurs in subsurface systems in response to changing environmental conditions caused by contaminant movement and degradation. Understanding the environmental conditions and mechanisms by which anaerobic bacteria partition between aqueous and solid phases is a critical requirement for designing and evaluating in situ bioremediation efforts. This interdisciplinary research project, of which we report only the Purdue contribution, provides fundamental information on the attachment/detachment dynamics of bacteria in heterogeneous porous media. Fundamental results from the Purdue collaboration are: (a) development of a matched-index method for obtaining 3-D Lagrangian trajectories of microbial sized particles transporting within porous media or microflow cells, (b) application of advanced numerical methods to optimally design a microflow cell for studying anaerobic bacterial attachment/detachment phenomena, (c) development of two types of models for simulating bacterial movement and attachment/detachment in microflow cells and natural porous media, (d) application of stochastic analysis to upscale pore scale microbial attachment/detachment models to natural heterogeneous porous media, and (e) evaluation of the role nonlocality plays in microbial dynamics in heterogeneous porous media.

  7. Propagation behavior of permeability reduction in heterogeneous porous media due to particulate transport

    Science.gov (United States)

    Xu, Jianping

    2016-04-01

    In this letter we explore the propagation behavior of permeability reduction due to particulate transport in heterogeneous porous media. By simulating an advection-dispersion–based model we find that an attenuating sequence exists in terms of the propagation of particle concentration, permeability reduction and heterogeneity perturbation. The advancing speed of the fronts of the mentioned physical quantities attenuates successively from const to \\text{const}(1/n)1/t1-1/n to \\text{const}1/t (where n > 1 and t denotes time) regardless of the heterogeneity patterns. Then we move on to discuss the micro-dynamics of the propagation sequence, involving how it originates and how it connects with the macroscopic results. Moreover, exploiting the propagation mechanism enables us to know the condition under which we can apply the hypothesis of media homogeneity to describe the behavior of the particulate transport system in porous media.

  8. Initial conditions or emergence; what determines dissolution patterns in heterogeneous porous rocks?

    Science.gov (United States)

    Szymczak, Piotr; Upadhyay, Virat; Ladd, Anthony

    2016-04-01

    Dissolution of fractured or porous rocks is often accompanied by the formation of highly localized flow paths. Dissolution, in general, does not proceed uniformly, as it is influenced both by the heterogeneities in the rock matrix and by the instabilities associated with the positive feedback loops between the flow, dispersion, and chemical reactions. As a result, distinct channels or "wormholes" develop within the rocks in which both the flow and dissolution focus. In this communication, we aim to investigate how these emerging flow paths are influenced by the initial local inhomogeneities of the porosity field. Our results indicate a surprising insensitivity of the evolving dissolution patterns and flow rates to the amplitude and correlation length characterizing the inhomogeneities. At long times wormhole competition overwhelms the initial variations in aperture distribution, resulting in a universal relation between the separation of the wormholes and their length. This hierarchy of scales even persists in the presence of relatively large inhomogeneities (vugs), which focus the flow at the beginning of the dissolution process, but - if the sample is large enough - with time tend to be overwhelmed by the spontaneous growth of instabilities. A natural consequence of wormhole competition is that the separation between growing wormholes corresponds roughly to their length, something that is borne out by field observations.

  9. Multi-level adaptive simulation of transient two-phase flow in heterogeneous porous media

    KAUST Repository

    Chueh, C.C.

    2010-10-01

    An implicit pressure and explicit saturation (IMPES) finite element method (FEM) incorporating a multi-level shock-type adaptive refinement technique is presented and applied to investigate transient two-phase flow in porous media. Local adaptive mesh refinement is implemented seamlessly with state-of-the-art artificial diffusion stabilization allowing simulations that achieve both high resolution and high accuracy. Two benchmark problems, modelling a single crack and a random porous medium, are used to demonstrate the robustness of the method and illustrate the capabilities of the adaptive refinement technique in resolving the saturation field and the complex interaction (transport phenomena) between two fluids in heterogeneous media. © 2010 Elsevier Ltd.

  10. Dense, viscous brine behavior in heterogeneous porous medium systems.

    Science.gov (United States)

    Wright, D Johnson; Pedit, J A; Gasda, S E; Farthing, M W; Murphy, L L; Knight, S R; Brubaker, G R; Miller, C T

    2010-06-25

    The behavior of dense, viscous calcium bromide brine solutions used to remediate systems contaminated with dense nonaqueous phase liquids (DNAPLs) is considered in laboratory and field porous medium systems. The density and viscosity of brine solutions are experimentally investigated and functional forms fit over a wide range of mass fractions. A density of 1.7 times, and a corresponding viscosity of 6.3 times, that of water is obtained at a calcium bromide mass fraction of 0.53. A three-dimensional laboratory cell is used to investigate the establishment, persistence, and rate of removal of a stratified dense brine layer in a controlled system. Results from a field-scale experiment performed at the Dover National Test Site are used to investigate the ability to establish and maintain a dense brine layer as a component of a DNAPL recovery strategy, and to recover the brine at sufficiently high mass fractions to support the economical reuse of the brine. The results of both laboratory and field experiments show that a dense brine layer can be established, maintained, and recovered to a significant extent. Regions of unstable density profiles are shown to develop and persist in the field-scale experiment, which we attribute to regions of low hydraulic conductivity. The saturated-unsaturated, variable-density groundwater flow simulation code SUTRA is modified to describe the system of interest, and used to compare simulations to experimental observations and to investigate certain unobserved aspects of these complex systems. The model results show that the standard model formulation is not appropriate for capturing the behavior of sharp density gradients observed during the dense brine experiments. PMID:20444520

  11. Stochastic modeling of solute transport in 3-D heterogeneous porous media with random source condition

    OpenAIRE

    Chaudhuri, A; Sekhar, M.

    2006-01-01

    During probabilistic analysis of flow and transport in porous media, the uncertainty due to spatial heterogeneity of governing parameters are often taken into account. The randomness in the source conditions also play a major role on the stochastic behavior in distribution of the dependent variable. The present paper is focused on studying the effect of both uncertainty in the governing system parameters as well as the input source conditions. Under such circumstances, a method is proposed whic...

  12. Conversion of lignocellulose into renewable chemicals by heterogeneous catalysis

    OpenAIRE

    Kobayashi, Hirokazu; Ohta, Hidetoshi; Fukuoka, Atsushi

    2012-01-01

    Conversion of lignocellulose into renewable chemicals and fuels has received great attention for building up the sustainable societies. However, the utilisation of lignocellulose in the chemical industry has almost been limited for paper manufacturing because of the complicated chemical structure and persistent property of lignocellulose. Heterogeneous catalysis has the potential to selectively convert lignocellulosic biomasses into various useful chemicals, and this methodology has rapidly p...

  13. Electronic Chemical Potentials of Porous Metal–Organic Frameworks

    OpenAIRE

    Butler, Keith T.; Christopher H. Hendon; Walsh, Aron

    2014-01-01

    The binding energy of an electron in a material is a fundamental characteristic, which determines a wealth of important chemical and physical properties. For metal–organic frameworks this quantity is hitherto unknown. We present a general approach for determining the vacuum level of porous metal–organic frameworks and apply it to obtain the first ionization energy for six prototype materials including zeolitic, covalent, and ionic frameworks. This approach for valence band alignment can expla...

  14. Theory of the Kinetics of Chemical Potentials in Heterogeneous Catalysis

    OpenAIRE

    Cheng, Jun; Hu, P

    2011-01-01

    Simple and powerful: The reaction kinetics at surfaces of heterogeneous catalysts is reformulated in terms of the involved chemical potentials. Based on this formulism, an approach of searching for good catalysts is proposed without recourse to extensive calculations of reaction barriers and detailed kinetic analyses. (see picture; R=reactant, I=surface intermediate, P=product, and =standard chemical potential).

  15. Three-phase flow in heterogeneous wettability porous media; Deplacements triphasiques en milieux poreux de mouillabilite heterogene

    Energy Technology Data Exchange (ETDEWEB)

    Jaffrennou-Laroche, C.

    1998-11-26

    Better understanding and modelling of three-phase flow through porous media is of great interest, especially for improved oil recovery methods such as gas injection processes. Early theoretical and experimental studies have already demonstrated that the wettability characteristics of the solid surface and the spreading characteristics of the fluid system hold the key roles. This observation is confirmed by our theoretical results using DLP theory on the stability and the thickness of static oil films. In most of the works related to three-phase flow processes, homogeneous wettability is assumed. There exist only a few studies demonstrating the tremendous impact of the wettability heterogeneities on gas injection. The objective of the present work is twofold: to demonstrate the effect of small scale wettability heterogeneities on gas injection efficiency, and to develop a tool to predict this impact for various patterns and spatial distributions. To this end an experimental investigation in transparent glass micro-models is performed and a theoretical simulator is developed. Secondary and tertiary gas injections are performed for different heterogeneity patterns obtained by selective silane grafting. Displacement sequences are video-recorded and fluid saturations are determined by image analysis. Visualization of the displacement mechanisms provides the network model with the basic rules for water/oil and water/oil/gas motion. In water/oil displacement, drainage and imbibition occur according to the local wettability. Three-phase displacement is dominated by drainage mechanisms. The simulator allows the flow of oil through wetting films in the oil-wet regions and through spreading films on water in the water-wet regions. The effect of the wettability heterogeneities on: displacement mechanisms, sweep efficiency, and fluid distribution in three-phase gas injection is clearly demonstrated and successfully described by the network simulator. (author) 175 refs.

  16. Biphasic flow in a chemically active porous medium

    CERN Document Server

    Darmon, Alexandre; Salez, Thomas; Dauchot, Olivier

    2014-01-01

    We study the problem of the transformation of a given reactant species into an immiscible product species, as they flow through a chemically active porous medium. We derive the equation governing the evolution of the volume fraction of the species -- in a one-dimensional macroscopic description --, identify the relevant dimensionless numbers, and provide simple models for capillary pressure and relative permeabilities, which are quantities of crucial importance when tackling multiphase flows in porous media. We set the domain of validity of our models and discuss the importance of viscous coupling terms in the extended Darcy's law. We investigate numerically the steady regime and demonstrate that the spatial transformation rate of the species along the reactor is non-monotonous, as testified by the existence of an inflection point in the volume fraction profiles. We obtain the scaling of the location of this inflection point with the dimensionless lengths of the problem. Eventually, we provide key elements fo...

  17. Effective reaction rates for transport of particles to heterogeneous reactive (or porous) surfaces under shear

    Science.gov (United States)

    Shah, Preyas; Shaqfeh, Eric S. G.

    2015-11-01

    Mass transfer to heterogeneous reactive (or porous) surfaces is common in applications like heterogeneous catalysis, and biological porous media transport like drug delivery. This is modeled as advection-diffusion in a shear flow to an inert surface with first order reactive patches. We study transport of point particles using boundary element simulations. We show that the heterogeneous surface can be replaced with a uniform-flux boundary condition related to the Sherwood number (S), aka, the dimensionless flux to the reactive region. In the dilute limit of reactive regions, large-scale interaction between the reactive patches is important. In the dilute limit of inert regions, [S] grows as the reciprocal of the inert area fraction. Based on the method of resistances and numerical results, we provide correlations for [S] for general reactive surfaces and flow conditions. We model finite sized particles as general spheroids, specifically for biological applications. We do Brownian Dynamics simulations to account for hydrodynamic and steric interactions with the flow field and the domain geometry, and compare to the point particle results. We observe that anisotropic particles gave a higher pore transport flux compared to spherical particles at all flow conditions.

  18. Coulombic interactions and multicomponent ionic dispersion during transport of charged species in heterogeneous porous media

    DEFF Research Database (Denmark)

    Muniruzzaman, Muhammad; Rolle, Massimo

    Electrochemical cross-coupling plays a significant role for transport of charged species in porous media [1, 2]. In this study we performed flow-through experiments in a quasi two-dimensional setup using dilute solutions of strong electrolytes to study the influence of charge interactions on mass...... transfer of ionic species in saturated porous media. The experiments were carried out under advection-dominated conditions (seepage velocity: 1 and 1.5 m/day) in two well-defined heterogeneous domains where flow diverging around a low-permeability inclusion and flow focusing in high-permeability zones...... multicomponent transport simulations were compared with the high-resolution (5 mm spacing) concentration measurements of the ionic species at the outlet of the flow-through domain. The excellent agreement between the measured concentrations and the results of purely forward numerical simulations demonstrates the...

  19. Grayscale lattice Boltzmann model for multiphase heterogeneous flow through porous media

    Science.gov (United States)

    Pereira, Gerald G.

    2016-06-01

    The grayscale lattice Boltzmann (LB) model has been recently developed to model single-phase fluid flow through heterogeneous porous media. Flow is allowed in each voxel but the degree of flow depends on that voxel's resistivity to fluid motion. Here we extend the grayscale LB model to multiphase, immiscible flow. The new model is outlined and then applied to a number of test cases, which show good agreement with theory. This method is subsequently used to model the important case where each voxel may have a different resistance to each particular fluid that is passing through it. Finally, the method is applied to model fluid flow through real porous media to demonstrate its capability. Both the capillary and viscous flow regimes are recovered in these simulations.

  20. Value-added Chemicals from Biomass by Heterogeneous Catalysis

    DEFF Research Database (Denmark)

    Voss, Bodil

    been implemented. The subject on chemical production has received less attention. This thesis describes and evaluates the quest for an alternative conversion route, based on a biomass feedstock and employing a heterogeneous catalyst capable of converting the feedstock, to a value-added chemical. The...... obtained for such a process and the hypothesis that process feasibility in comparison with the conventional synthesis gas based technologies may further be attainable, taking advantage of the conservation of chemical C-C bonds in biomass based feedstocks. With ethanol as one example of a biomass based...... feedstock, having retained one C-C bond originating from the biomass precursor, the aspects of utilising heterogeneous catalysis for its conversion to value added chemicals is investigated. Through a simple analysis of known, but not industrialised catalytic routes, the direct conversion of ethanol to...

  1. Transverse mixing in three-dimensional nonstationary anisotropic heterogeneous porous media

    DEFF Research Database (Denmark)

    Cirpka, Olaf; Chiogna, Gabriele; Rolle, Massimo;

    2015-01-01

    Groundwater plumes originating from continuously emitting sources are typically controlled by transverse mixing between the plume and reactants in the ambient solution. In two-dimensional domains, heterogeneity causes only weak enhancement of transverse mixing in steady-state flows. In three......-dimensional domains, more complex flow patterns are possible because streamlines can twist. In particular, spatially varying orientation of anisotropy can cause steady-state groundwater whirls. We analyze steady-state solute transport in three-dimensional locally isotropic heterogeneous porous media with blockwise...... anisotropic correlation structure, in which the principal directions of anisotropy differ from block to block. For this purpose, we propose a transport scheme that relies on advective transport along streamlines and transverse-dispersive mass exchange between them based on Voronoi tessellation. We compare...

  2. Heterogeneous nucleation of ice from supercooled NaCl solution confined in porous cement paste

    Science.gov (United States)

    Zeng, Qiang; Li, Kefei; Fen-Chong, Teddy

    2015-01-01

    Clarifying the nucleation process of chloride-based deicing salt solution (e.g., NaCl solution) confined in cement-based porous materials remains an important issue to understand its detrimental effects on material substrates. In this study, the pore structures of hardened cement pastes were characterized by mercury-intrusion and nitrogen-sorption porosimetry. The ice nucleation temperature of NaCl solution of different concentrations confined in the hardened cement pastes was measured and analyzed by classical heterogeneous nucleation theory. The kinetic factor, contact-angle factor including the contact angle between ice and the substrate were evaluated. The results revealed that the contact angle between ice and the substrate showed the minimum value when adding 3% NaCl into water. The heterogeneous ice nucleation rates were found to be proportional to the water activity shifts.

  3. Study on Two-Phase Flow in Heterogeneous Porous Media by Light Transmission Method

    Science.gov (United States)

    Qiao, W.

    2015-12-01

    The non-aqueous phase liquid (NAPL) released to the subsurface can form residual ganglia and globules occupying pores and also accumulate and form pools, in which multiphase system forms. Determining transient fluid saturations in a multiphase system is essential to understand the flow characteristics of systems and to perform effective remediation strategies. As a non-destructive and non-invasive laboratory technique utilized for the measurement of liquid saturation in porous media, light transmission is of the lowest cost and safe. Utilization of Coupled Charge Device camera in light transmission systems provides a nearly instantaneous high-density array of spatial measurements over a very large dynamic range. The migration of NAPL and air spariging technique applied to remove NAPL in aquifer systems are typically two-phase flow problem. Because of the natural aquifer normally being heterogeneous, two 2-D sandboxes (Length55cm×width1.3cm×hight45cm) are set up to study the migration of gas and DNAPL in heterogeneous porous media based on light transmission method and its application in two-phase flow. Model D for water/gas system developed by Niemet and Selker (2001) and Model NW-A for water/NAPL system developed by Zhang et al. (2014) are applied for the calculation of fluid saturation in the two experiments, respectively. The gas injection experiments show that the gas moves upward in the irregular channels, piling up beneath the low permeability lenses and starting lateral movement. Bypassing the lenses, the gas moves upward and forms continuous distribution in the top of the sandbox. The faster of gas injects, the wider of gas migration will be. The DNAPL infiltration experiment shows that TCE mainly moves downward as the influence of gravity, stopping vertical infiltration when reaching the low permeability lenses because of its failure to overcome the capillary pressure. Then, TCE accumulates on the surface and starts transverse movement. Bypassing the

  4. Simulation of density-driven flow in heterogeneous and fractured porous media

    Energy Technology Data Exchange (ETDEWEB)

    Grillo, A. [Politecnico di Torino (Italy). DISMA; Logashenko, D. [Steinbeis Research Center, Oelbronn (Germany); Stichel, S.; Wittum, G. [Frankfurt Univ., Frankfurt am Main (Germany). G-CSC

    2015-07-01

    The study of fractured porous media is an important and challenging problem in hydrogeology. One of the difficulties is that mathematical models have to account for heterogeneity introduced by fractures in hydrogeological media. Heterogeneity may strongly influence the physical processes taking place in these media. Moreover, the thickness of the fractures, which is usually negligible in comparison with the size of the whole domain, and the complicated geometry of fracture networks reduce essentially the efficiency of numerical methods. In order to overcome these difficulties, fractures are sometimes considered as objects of reduced dimensionality (surfaces in three dimensions), and the field equations are averaged along the fracture width. Fractures are assumed to be thin regions of space filled with a porous material whose properties differ from those of the porous medium enclosing them. The interfaces separating the fractures from the embedding medium are assumed to be ideal. We consider two approaches: (i) the fractures have the same dimension, d, as the embedding medium and are said to be d-dimensional; (ii) the fractures are considered as (d-1)-dimensional manifolds, and the equations of density-driven flow are found by averaging the d-dimensional laws over the fracture width. We show that the second approach is a valid alternative to the first one. For this purpose, we perform numerical experiments using a finite-volume discretization for both approaches. The results obtained by the two methods are in good agreement with each other. We derive a criterion for the validity of the simplified representation. The criterion characterizes the transition of a mainly parallel flow to a rotational flow, which cannot be reasonably approximated using a d-1 dimensional representation. We further present a numerical algorithm using adaptive dimensional representation.

  5. Energy-Based Spatial Weighting Functions and Equivalent Hydraulic Conductivity in Heterogeneous Porous Media.

    Science.gov (United States)

    Molz, F. J.; Guan, J.

    2004-12-01

    To improve understanding of property measurements in heterogeneous media, an energy-based weighting function concept was developed [Molz et al., WRR, 39(4), DAN-1, 2003]. In (assumed) homogeneous media, the instrument spatial weighting function (ISWF) depends only on the energy dissipation distribution set up by the measurement procedure, and it reduces to simply inverse sample volume (uniform weighting) for the 1-D parallel flow case (ideal permeameter). For 1-D transient flow in homogeneous media, such as with slug tests, the ISWF varies with position and time, with 95% of the total weighting contained within 115 well radii, even late in the test [Molz et al., Ground Water, in press, 2004]. The present talk deals with the heterogeneous case, which is what one deals with in natural systems. Thus, in actual measurements, the identification of the ISWF is connected to the problem of determining an "equivalent" hydraulic conductivity (Ke), and it would be ideal if the criterion for "equivalence" based on energy-dissipation- rate-weighting would produce the same Ke as that based on the common permeameter test. It can be shown that for 1-D linear and radial flow in heterogeneous porous media, the energy-dissipation based Ke and the usual Ke calculated using assumed homogeneity and Darcy's law are identical. We will explore whether this same equivalence holds in general for 2-D and 3-D heterogeneity. The results to date imply that as one makes K measurements in heterogeneous media at different locations or on different cores of heterogeneous materials, the ISWF will be heterogeneity-dependent, implying that the averaging process resulting in the "equivalent" K value also varies with position. If the testing procedure is transient, then the averaging process varies also with time. This suggests a fundamental ambiguity in the interpretation of hydraulic conductivity measurements in heterogeneous media that may impact how we approach modeling and prediction in a practical

  6. Exposure-time based modeling of nonlinear reactive transport in porous media subject to physical and geochemical heterogeneity

    Science.gov (United States)

    Sanz-Prat, Alicia; Lu, Chuanhe; Amos, Richard T.; Finkel, Michael; Blowes, David W.; Cirpka, Olaf A.

    2016-09-01

    Transport of reactive solutes in groundwater is affected by physical and chemical heterogeneity of the porous medium, leading to complex spatio-temporal patterns of concentrations and reaction rates. For certain cases of bioreactive transport, it could be shown that the concentrations of reactive constituents in multi-dimensional domains are approximately aligned with isochrones, that is, lines of identical travel time, provided that the chemical properties of the matrix are uniform. We extend this concept to combined physical and chemical heterogeneity by additionally considering the time that a water parcel has been exposed to reactive materials, the so-called exposure time. We simulate bioreactive transport in a one-dimensional domain as function of time and exposure time, rather than space. Subsequently, we map the concentrations to multi-dimensional heterogeneous domains by means of the mean exposure time at each location in the multi-dimensional domain. Differences in travel and exposure time at a given location are accounted for as time difference. This approximation simplifies reactive-transport simulations significantly under conditions of steady-state flow when reactions are restricted to specific locations. It is not expected to be exact in realistic applications because the underlying assumption, such as neglecting transverse mixing altogether, may not hold. We quantify the error introduced by the approximation for the hypothetical case of a two-dimensional, binary aquifer made of highly-permeable, non-reactive and low-permeable, reactive materials releasing dissolved organic matter acting as electron donor for aerobic respiration and denitrification. The kinetically controlled reactions are catalyzed by two non-competitive bacteria populations, enabling microbial growth. Even though the initial biomass concentrations were uniform, the interplay between transport, non-uniform electron-donor supply, and bio-reactions led to distinct spatial patterns of

  7. Multiscale Lattice Boltzmann method for flow simulations in highly heterogenous porous media

    KAUST Repository

    Li, Jun

    2013-01-01

    A lattice Boltzmann method (LBM) for flow simulations in highly heterogeneous porous media at both pore and Darcy scales is proposed in the paper. In the pore scale simulations, flow of two phases (e.g., oil and gas) or two immiscible fluids (e.g., water and oil) are modeled using cohesive or repulsive forces, respectively. The relative permeability can be computed using pore-scale simulations and seamlessly applied for intermediate and Darcy-scale simulations. A multiscale LBM that can reduce the computational complexity of existing LBM and transfer the information between different scales is implemented. The results of coarse-grid, reduced-order, simulations agree very well with the averaged results obtained using fine grid.

  8. Impact of biofilm-induced heterogeneities on solute transport in porous media

    Science.gov (United States)

    Kone, T.; Golfier, F.; Orgogozo, L.; Oltéan, C.; Lefèvre, E.; Block, J. C.; Buès, M. A.

    2014-11-01

    In subsurface systems, biofilm may degrade organic or organometallic pollutants contributing to natural attenuation and soil bioremediation techniques. This increase of microbial activity leads to change the hydrodynamic properties of aquifers. The purpose of this work was to investigate the influence of biofilm-induced heterogeneities on solute transport in porous media and more specifically on dispersivity. We pursued this goal by (i) monitoring both spatial concentration fields and solute breakthrough curves from conservative tracer experiments in a biofilm-supporting porous medium, (ii) characterizing in situ the changes in biovolume and visualizing the dynamics of the biological material at the mesoscale. A series of experiments was carried out in a flow cell system (60 cm3) with a silica sand (Φ = 50-70 mesh) as solid carrier and Shewanella oneidensis MR-1 as bacterial strain. Biofilm growth was monitored by image acquisition with a digital camera. The biofilm volume fraction was estimated through tracer experiments with the Blue Dextran macromolecule as in size-exclusion chromatography, leading to a fair picture of the biocolonization within the flow cell. Biofilm growth was achieved in the whole flow cell in 29 days and up to 50% of void space volume was plugged. The influence of biofilm maturation on porous medium transport properties was evaluated from tracer experiments using Brilliant Blue FCF. An experimental correlation was found between effective (i.e., nonbiocolonized) porosity and biofilm-affected dispersivity. Comparison with values given by the theoretical model of Taylor and Jaffé (1990b) yields a fair agreement.

  9. Algebraic multiscale method for flow in heterogeneous porous media with embedded discrete fractures (F-AMS)

    Science.gov (United States)

    Ţene, Matei; Al Kobaisi, Mohammed Saad; Hajibeygi, Hadi

    2016-09-01

    This paper introduces an Algebraic MultiScale method for simulation of flow in heterogeneous porous media with embedded discrete Fractures (F-AMS). First, multiscale coarse grids are independently constructed for both porous matrix and fracture networks. Then, a map between coarse- and fine-scale is obtained by algebraically computing basis functions with local support. In order to extend the localization assumption to the fractured media, four types of basis functions are investigated: (1) Decoupled-AMS, in which the two media are completely decoupled, (2) Frac-AMS and (3) Rock-AMS, which take into account only one-way transmissibilities, and (4) Coupled-AMS, in which the matrix and fracture interpolators are fully coupled. In order to ensure scalability, the F-AMS framework permits full flexibility in terms of the resolution of the fracture coarse grids. Numerical results are presented for two- and three-dimensional heterogeneous test cases. During these experiments, the performance of F-AMS, paired with ILU(0) as second-stage smoother in a convergent iterative procedure, is studied by monitoring CPU times and convergence rates. Finally, in order to investigate the scalability of the method, an extensive benchmark study is conducted, where a commercial algebraic multigrid solver is used as reference. The results show that, given an appropriate coarsening strategy, F-AMS is insensitive to severe fracture and matrix conductivity contrasts, as well as the length of the fracture networks. Its unique feature is that a fine-scale mass conservative flux field can be reconstructed after any iteration, providing efficient approximate solutions in time-dependent simulations.

  10. Global-local nonlinear model reduction for flows in heterogeneous porous media

    KAUST Repository

    Alotaibi, Manal

    2015-08-01

    In this paper, we combine discrete empirical interpolation techniques, global mode decomposition methods, and local multiscale methods, such as the Generalized Multiscale Finite Element Method (GMsFEM), to reduce the computational complexity associated with nonlinear flows in highly-heterogeneous porous media. To solve the nonlinear governing equations, we employ the GMsFEM to represent the solution on a coarse grid with multiscale basis functions and apply proper orthogonal decomposition on a coarse grid. Computing the GMsFEM solution involves calculating the residual and the Jacobian on a fine grid. As such, we use local and global empirical interpolation concepts to circumvent performing these computations on the fine grid. The resulting reduced-order approach significantly reduces the flow problem size while accurately capturing the behavior of fully-resolved solutions. We consider several numerical examples of nonlinear multiscale partial differential equations that are numerically integrated using fully-implicit time marching schemes to demonstrate the capability of the proposed model reduction approach to speed up simulations of nonlinear flows in high-contrast porous media.

  11. Wave propagation in a strongly heterogeneous elastic porous medium: Homogenization of Biot medium with double porosities

    Science.gov (United States)

    Rohan, Eduard; Naili, Salah; Nguyen, Vu-Hieu

    2016-08-01

    We study wave propagation in an elastic porous medium saturated with a compressible Newtonian fluid. The porous network is interconnected whereby the pores are characterized by two very different characteristic sizes. At the mesoscopic scale, the medium is described using the Biot model, characterized by a high contrast in the hydraulic permeability and anisotropic elasticity, whereas the contrast in the Biot coupling coefficient is only moderate. Fluid motion is governed by the Darcy flow model extended by inertia terms and by the mass conservation equation. The homogenization method based on the asymptotic analysis is used to obtain a macroscopic model. To respect the high contrast in the material properties, they are scaled by the small parameter, which is involved in the asymptotic analysis and characterized by the size of the heterogeneities. Using the estimates of wavelengths in the double-porosity networks, it is shown that the macroscopic descriptions depend on the contrast in the static permeability associated with pores and micropores and on the frequency. Moreover, the microflow in the double porosity is responsible for fading memory effects via the macroscopic poroviscoelastic constitutive law. xml:lang="fr"

  12. Active targeting in a random porous medium by chemical swarm robots with secondary chemical signaling

    Science.gov (United States)

    Grančič, Peter; Štěpánek, František

    2011-08-01

    The multibody dynamics of a system of chemical swarm robots in a porous environment is investigated. The chemical swarm robots are modeled as Brownian particles capable of delivering an encapsulated chemical payload toward a given target location and releasing it in response to an external stimulus. The presence of chemical signals (chemo-attractant) in the system plays a crucial role in coordinating the collective movement of the particles via chemotaxis. For a number of applications, such as distributed chemical processing and targeted drug delivery, the understanding of factors that govern the collective behavior of the particles, especially their ability to localize a given target, is of immense importance. A hybrid modeling methodology based on the combination of the Brownian dynamics method and diffusion problem coupled through the chemotaxis phenomena is used to analyze the impact of a varying signaling threshold and the strength of chemotaxis on the ability of the chemical robots to fulfill their target localization mission. The results demonstrate that the selected performance criteria (the localization half time and the success rate) can be improved when an appropriate signaling process is chosen. Furthermore, for an optimum target localization strategy, the topological complexity of the porous environment needs to be reflected.

  13. A new approach to tracer transport analysis: From fracture systems to strongly heterogeneous porous media

    Energy Technology Data Exchange (ETDEWEB)

    Tsang, Chin-Fu

    1989-02-01

    Many current development and utilization of groundwater resources include a study of their flow and transport properties. These properties are needed in evaluating possible changes in groundwater quality and potential transport of hazardous solutes through the groundwater system. Investigation of transport properties of fractured rocks is an active area of research. Most of the current approaches to the study of flow and transport in fractured rocks cannot be easily used for analysis of tracer transport field data. A new approach is proposed based on a detailed study of transport through a fracture of variable aperture. This is a two-dimensional strongly heterogeneous permeable system. It is suggested that tracer breakthrough curves can be analyzed based on an aperture or permeability probability distribution function that characterizes the tracer flow through the fracture. The results are extended to a multi-fracture system and can be equally applied to a strongly heterogeneous porous medium. Finally, the need for multi-point or line and areal tracer injection and observation tests is indicated as a way to avoid the sensitive dependence of point measurements on local permeability variability. 30 refs., 15 figs.

  14. Chemical stabilization of porous silicon for enhanced biofunctionalization with immunoglobulin

    Directory of Open Access Journals (Sweden)

    Nelson Naveas, Vicente Torres Costa, Dario Gallach, Jacobo Hernandez-Montelongo, Raul Jose Martín Palma, Josefa Predenstinacion Garcia-Ruiz and Miguel Manso-Silván

    2012-01-01

    Full Text Available Porous silicon (PSi is widely used in biological experiments, owing to its biocompatibility and well-established fabrication methods that allow tailoring its surface. Nevertheless, there are some unresolved issues such as deciding whether the stabilization of PSi is necessary for its biological applications and evaluating the effects of PSi stabilization on the surface biofunctionalization with proteins. In this work we demonstrate that non-stabilized PSi is prone to detachment owing to the stress induced upon biomolecular adsorption. Biofunctionalized non-stabilized PSi loses the interference properties characteristic of a thin film, and groove-like structures resulting from a final layer collapse were observed by scanning electron microscopy. Likewise, direct PSi derivatization with 3-aminopropyl-triethoxysilane (APTS does not stabilize PSi against immunoglobulin biofunctionalization. To overcome this problem, we developed a simple chemical process of stabilizing PSi (CoxPSi for biological applications, which has several advantages over thermal stabilization (ToxPSi. The process consists of chemical oxidation in H2O2, surface derivatization with APTS and a curing step at 120 °C. This process offers integral homogeneous PSi morphology, hydrophilic surface termination (contact angle θ = 26° and highly efficient derivatized and biofunctionalized PSi surfaces (six times more efficient than ToxPSi. All these features are highly desirable for biological applications, such as biosensing, where our results can be used for the design and optimization of the biomolecular immobilization cascade on PSi surfaces.

  15. Factors affecting gas migration and contaminant redistribution in heterogeneous porous media subject to electrical resistance heating

    Science.gov (United States)

    Munholland, Jonah L.; Mumford, Kevin G.; Kueper, Bernard H.

    2016-01-01

    A series of intermediate-scale laboratory experiments were completed in a two-dimensional flow cell to investigate gas production and migration during the application of electrical resistance heating (ERH) for the removal of dense non-aqueous phase liquids (DNAPLs). Experiments consisted of heating water in homogeneous silica sand and heating 270 mL of trichloroethene (TCE) and chloroform (CF) DNAPL pools in heterogeneous silica sands, both under flowing groundwater conditions. Spatial and temporal distributions of temperature were measured using thermocouples and observations of gas production and migration were collected using front-face image capture throughout the experiments. Post-treatment soil samples were collected and analyzed to assess DNAPL removal. Results of experiments performed in homogeneous sand subject to different groundwater flow rates showed that high groundwater velocities can limit subsurface heating rates. In the DNAPL pool experiments, temperatures increased to achieve DNAPL-water co-boiling, creating estimated gas volumes of 131 and 114 L that originated from the TCE and CF pools, respectively. Produced gas migrated vertically, entered a coarse sand lens and subsequently migrated laterally beneath an overlying capillary barrier to outside the heated treatment zone where 31-56% of the original DNAPL condensed back into a DNAPL phase. These findings demonstrate that layered heterogeneity can potentially facilitate the transport of contaminants outside the treatment zone by mobilization and condensation of gas phases during ERH applications. This underscores the need for vapor phase recovery and/or control mechanisms below the water table during application of ERH in heterogeneous porous media during the co-boiling stage, which occurs prior to reaching the boiling point of water.

  16. Modeling tracer transport in randomly heterogeneous porous media by nonlocal moment equations: Anomalous transport

    Science.gov (United States)

    Morales-Casique, E.; Lezama-Campos, J. L.; Guadagnini, A.; Neuman, S. P.

    2013-05-01

    Modeling tracer transport in geologic porous media suffers from the corrupt characterization of the spatial distribution of hydrogeologic properties of the system and the incomplete knowledge of processes governing transport at multiple scales. Representations of transport dynamics based on a Fickian model of the kind considered in the advection-dispersion equation (ADE) fail to capture (a) the temporal variation associated with the rate of spreading of a tracer, and (b) the distribution of early and late arrival times which are often observed in field and/or laboratory scenarios and are considered as the signature of anomalous transport. Elsewhere we have presented exact stochastic moment equations to model tracer transport in randomly heterogeneous aquifers. We have also developed a closure scheme which enables one to provide numerical solutions of such moment equations at different orders of approximations. The resulting (ensemble) average and variance of concentration fields were found to display a good agreement against Monte Carlo - based simulation results for mildly heterogeneous (or well-conditioned strongly heterogeneous) media. Here we explore the ability of the moment equations approach to describe the distribution of early arrival times and late time tailing effects which can be observed in Monte-Carlo based breakthrough curves (BTCs) of the (ensemble) mean concentration. We show that BTCs of mean resident concentration calculated at a fixed space location through higher-order approximations of moment equations display long tailing features of the kind which is typically associated with anomalous transport behavior and are not represented by an ADE model with constant dispersive parameter, such as the zero-order approximation.

  17. Massively Parallel Geostatistical Inversion of Coupled Processes in Heterogeneous Porous Media

    Science.gov (United States)

    Ngo, A.; Schwede, R. L.; Li, W.; Bastian, P.; Ippisch, O.; Cirpka, O. A.

    2012-04-01

    The quasi-linear geostatistical approach is an inversion scheme that can be used to estimate the spatial distribution of a heterogeneous hydraulic conductivity field. The estimated parameter field is considered to be a random variable that varies continuously in space, meets the measurements of dependent quantities (such as the hydraulic head, the concentration of a transported solute or its arrival time) and shows the required spatial correlation (described by certain variogram models). This is a method of conditioning a parameter field to observations. Upon discretization, this results in as many parameters as elements of the computational grid. For a full three dimensional representation of the heterogeneous subsurface it is hardly sufficient to work with resolutions (up to one million parameters) of the model domain that can be achieved on a serial computer. The forward problems to be solved within the inversion procedure consists of the elliptic steady-state groundwater flow equation and the formally elliptic but nearly hyperbolic steady-state advection-dominated solute transport equation in a heterogeneous porous medium. Both equations are discretized by Finite Element Methods (FEM) using fully scalable domain decomposition techniques. Whereas standard conforming FEM is sufficient for the flow equation, for the advection dominated transport equation, which rises well known numerical difficulties at sharp fronts or boundary layers, we use the streamline diffusion approach. The arising linear systems are solved using efficient iterative solvers with an AMG (algebraic multigrid) pre-conditioner. During each iteration step of the inversion scheme one needs to solve a multitude of forward and adjoint problems in order to calculate the sensitivities of each measurement and the related cross-covariance matrix of the unknown parameters and the observations. In order to reduce interprocess communications and to improve the scalability of the code on larger clusters

  18. Chemical heterogeneities in the mantle: The equilibrium thermodynamic approach

    Science.gov (United States)

    Tirone, M.; Buhre, S.; Schmück, H.; Faak, K.

    2016-02-01

    This study attempts to answer a simple and yet fundamental question in relation to our understanding of the chemical evolution of deep Earth and planetary interiors. Given two initially separate assemblages (lithologies) in chemical equilibrium can we predict the chemical and mineralogical compositions of the two assemblages when they are put together to form a new equilibrated system? Perhaps a common perception is that given sufficient time, the two assemblages will homogenize chemically and mineralogically, however from a chemical thermodynamic point of view, this is not the case. Certain petrological differences in terms of bulk composition, mineralogy and mineral abundance remain unless other processes, like melting or mechanical mixing come into play. While there is not a standard procedure to address this problem, in this study it is shown that by applying chemical thermodynamic principles and some reasonable assumptions, it is possible to determine the equilibrium composition of each of the two assemblages. Some examples that consider typical mantle rocks, peridotite, lherzolite, dunite and eclogite described by simplified chemical systems are used to illustrate the general approach. A preliminary application to evaluate the effect of melting a heterogeneous mantle in complete chemical equilibrium using a thermodynamic formulation coupled with a two-phase geodynamic model shows that major element composition of the melt product generated by different peridotites is very similar. This may explain the relative homogeneity of major elements of MORBs which could be the product of melting a relatively uniform mantle, as commonly accepted, or alternatively a peridotitic mantle with different compositions but in chemical equilibrium.

  19. Chemical Modification of Porous Alumina for Nanowire Templating and NEXAFS Spectroscopy of Aqueous ATP

    OpenAIRE

    Kelly, Daniel Nicholas

    2010-01-01

    Part One: Chemical Modification of Porous Alumina for Nanowire Templating: A modified sol-gel technique and subsequent polymer coating technique was used to modify the size of nanowires grown via electrodeposition in porous alumina templates. The porous alumina film is initially soaked in a water-containing solution prior to exposure to a different solution of 3-aminopropyltriethoxysilane in toluene. The amount of water in the aqueous solution correlates with the thickness of silane coating ...

  20. A global method for coupling transport with chemistry in heterogeneous porous media

    CERN Document Server

    Laila, Amir; 10.1007/s10596-009-9162-x

    2009-01-01

    Modeling reactive transport in porous media, using a local chemical equilibrium assumption, leads to a system of advection-diffusion PDE's coupled with algebraic equations. When solving this coupled system, the algebraic equations have to be solved at each grid point for each chemical species and at each time step. This leads to a coupled non-linear system. In this paper a global solution approach that enables to keep the software codes for transport and chemistry distinct is proposed. The method applies the Newton-Krylov framework to the formulation for reactive transport used in operator splitting. The method is formulated in terms of total mobile and total fixed concentrations and uses the chemical solver as a black box, as it only requires that on be able to solve chemical equilibrium problems (and compute derivatives), without having to know the solution method. An additional advantage of the Newton-Krylov method is that the Jacobian is only needed as an operator in a Jacobian matrix times vector product...

  1. Chemical heterogeneities in the interior of terrestrial bodies

    Science.gov (United States)

    Plesa, Ana-Catalina; Maurice, Maxime; Tosi, Nicola; Breuer, Doris

    2016-04-01

    Mantle chemical heterogeneities that can strongly influence the interior dynamics have been inferred for all terrestrial bodies of the Solar System and range from local to global scale. Seismic data for the Earth, differences in surface mineral compositions observed in data sets from space missions, and isotopic variations identified in laboratory analyses of meteorites or samples indicate chemically heterogeneous systems. One way to generate large scale geochemical heterogeneities is through the fractional crystallization of a liquid magma ocean. The large amount of energy available in the early stages of planetary evolution can cause melting of a significant part or perhaps even the entire mantle of a terrestrial body resulting in a liquid magma ocean. Assuming fractional crystallization, magma ocean solidification proceeds from the core-mantle boundary to the surface where dense cumulates tend to form due to iron enrichment in the evolving liquid. This process leads to a gravitationally unstable mantle, which is prone to overturn. Following cumulate overturn, a stable stratification may be reached that prevents efficient material transport. As a consequence, mantle reservoirs may be kept separate, possibly for the entire thermo-chemical evolution of a terrestrial body. Scenarios assuming fractional crystallization of a liquid magma ocean have been suggested to explain lavas with distinct composition on Mercury's surface [1], the generation of the Moon's mare basalts by sampling a reservoir consisting of overturned ilmenite-bearing cumulates [2], and the preservation of Mars' geochemical reservoirs as inferred by isotopic analysis of the SNC meteorites [3]. However, recent studies have shown that the style of the overturn as well as the subsequent density stratification are of extreme importance for the subsequent thermo-chemical evolution of a planetary body and may have a major impact on the later surface tectonics and volcanic history. The rapid formation of a

  2. Chemically modified and nanostructured porous silicon as a drug delivery material and device

    Science.gov (United States)

    Anglin, Emily Jessica

    This thesis describes the fabrication, chemical modification, drug release, and toxicity studies of nanostructured porous silicon for the purposes of developing a smart drug delivery device. The first chapter is an introductory chapter, presenting the chemical and physical properties of porous silicon, the concepts and issues of current drug delivery devices and materials, and how porous silicon can address the issues regarding localized and controlled drug therapies. The second chapter discusses chemical modifications of nanostructured porous Si for stabilizing the material in biologically relevant media while providing an extended release of a therapeutic in vitro. This chapter also demonstrates the utility of the porous silicon optical signatures for effectively monitoring drug release from the system and its applications for development of a self-reporting drug delivery device. In chapter three, the concept of providing a triggered release of a therapeutic from porous silicon microparticles through initiation by an external stimulus is demonstrated. The microparticles are chemically modified, and the release is enhanced by a short application of ultrasound to the particulate system. The effect of ultrasound on the drug release and particle size is discussed. Chapter four presents a new method for sustaining the release of a monoclonal antibody from the porous matrix of porous SiO2. The therapeutic is incorporated into the films through electrostatic adsorption and a slow release is observed in vitro. A new method of quantifying the extent of drug loading is monitored with interferometry. The last chapter of the thesis provides a basic in vivo toxicity study of various porous Si microparticles for intraocular applications. Three types of porous Si particles are fabricated and studied in a rabbit eye model. The toxicity studies were conducted by collaborators at the Shiley Eye Center, La Jolla, CA. This work, demonstrates the feasibility of developing a self

  3. Complexity reduction of multi-phase flows in heterogeneous porous media

    KAUST Repository

    Ghommem, Mehdi

    2013-01-01

    In this paper, we apply mode decomposition and interpolatory projection methods to speed up simulations of two-phase flows in highly heterogeneous porous media. We propose intrusive and non-intrusive model reduction approaches that enable a significant reduction in the dimension of the flow problem size while capturing the behavior of the fully-resolved solutions. In one approach, we employ the dynamic mode decomposition (DMD) and the discrete empirical interpolation method (DEIM). This approach does not require any modification of the reservoir simulation code but rather postprocesses a set of global snapshots to identify the dynamically-relevant structures associated with the flow behavior. In a second approach, we project the governing equations of the velocity and the pressure fields on the subspace spanned by their proper orthogonal decomposition (POD) modes. Furthermore, we use DEIM to approximate the mobility related term in the global system assembly and then reduce the online computational cost and make it independent of the fine grid. To show the effectiveness and usefulness of the aforementioned approaches, we consider the SPE 10 benchmark permeability field and present a variety of numerical examples of two-phase flow and transport. The proposed model reduction methods can be efficiently used when performing uncertainty quantification or optimization studies and history matching.

  4. Practical chemical analysis of Pt and Pd based heterogeneous catalysts with hard X-ray photoelectron spectroscopy

    International Nuclear Information System (INIS)

    Highlights: •Hard X-ray photoelectron spectroscopy (HAXPES) enables interface analysis of catalyst. •HAXPES enables overall analysis of porous film of Pt-doped CeO2 and related catalyst. •HAXPES enables analysis of trace elements for Pd and Pt3Ni nanoparticle catalysts. -- Abstract: Interfacial properties including configuration, porosity, chemical states, and atomic diffusion greatly affect the performance of supported heterogeneous catalysts. Hard X-ray photoelectron spectroscopy (HAXPES) can be used to analyze the interfaces of heterogeneous catalysts because of its large information depth of more than 20 nm. We use HAXPES to examine Pt-doped CeO2 and related thin film catalysts evaporated on Si, carbon, and carbon nanotube substrates, because Pt-doped CeO2 has great potential as a noble metal-based heterogeneous catalyst for fuel cells. The HAXPES measurements clarify that the dopant material, substrate material, and surface pretreatment of substrate are important parameters that affect the interfacial properties of Pt-doped CeO2 and related thin film catalysts. Another advantage of HAXPES measurement of heterogeneous catalysts is that it can be used for chemical analysis of trace elements by detecting photoelectrons from deep core levels, which have large photoionization cross-sections in the hard X-ray region. We use HAXPES for chemical analysis of trace elements in Pd nanoparticle catalysts immobilized on sulfur-terminated substrates and Pt3Ni nanoparticle catalysts enveloped by dendrimer molecules

  5. Novel real function based method to construct heterogeneous porous scaffolds and additive manufacturing for use in medical engineering.

    Science.gov (United States)

    Yang, Nan; Tian, Yanling; Zhang, Dawei

    2015-11-01

    Heterogeneous porous scaffolds have important applications in biomedical engineering, as they can mimic the structures of natural tissues to achieve the corresponding properties. Here, we introduce a new and easy to implement real function based method for constructing complex, heterogeneous porous structures, including hybrid structures, stochastic structures, functionally gradient structures, and multi-scale structures, or their combinations (e.g., hybrid multi-scale structures). Based on micro-CT data, a femur-mimetic structure with gradient morphology was constructed using our method and fabricated using stereolithography. Results showed that our method could generate gradient porosity or gradient specific surfaces and be sufficiently flexible for use with micro-CT data and additive manufacturing (AM) techniques. PMID:26320819

  6. Dynamic transverse shear modulus for a heterogeneous fluid-filled porous solid containing cylindrical inclusions

    Science.gov (United States)

    Song, Yongjia; Hu, Hengshan; Rudnicki, John W.; Duan, Yunda

    2016-06-01

    An exact analytical solution is presented for the effective dynamic transverse shear modulus in a heterogeneous fluid-filled porous solid containing cylindrical inclusions. The complex and frequency-dependent properties of the dynamic shear modulus are caused by the physical mechanism of mesoscopic-scale wave-induced fluid flow whose scale is smaller than wavelength but larger than the size of pores. Our model consists of three phases: a long cylindrical inclusion, a cylindrical shell of poroelastic matrix material with different mechanical and/or hydraulic properties than the inclusion and an outer region of effective homogeneous medium of laterally infinite extent. The behavior of both the inclusion and the matrix is described by Biot's consolidation equations, whereas the surrounding effective medium which is used to describe the effective transverse shear properties of the inner poroelastic composite is assumed to be a viscoelastic solid whose complex transverse shear modulus needs to be determined. The determined effective transverse shear modulus is used to quantify the S-wave attenuation and velocity dispersion in heterogeneous fluid-filled poroelastic rocks. The calculation shows the relaxation frequency and relative position of various fluid saturation dispersion curves predicted by this study exhibit very good agreement with those of a previous two-dimensional finite-element simulation. For the double-porosity model (inclusions having a different solid frame than the matrix but the same pore fluid as the matrix) the effective shear modulus also exhibits a size-dependent characteristic that the relaxation frequency moves to lower frequencies by two orders of magnitude if the radius of the cylindrical poroelastic composite increases by one order of magnitude. For the patchy-saturation model (inclusions having the same solid frame as the matrix but with a different pore fluid from the matrix), the heterogeneity in pore fluid cannot cause any attenuation in

  7. Numerical treatment of two-phase flow in capillary heterogeneous porous media by finite-volume approximations

    OpenAIRE

    Evje, Steinar; Friis, Helmer André

    2012-01-01

    This paper examines two-phase flow in porous media with heterogeneous capillary pressure functions. This problem has received very little attention in the literature, and constitutes a challenge for numerical discretization, since saturation discontinuities arise at the interface between the different homogeneous regions in the domain. As a motivation we first consider a one-dimensional model problem, for which a semi-analytical solution is known, and examine some different fin...

  8. Effect of Pore-Scale Heterogeneity and Capillary-Viscous Fingering on Commingled Waterflood Oil Recovery in Stratified Porous Media

    OpenAIRE

    Al-Shalabi, Emad W.; Ghosh, B

    2016-01-01

    Oil recovery prediction and field pilot implements require basic understanding and estimation of displacement efficiency. Corefloods and glass micromodels are two of the commonly used experimental methods to achieve this. In this paper, waterflood recovery is investigated using layered etched glass micromodel and Berea sandstone core plugs with large permeability contrasts. This study focuses mainly on the effect of permeability (heterogeneity) in stratified porous media with no cross-flow. T...

  9. On the interpretation of double-packer tests in heterogeneous porous media: Numerical simulations using the stochastic continuum analogue

    International Nuclear Information System (INIS)

    Flow in fractured crystalline (hard) rocks is of interest in Sweden for assessing the postclosure radiological safety of a deep repository for high-level nuclear waste. For simulation of flow and mass transport in the far field different porous media concepts are often used, whereas discrete fracture/channel network concepts are often used for near-field simulations. Due to lack of data, it is generally necessary to have resort to single-hole double-packer test data for the far-field simulations, i.e., test data on a small scale are regularized in order to fit a comparatively coarser numerical discretization, which is governed by various computational constraints. In the present study the Monte Carlo method is used to investigate the relationship between the transmissivity value interpreted and the corresponding radius of influence in conjunction with single-hole double-packer tests in heterogeneous formations. The numerical flow domain is treated as a two-dimensional heterogeneous porous medium with a spatially varying diffusivity on 3 m scale. The Monte Carlo simulations demonstrate the sensitivity to the correlation range of a spatially varying diffusivity field. In contradiction to what is tacitly assumed in stochastic subsurface hydrology, the results show that the lateral support scale (e.g., the radius of influence) of transmissivity measurements in heterogeneous porous media is a random variable, which is affected by both the hydraulic and statistical characteristics. If these results are general, the traditional methods for scaling-up, assuming a constant lateral scale of support and a multi normal distribution, may lead to an underestimation of the persistence and connectivity of transmissive zones, particularly in highly heterogeneous porous media

  10. Numerical research on the anisotropic transport of thermal neutron in heterogeneous porous media with micron X-ray computed tomography

    OpenAIRE

    Yong Wang; Wenzheng Yue; Mo Zhang

    2016-01-01

    The anisotropic transport of thermal neutron in heterogeneous porous media is of great research interests in many fields. In this paper, it is the first time that a new model based on micron X-ray computed tomography (CT) has been proposed to simultaneously consider both the separation of matrix and pore and the distribution of mineral components. We apply the Monte Carlo method to simulate thermal neutrons transporting through the model along different directions, and meanwhile detect those ...

  11. Micro-PIV measurements of multiphase flow of water and supercritical CO2 in 2D heterogeneous porous micromodels

    Science.gov (United States)

    Li, Y.; Kazemifar, F.; Blois, G.; Christensen, K. T.

    2015-12-01

    Multiphase flow of water and supercritical carbon dioxide (CO2) in porous media is central to geological sequestration of CO2 into saline aquifers. However, our fundamental understanding of the coupled flow dynamics of CO2 and water in complex geologic media still remains limited, especially at the pore scale. Recently, studies have been carried out in 2D homogeneous models with the micro-PIV technique, yielding very interesting observations of pore-scale flow transport. The primary aim of this work is to leverage this experimental protocol to quantify the pore-scale flow of water and liquid/supercritical CO2 in 2D heterogeneous porous micromodels under reservoir-relevant conditions. The goal is to capture the dynamics of this multi-phase flow in a porous matrix that mimics the heterogeneity of natural rock. Fluorescent microscopy and the micro-PIV technique are employed to simultaneously measure the spatially-resolved instantaneous velocity field in the water and quantify the instantaneous spatial configuration of both phases. The results for heterogeneous micromodels will be presented and compared with those for homogeneous micromodels, yielding valuable insight into flow processes at the pore scale in natural rock.

  12. Streamline Simulation of a Two-Phase Flow in Heterogeneous and Anisotropic Porous Media

    Science.gov (United States)

    Cervantes, D.; Salazar, A.; de la Cruz, L.

    2013-05-01

    numerical errors on the solution. The domain of study is a heterogeneous and anisotropic porous media, with several distributions of injector and producer wells. [1] Muskat, M. and Wyckoff, R.: "Theoretical Analysis of Waterfooding Networks," Trans. AIME (1934) 107, 62-77.

  13. An efficient distribution method for nonlinear transport problems in highly heterogeneous stochastic porous media

    Science.gov (United States)

    Ibrahima, Fayadhoi; Meyer, Daniel; Tchelepi, Hamdi

    2016-04-01

    Because geophysical data are inexorably sparse and incomplete, stochastic treatments of simulated responses are crucial to explore possible scenarios and assess risks in subsurface problems. In particular, nonlinear two-phase flows in porous media are essential, yet challenging, in reservoir simulation and hydrology. Adding highly heterogeneous and uncertain input, such as the permeability and porosity fields, transforms the estimation of the flow response into a tough stochastic problem for which computationally expensive Monte Carlo (MC) simulations remain the preferred option.We propose an alternative approach to evaluate the probability distribution of the (water) saturation for the stochastic Buckley-Leverett problem when the probability distributions of the permeability and porosity fields are available. We give a computationally efficient and numerically accurate method to estimate the one-point probability density (PDF) and cumulative distribution functions (CDF) of the (water) saturation. The distribution method draws inspiration from a Lagrangian approach of the stochastic transport problem and expresses the saturation PDF and CDF essentially in terms of a deterministic mapping and the distribution and statistics of scalar random fields. In a large class of applications these random fields can be estimated at low computational costs (few MC runs), thus making the distribution method attractive. Even though the method relies on a key assumption of fixed streamlines, we show that it performs well for high input variances, which is the case of interest. Once the saturation distribution is determined, any one-point statistics thereof can be obtained, especially the saturation average and standard deviation. Moreover, the probability of rare events and saturation quantiles (e.g. P10, P50 and P90) can be efficiently derived from the distribution method. These statistics can then be used for risk assessment, as well as data assimilation and uncertainty reduction

  14. Online Adaptive Local-Global Model Reduction for Flows in Heterogeneous Porous Media

    KAUST Repository

    Efendiev, Yalchin

    2016-06-07

    We propose an online adaptive local-global POD-DEIM model reduction method for flows in heterogeneous porous media. The main idea of the proposed method is to use local online indicators to decide on the global update, which is performed via reduced cost local multiscale basis functions. This unique local-global online combination allows (1) developing local indicators that are used for both local and global updates (2) computing global online modes via local multiscale basis functions. The multiscale basis functions consist of offline and some online local basis functions. The approach used for constructing a global reduced system is based on Proper Orthogonal Decomposition (POD) Galerkin projection. The nonlinearities are approximated by the Discrete Empirical Interpolation Method (DEIM). The online adaption is performed by incorporating new data, which become available at the online stage. Once the criterion for updates is satisfied, we adapt the reduced system online by changing the POD subspace and the DEIM approximation of the nonlinear functions. The main contribution of the paper is that the criterion for adaption and the construction of the global online modes are based on local error indicators and local multiscale basis function which can be cheaply computed. Since the adaption is performed infrequently, the new methodology does not add significant computational overhead associated with when and how to adapt the reduced basis. Our approach is particularly useful for situations where it is desired to solve the reduced system for inputs or controls that result in a solution outside the span of the snapshots generated in the offline stage. Our method also offers an alternative of constructing a robust reduced system even if a potential initial poor choice of snapshots is used. Applications to single-phase and two-phase flow problems demonstrate the efficiency of our method.

  15. Heterogeneous photocatalysis of moxifloxacin in water: chemical transformation and ecotoxicity.

    Science.gov (United States)

    Van Doorslaer, Xander; Haylamicheal, Israel Deneke; Dewulf, Jo; Van Langenhove, Herman; Janssen, Colin R; Demeestere, Kristof

    2015-01-01

    This work provides new insights on the impact of TiO2/UV catalyzed chemical transformation of moxifloxacin on ecotoxicity effects towards the green alga Pseudokirchneriella subcapitata. The moxifloxacin median effect concentration (EC-50=0.78 [0.56, 1.09] mg L(-1)), determined in accordance to the OECD 72-h growth inhibition test guideline, was 7 times lower than that of the older and widely used fluoroquinolone ciprofloxacin (EC-50=5.57 [4.86, 6.38] mg L(-1)). Applying heterogeneous photocatalysis as an advanced oxidation technique to degrade moxifloxacin in aqueous solution decreased the average growth inhibition from 72% to 14% after 150 min of treatment. No significant carbon mineralization was observed and liquid chromatography mass spectrometry analysis revealed the formation of 13 degradation products for which a chemical structure could be proposed based on accurate mass determination. Combined chemical and ecotoxicological analysis showed that as long as moxifloxacin is present in the reaction solution, it is the main compound affecting algal growth inhibition. However, also the contribution of the degradation products to the observed ecotoxicity cannot be neglected. Photocatalytically induced modifications of moxifloxacin mainly occur at the diazobicyclo-substituent as ring opening, oxidation into carbonyl groups, and hydroxylation. This results into the formation of more hydrophilic compounds with a decreased biological activity compared with moxifloxacin. The change in lipophilicity, and possibly a modified acid-base speciation, most probably also affect the cell membrane permeation of the degradation products, which might be another factor explaining the observed lower residual ecotoxicity of the photocatalytically treated reaction solutions. PMID:24735961

  16. Elaboration of composite and chemically heterogeneous icephobic coatings

    Science.gov (United States)

    Arianpour, Faranak

    Atmospheric icing happens when the surfaces of exposed structures are subjected to contact with super-cooled water droplets or snow particles. Ice build-up on overhead transmission and distribution lines may lead to mechanical failure or insulator flashover, sometimes resulting in power outages with major socioeconomic consequences. The present study focused on the preparation of heterogeneous coatings (HCs) with hydro- and icephobic properties presenting a number of advantages, such as easy application, time-saving and low cost. The homo- and HCs were prepared by using different methods such as self-assembly, nanoparticles-based and Plasma-based techniques. Super-hydrophobic coatings with very low wetting hysteresis are also considered to be icephobic. However, even super-hydrophobic coatings can deteriorate during successive icing/de-icing cycles, and this can lead to ice mechanical anchoring since liquid water penetrates the porous surface. Additionally, the cost and complexity involved in the fabrication of such coatings as micro and nano roughness is created, constitute other hurdles. In this study HCs are considered as a coating including hydrocarbons and fluorocarbons, while purely hydrocarbons or fluorocarbons coatings are considered as the homogeneous coatings. It was shown by applying different functions (both C-F and C-H) the surface energy is decreased more compared to applying only one function (C-F or C-H alone). It should be noted that the water molecule orientations at the surfaces of the fluorocarbon and hydrocarbon groups were completely different. As a result, by inducing or creating various disparities (hydrocarbons and fluorocarbons) in terms of energy bonding, and water molecule orientation at the molecular level, the ice-solid interface is weakened. The wettability measurement of the HCs showed higher water contact angle (CA) values and smaller water contact angle hysteresis (CAH) values compared to homogeneous coatings. The most important

  17. Chemical placement in heterogeneous and long reach horizontal wells

    Energy Technology Data Exchange (ETDEWEB)

    Stalker, Robert; Wahid, Fazrie; Graham, Gordon M.

    2006-03-15

    The effective placement of chemical squeeze treatments in heterogeneous wells and long reach horizontal wells has proved a significant challenge, with various factors including heterogeneity, crossflow and pressure gradients between otherwise non-communicating zones within the well, all contributing to an uneven placement of the scale squeeze treatment into the reservoir. Current methods to circumvent these problems often rely on extremely expensive coiled tubing operations, staged diversion (temporary shut off) treatments or by designing treatments to deliberately overdose some zones in order to gain placement in other (e.g. low permeability) zones. Moreover for deepwater sub sea horizontal wells the costs associated with ''spot'' treating along the length of horizontal wells by coil tubing tractor operations can often be prohibitively expensive. For other very near well bore treatments such as acid stimulation a number of self diverting strategies including gelled acid treatments, staged viscoelastic surfactant treatments and foams have been applied in field treatments with some success. However the properties which make such treatments applicable for acid stimulation may also make them inappropriate for bullhead scale squeeze treatments. Recent work by the current authors has however indicated the possible benefits of using modified injection fluids to aid uniform scale inhibitor placement in such wells in order to effect more even placement. In summary this paper will describe the various options available for achieving self diversion and describes the potential drawbacks associated with the viscous placement fluids commonly used for acid simulation techniques. In addition, various simulation packages commonly used for scale related calculations are reviewed and their limitations, primarily due to the inherent assumptions made and input parameters used, for modelling squeeze treatments using such modified fluids are described. The paper

  18. Gravity-Driven Flow of non-Newtonian Fluids in Heterogeneous Porous Media: a Theoretical and Experimental Analysis

    Science.gov (United States)

    Di Federico, V.; Longo, S.; Ciriello, V.; Chiapponi, L.

    2015-12-01

    A theoretical and experimental analysis of non-Newtonian gravity-driven flow in porous media with spatially variable properties is presented. The motivation for our study is the rheological complexity exhibited by several environmental contaminants (wastewater sludge, oil pollutants, waste produced by the minerals and coal industries) and remediation agents (suspensions employed to enhance the efficiency of in-situ remediation). Natural porous media are inherently heterogeneous, and this heterogeneity influences the extent and shape of the porous domain invaded by the contaminant or remediation agent. To grasp the combined effect of rheology and spatial heterogeneity, we consider: a) the release of a thin current of non-Newtonian power-law fluid into a 2-D, semi-infinite and saturated porous medium above a horizontal bed; b) perfectly stratified media, with permeability and porosity varying along the direction transverse (vertical) or parallel (horizontal) to the flow direction. This continuous variation of spatial properties is described by two additional parameters. In order to represent several possible spreading scenarios, we consider: i) instantaneous injection with constant mass; ii) continuous injection with time-variable mass; iii) instantaneous release of a mound of fluid, which can drain freely out of the formation at the origin (dipole flow). Under these assumptions, scalings for current length and thickness are derived in self similar form. An analysis of the conditions on model parameters required to avoid an unphysical or asymptotically invalid result is presented. Theoretical results are validated against multiple sets of experiments, conducted for different combinations of spreading scenarios and types of stratification. Two basic setups are employed for the experiments: I) direct flow simulation in an artificial porous medium constructed superimposing layers of glass beads of different diameter; II) a Hele-Shaw (HS) analogue made of two parallel

  19. Theory of water desalination by porous electrodes with fixed chemical charge

    OpenAIRE

    Biesheuvel, P. M.; Suss, M. E.; Hamelers, H.V.M.

    2015-01-01

    Water desalination by capacitive deionization (CDI) is performed via electrochemical cells consisting of two porous carbon electrodes. Upon transferring charge from one electrode to the other, ions are removed from the feedwater by electrosorption into electrical double layers (EDLs) within the micropores of the porous carbon. When using electrodes containing fixed chemical charge in the micropores, various counterintuitive observations have been made, such as "inverted CDI" where upon chargi...

  20. Recognition and repair of chemically heterogeneous structures at DNA ends.

    Science.gov (United States)

    Andres, Sara N; Schellenberg, Matthew J; Wallace, Bret D; Tumbale, Percy; Williams, R Scott

    2015-01-01

    Exposure to environmental toxicants and stressors, radiation, pharmaceutical drugs, inflammation, cellular respiration, and routine DNA metabolism all lead to the production of cytotoxic DNA strand breaks. Akin to splintered wood, DNA breaks are not "clean." Rather, DNA breaks typically lack DNA 5'-phosphate and 3'-hydroxyl moieties required for DNA synthesis and DNA ligation. Failure to resolve damage at DNA ends can lead to abnormal DNA replication and repair, and is associated with genomic instability, mutagenesis, neurological disease, ageing and carcinogenesis. An array of chemically heterogeneous DNA termini arises from spontaneously generated DNA single-strand and double-strand breaks (SSBs and DSBs), and also from normal and/or inappropriate DNA metabolism by DNA polymerases, DNA ligases and topoisomerases. As a front line of defense to these genotoxic insults, eukaryotic cells have accrued an arsenal of enzymatic first responders that bind and protect damaged DNA termini, and enzymatically tailor DNA ends for DNA repair synthesis and ligation. These nucleic acid transactions employ direct damage reversal enzymes including Aprataxin (APTX), Polynucleotide kinase phosphatase (PNK), the tyrosyl DNA phosphodiesterases (TDP1 and TDP2), the Ku70/80 complex and DNA polymerase β (POLβ). Nucleolytic processing enzymes such as the MRE11/RAD50/NBS1/CtIP complex, Flap endonuclease (FEN1) and the apurinic endonucleases (APE1 and APE2) also act in the chemical "cleansing" of DNA breaks to prevent genomic instability and disease, and promote progression of DNA- and RNA-DNA damage response (DDR and RDDR) pathways. Here, we provide an overview of cellular first responders dedicated to the detection and repair of abnormal DNA termini. PMID:25111769

  1. Variations in hydraulic conductivity with scale of measurement during aquifer tests in heterogeneous, porous carbonate rocks

    Science.gov (United States)

    Schulze-Makuch, Dirk; Cherkauer, Douglas S.

    Previous studies have shown that hydraulic conductivity of an aquifer seems to increase as the portion of the aquifer tested increases. To date, such studies have all relied on different methods to determine hydraulic conductivity at each scale of interest, which raises the possibility that the observed increase in hydraulic conductivity is due to the measurement method, not to the scale. This study analyzes hydraulic conductivity with respect to scale during individual aquifer tests in porous, heterogeneous carbonate rocks in southeastern Wisconsin, USA. Results from this study indicate that hydraulic conductivity generally increases during an individual test as the volume of aquifer impacted increases, and the rate of this increase is the same as the rate of increase determined by using different measurement methods. Thus, scale dependence of hydraulic conductivity during single tests does not depend on the method of measurement. This conclusion is supported by 22 of 26 aquifer tests conducted in porous-flow-dominated carbonate units within the aquifer. Instead, scale dependency is probably caused by heterogeneities within the aquifer, a conclusion supported by digital simulation. All of the observed types of hydraulic-conductivity variations with scale during individual aquifer tests can be explained by a conceptual model of a simple heterogeneous aquifer composed of high-conductivity zones within a low-conductivity matrix. Résumé Certaines études ont montré que la conductivité hydraulique d'un aquifère semble augmenter en même temps que la partie testée de l'aquifère s'étend. Jusqu'à présent, ces études ont toutes reposé sur des méthodes de détermination de la conductivité hydraulique différentes pour chaque niveau d'échelle, ce qui a conduit à penser que l'augmentation observée de la conductivité hydraulique pouvait être due aux méthodes de mesure et non à l'effet d'échelle. Cette étude analyse la conductivité hydraulique par

  2. Finite volume approximation of the three-dimensional flow equation in axisymmetric, heterogeneous porous media based on local analytical solution

    KAUST Repository

    Salama, Amgad

    2013-09-01

    In this work the problem of flow in three-dimensional, axisymmetric, heterogeneous porous medium domain is investigated numerically. For this system, it is natural to use cylindrical coordinate system, which is useful in describing phenomena that have some rotational symmetry about the longitudinal axis. This can happen in porous media, for example, in the vicinity of production/injection wells. The basic feature of this system is the fact that the flux component (volume flow rate per unit area) in the radial direction is changing because of the continuous change of the area. In this case, variables change rapidly closer to the axis of symmetry and this requires the mesh to be denser. In this work, we generalize a methodology that allows coarser mesh to be used and yet yields accurate results. This method is based on constructing local analytical solution in each cell in the radial direction and moves the derivatives in the other directions to the source term. A new expression for the harmonic mean of the hydraulic conductivity in the radial direction is developed. Apparently, this approach conforms to the analytical solution for uni-directional flows in radial direction in homogeneous porous media. For the case when the porous medium is heterogeneous or the boundary conditions is more complex, comparing with the mesh-independent solution, this approach requires only coarser mesh to arrive at this solution while the traditional methods require more denser mesh. Comparisons for different hydraulic conductivity scenarios and boundary conditions have also been introduced. © 2013 Elsevier B.V.

  3. Hybrid finite volume scheme for a two-phase flow in heterogeneous porous media*

    Directory of Open Access Journals (Sweden)

    Brenner Konstantin

    2012-04-01

    Full Text Available We propose a finite volume method on general meshes for the numerical simulation of an incompressible and immiscible two-phase flow in porous media. We consider the case that can be written as a coupled system involving a degenerate parabolic convection-diffusion equation for the saturation together with a uniformly elliptic equation for the global pressure. The numerical scheme, which is implicit in time, allows computations in the case of a heterogeneous and anisotropic permeability tensor. The convective fluxes, which are non monotone with respect to the unknown saturation and discontinuous with respect to the space variables, are discretized by means of a special Godunov scheme. We prove the existence of a discrete solution which converges, along a subsequence, to a solution of the continuous problem. We present a number of numerical results in space dimension two, which confirm the efficiency of the numerical method. Nous proposons un schéma de volumes finis hybrides pour la discrétisation d’un problème d’écoulement diphasique incompressible et immiscible en milieu poreux. On suppose que ce problème a la forme d’une équation parabolique dégénérée de convection-diffusion en saturation couplée à une équation uniformément elliptique en pression. On considère un schéma implicite en temps, où les flux diffusifs sont discrétisés par la méthode des volumes finis hybride, ce qui permet de pouvoir traiter le cas d’un tenseur de perméabilité anisotrope et hétérogène sur un maillage très général, et l’on s’appuie sur un schéma de Godunov pour la discrétisation des flux convectifs, qui peuvent être non monotones et discontinus par rapport aux variables spatiales. On démontre l’existence d’une solution discrète, dont une sous-suite converge vers une solution faible du problème continu. On présente finalement des cas test bidimensionnels.

  4. The use of laboratory experiments for the study of conservative solute transport in heterogeneous porous media

    Science.gov (United States)

    Silliman, S. E.; Zheng, L.; Conwell, P.

    Laboratory experiments on heterogeneous porous media (otherwise known as intermediate scale experiments, or ISEs) have been increasingly relied upon by hydrogeologists for the study of saturated and unsaturated groundwater systems. Among the many ongoing applications of ISEs is the study of fluid flow and the transport of conservative solutes in correlated permeability fields. Recent advances in ISE design have provided the capability of creating correlated permeability fields in the laboratory. This capability is important in the application of ISEs for the assessment of recent stochastic theories. In addition, pressure-transducer technology and visualization methods have provided the potential for ISEs to be used in characterizing the spatial distributions of both hydraulic head and local water velocity within correlated permeability fields. Finally, various methods are available for characterizing temporal variations in the spatial distribution (and, thereby, the spatial moments) of solute concentrations within ISEs. It is concluded, therefore, that recent developments in experimental techniques have provided an opportunity to use ISEs as important tools in the continuing study of fluid flow and the transport of conservative solutes in heterogeneous, saturated porous media. Résumé Les hydrogéologues se sont progressivement appuyés sur des expériences de laboratoire sur des milieux poreux hétérogènes (connus aussi par l'expression "Expériences àéchelle intermédiaire", ISE) pour étudier les zones saturées et non saturées des aquifères. Parmi les nombreuses applications en cours des ISE, il faut noter l'étude de l'écoulement de fluide et le transport de solutés conservatifs dans des champs aux perméabilités corrélées. Les récents progrès du protocole des ISE ont donné la possibilité de créer des champs de perméabilités corrélées au laboratoire. Cette possibilité est importante dans l'application des ISE pour l'évaluation des th

  5. The effect of entrapped nonaqueous phase liquids on tracer transport in heterogeneous porous media: Laboratory experiments at the intermediate scale

    Science.gov (United States)

    Barth, G.R.; Illangasekare, T.H.; Rajaram, H.

    2003-01-01

    This work considers the applicability of conservative tracers for detecting high-saturation nonaqueous-phase liquid (NAPL) entrapment in heterogeneous systems. For this purpose, a series of experiments and simulations was performed using a two-dimensional heterogeneous system (10??1.2 m), which represents an intermediate scale between laboratory and field scales. Tracer tests performed prior to injecting the NAPL provide the baseline response of the heterogeneous porous medium. Two NAPL spill experiments were performed and the entrapped-NAPL saturation distribution measured in detail using a gamma-ray attenuation system. Tracer tests following each of the NAPL spills produced breakthrough curves (BTCs) reflecting the impact of entrapped NAPL on conservative transport. To evaluate significance, the impact of NAPL entrapment on the conservative-tracer breakthrough curves was compared to simulated breakthrough curve variability for different realizations of the heterogeneous distribution. Analysis of the results reveals that the NAPL entrapment has a significant impact on the temporal moments of conservative-tracer breakthrough curves. ?? 2003 Elsevier B.V. All rights reserved.

  6. A note on variational multiscale methods for high-contrast heterogeneous porous media flows with rough source terms

    KAUST Repository

    Calo, Victor M.

    2011-09-01

    In this short note, we discuss variational multiscale methods for solving porous media flows in high-contrast heterogeneous media with rough source terms. Our objective is to separate, as much as possible, subgrid effects induced by the media properties from those due to heterogeneous source terms. For this reason, enriched coarse spaces designed for high-contrast multiscale problems are used to represent the effects of heterogeneities of the media. Furthermore, rough source terms are captured via auxiliary correction equations that appear in the formulation of variational multiscale methods [23]. These auxiliary equations are localized and one can use additive or multiplicative constructions for the subgrid corrections as discussed in the current paper. Our preliminary numerical results show that one can capture the effects due to both spatial heterogeneities in the coefficients (such as permeability field) and source terms (e.g., due to singular well terms) in one iteration. We test the cases for both smooth source terms and rough source terms and show that with the multiplicative correction, the numerical approximations are more accurate compared to the additive correction. © 2010 Elsevier Ltd.

  7. Gravity-destabilized nonwetting phase invasion in macro-heterogeneous porous media: Experimental observations of invasion dynamics and scale analysis

    Energy Technology Data Exchange (ETDEWEB)

    GLASS JR.,ROBERT J.; CONRAD,STEPHEN H.; PEPLINSKI,WILLIAM J.

    1999-02-16

    The authors designed and conducted experiments in a heterogeneous sand pack where gravity-destabilized nonwetting phase invasion (CO{sub 2} and TCE) could be recorded using high resolution light transmission methods. The heterogeneity structure was designed to be reminiscent of fluvial channel lag cut-and-fill architecture and contain a series of capillary barriers. As invasion progressed, nonwetting phase structure developed a series of fingers and pools; behind the growing front they found nonwetting phase saturation to pulsate in certain regions when viscous forces were low. Through a scale analysis, they derive a series of length scales that describe finger diameter, pool height and width, and regions where pulsation occurs within a heterogeneous porous medium. In all cases, they find that the intrinsic pore scale nature of the invasion process and resulting structure must be incorporated into the analysis to explain experimental results. The authors propose a simple macro-scale structural growth model that assembles length scales for sub-structures to delineate nonwetting phase migration from a source into a heterogeneous domain. For such a model applied at the field scale for DNAPL migration, they expect capillary and gravity forces within the complex subsurface lithology to play the primary roles with viscous forces forming a perturbation on the inviscid phase structure.

  8. Multi-rate mass transfer modeling of two-phase flow in highly heterogeneous fractured and porous media

    Science.gov (United States)

    Tecklenburg, Jan; Neuweiler, Insa; Carrera, Jesus; Dentz, Marco

    2016-05-01

    We study modeling of two-phase flow in highly heterogeneous fractured and porous media. The flow behaviour is strongly influenced by mass transfer between a highly permeable (mobile) fracture domain and less permeable (immobile) matrix blocks. We quantify the effective two-phase flow behavior using a multirate rate mass transfer (MRMT) approach. We discuss the range of applicability of the MRMT approach in terms of the pertinent viscous and capillary diffusion time scales. We scrutinize the linearization of capillary diffusion in the immobile regions, which allows for the formulation of MRMT in the form of a non-local single equation model. The global memory function, which encodes mass transfer between the mobile and the immobile regions, is at the center of this method. We propose two methods to estimate the global memory function for a fracture network with given fracture and matrix geometry. Both employ a scaling approach based on the known local memory function for a given immobile region. With the first method, the local memory function is calculated numerically, while the second one employs a parametric memory function in form of truncated power-law. The developed concepts are applied and tested for fracture networks of different complexity. We find that both physically based parameter estimation methods for the global memory function provide predictive MRMT approaches for the description of multiphase flow in highly heterogeneous porous media.

  9. Eulerian Lagrangian Adaptive Fup Collocation Method for solving the conservative solute transport in heterogeneous porous media

    Science.gov (United States)

    Gotovac, Hrvoje; Srzic, Veljko

    2014-05-01

    linear system on adaptive grid because each Fup coefficient is obtained by predefined formulas equalizing Fup expansion around corresponding collocation point and particular collocation operator based on few surrounding solution values. Furthermore, each Fup coefficient can be obtained independently which is perfectly suited for parallel processing. Adaptive grid in each time step is obtained from solution of the last time step or initial conditions and advective Lagrangian step in the current time step according to the velocity field and continuous streamlines. On the other side, we implement explicit stabilized routine SERK2 for dispersive Eulerian part of solution in the current time step on obtained spatial adaptive grid. Overall adaptive concept does not require the solving of large linear systems for the spatial and temporal approximation of conservative transport. Also, this new Eulerian-Lagrangian-Collocation scheme resolves all mentioned numerical problems due to its adaptive nature and ability to control numerical errors in space and time. Proposed method solves advection in Lagrangian way eliminating problems in Eulerian methods, while optimal collocation grid efficiently describes solution and boundary conditions eliminating usage of large number of particles and other problems in Lagrangian methods. Finally, numerical tests show that this approach enables not only accurate velocity field, but also conservative transport even in highly heterogeneous porous media resolving all spatial and temporal scales of concentration field.

  10. Stability analysis of non-inertial thin film flow over a heterogeneously heated porous substrate

    Science.gov (United States)

    Kumawat, Tara Chand; Tiwari, Naveen

    2016-02-01

    The dynamics and linear stability of a gravity drive thin film flowing over non-uniformly heated porous substrate are studied. A governing equation for the evolution of film-thickness is derived within the lubrication approximation. Darcy-Brinkman equation is used to model flow in the porous medium along with a tangential stress-jump condition at the interface of the porous layer and the fluid film. A temperature profile is imposed at the solid wall to model an embedded heater beneath the porous layer. At the upstream edge of the heater, an opposing thermocapillary stress at the liquid-air interface leads to the formation of a thermocapillary ridge. The ridge becomes unstable beyond a critical Marangoni number leading to the formation of rivulets that are periodic in the spanwise direction. Increase in the values of parameters such as Darcy number, stress jump coefficient, and porosity is shown to have stabilizing effect on the film dynamics. The critical Marangoni number is shown to increase monotonically with Darcy number for various values of porosity. At large values of stress-jump coefficient, a non-monotonic variation in critical Marangoni number versus Darcy number is shown. A correlation is developed numerically for the ratio of critical Marangoni number at large Darcy number to that for a non-porous substrate as a function of porosity and thickness of the porous substrate. A transient growth analysis is carried out followed by non-linear stability analysis. The non-modal growth is found to be negligible thus indicating that the eigenvalues are physically determinant.

  11. Biomimetic Deposition of Apatite on Surface Chemically Modified Porous NiTi Shapememory Alloy

    Science.gov (United States)

    Wu, S. L.; Liu, X. M.; Chung, C. Y.; Chu, Paul K.; Chan, Y. L.; Yeung, K. W. K.; Chu, C. L.

    Porous NiTi shape memory alloy (SMA) with 48% porosity and an average pore size of 50-800 μm was synthesized by capsule-free hot isostatic pressing (CF-HIP). To enhance the surface bioactivity, the porous NiTi SMA was subjected to H2O2 and subsequent NaOH treatment. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses revealed that a porous sodium titanate (Na2TiO3) film had formed on the surface of the porous NiTi SMA. An apatite layer was deposited on this film after immersion in simulated body fluid at 37°C, while no apatite could be found on the surface of the untreated porous NiTi SMA. The formation of the apatite layer infers that the bioactivity of the porous NiTi SMA may be enhanced by surface chemical treatment, which is favorable for its application as bone implants.

  12. Theory of Water Desalination by Porous Electrodes with Immobile Chemical Charge

    NARCIS (Netherlands)

    Biesheuvel, P.M.; Hamelers, H.V.M.; Suss, M.E.

    2015-01-01

    In capacitive deionization (CDI), water is desalinated by storing ions in electrical double layers (EDLs) within the micropores of charged porous carbon electrodes. Recent experiments using chemically modified electrodes have shown differing, novel phenomena such as "inverted CDI," "enhanced CDI,

  13. Porous chitosan scaffold cross-linked by chemical and natural procedure applied to investigate cell regeneration

    International Nuclear Information System (INIS)

    Highlights: ► Polymeric scaffolds, made from chitosan-based films fixed by chemical (citrate) or natural method (genipin), were developed. ► Nano-indentation with a constant harmonic frequency was applied on porous scaffolds to explore their surface mechanics. ► The relationship between surface mechanical property and cell-surface interactions of scaffold materials was demonstrated. ► Porous scaffolds cross-linked by genipin showed adequate cell affinity, non-toxicity, and suitable mechanical properties. - Abstract: Porous chitosan scaffold is used for tissue engineering and drug delivery, but is limited as a scaffold material due to its mechanical weakness, which restrains cell adhesion on the surface. In this study, a chemical reagent (citrate) and a natural reagent (genipin) are used as cross-linkers for the formation of chitosan-based films. Nanoindentation technique with a continuous stiffness measurement system is particularly applied on the porous scaffold surface to examine the characteristic modulus and nanohardness of a porous scaffold surface. The characteristic modulus of a genipin-cross-linked chitosan surface is ≈2.325 GPa, which is significantly higher than that of an uncross-linked one (≈1.292 GPa). The cell-scaffold surface interaction is assessed. The cell morphology and results of an MTS assay of 3T3-fibroblast cells of a genipin-cross-linked chitosan surface indicate that the enhancement of mechanical properties induced cell adhesion and proliferation on the modified porous scaffold surface. The pore size and mechanical properties of porous chitosan film can be tuned for specific applications such as tissue regeneration.

  14. Chemical treatments of the nanocrystalline porous TiO2 electrodes

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Two types of nanocrystalline porous TiO2 electrodes were prepared by the hydrothermal and painting methods. The incident photon-to-current efficiency and photoelectrical conversion efficiency were both improved by chemical treatments of titanium tetrachloride and titanium isopropoxide. The surface roughness, quantities of adsorbed dye, photocurrent-voltage curves, IR spectra and UV-visible absorption spectra were measured, and the mechanism of chemical treatments was discussed.

  15. Heterogeneously Catalysed Chemical Reactions in Carbon Dioxide Medium

    OpenAIRE

    Musko, Nikolai E.; Grumwaldt, Jan-Dierk; Jensen, Anker Degn; Kontogeorgis, Georgios

    2013-01-01

    I dette Ph.D.-studium blev de forskellige kemiteknikområder - heterogen katalyse, superkritiske væsker og faseligevægtstermodynamik bragt sammen for udvalgte reaktioner. For at udnytte de gavnlige egenskaber af superkritiske væsker i heterogen katalyse blev eksperimentelle studier af katalytiske kemiske reaktioner i tæt og superkritisk kuldioxid suppleret med teoretiske beregninger af faseligevægte ved hjælp af avancerede termodynamiske modeller.I de seneste år er bruget af komprimeret kuldio...

  16. Impact of supersonic and subsonic aircraft on ozone: Including heterogeneous chemical reaction mechanisms

    Science.gov (United States)

    Kinnison, Douglas E.; Wuebbles, Donald J.

    1994-01-01

    Preliminary calculations suggest that heterogeneous reactions are important in calculating the impact on ozone from emissions of trace gases from aircraft fleets. In this study, three heterogeneous chemical processes that occur on background sulfuric acid aerosols are included and their effects on O3, NO(x), Cl(x), HCl, N2O5, ClONO2 are calculated.

  17. Impact of supersonic and subsonic aircraft on ozone: Including heterogeneous chemical reaction mechanisms

    International Nuclear Information System (INIS)

    Preliminary calculations suggest that heterogeneous reactions are important in calculating the impact on ozone from emissions of trace gases from aircraft fleets. In this study, three heterogeneous chemical processes that occur on background sulfuric acid aerosols are included and their effects on O3, NOx, Clx, HCl, N2O5, ClONO2 are calculated

  18. Synthesis of sulfonated porous carbon nanospheres solid acid by a facile chemical activation route

    Energy Technology Data Exchange (ETDEWEB)

    Chang, Binbin, E-mail: changbinbin806@163.com; Guo, Yanzhen; Yin, Hang; Zhang, Shouren; Yang, Baocheng, E-mail: baochengyang@yahoo.com

    2015-01-15

    Generally, porous carbon nanospheres materials are usually prepared via a template method, which is a multi-steps and high-cost strategy. Here, we reported a porous carbon nanosphere solid acid with high surface area and superior porosity, as well as uniform nanospheical morphology, which prepared by a facile chemical activation with ZnCl{sub 2} using resorcinol-formaldehyde (RF) resins spheres as precursor. The activation of RF resins spheres by ZnCl{sub 2} at 400 °C brought high surface area and large volume, and simultaneously retained numerous oxygen-containing and hydrogen-containing groups due to the relatively low processing temperature. The presence of these functional groups is favorable for the modification of –SO{sub 3}H groups by a followed sulfonation treating with sulphuric acid and organic sulfonic acid. The results of N{sub 2} adsorption–desorption and electron microscopy clearly showed the preservation of porous structure and nanospherical morphology. Infrared spectra certified the variation of surface functional groups after activation and the successful modification of –SO{sub 3}H groups after sulfonation. The acidities of catalysts were estimated by an indirect titration method and the modified amount of –SO{sub 3}H groups were examined by energy dispersive spectra. The results suggested sulfonated porous carbon nanospheres catalysts possessed high acidities and –SO{sub 3}H densities, which endowed their significantly catalytic activities for biodiesel production. Furthermore, their excellent stability and recycling property were also demonstrated by five consecutive cycles. - Graphical abstract: Sulfonated porous carbon nanospheres with high surface area and superior catalytic performance were prepared by a facile chemical activation route. - Highlights: • Porous carbon spheres solid acid prepared by a facile chemical activation. • It owns high surface area, superior porosity and uniform spherical morphology. • It possesses

  19. Synthesis of sulfonated porous carbon nanospheres solid acid by a facile chemical activation route

    International Nuclear Information System (INIS)

    Generally, porous carbon nanospheres materials are usually prepared via a template method, which is a multi-steps and high-cost strategy. Here, we reported a porous carbon nanosphere solid acid with high surface area and superior porosity, as well as uniform nanospheical morphology, which prepared by a facile chemical activation with ZnCl2 using resorcinol-formaldehyde (RF) resins spheres as precursor. The activation of RF resins spheres by ZnCl2 at 400 °C brought high surface area and large volume, and simultaneously retained numerous oxygen-containing and hydrogen-containing groups due to the relatively low processing temperature. The presence of these functional groups is favorable for the modification of –SO3H groups by a followed sulfonation treating with sulphuric acid and organic sulfonic acid. The results of N2 adsorption–desorption and electron microscopy clearly showed the preservation of porous structure and nanospherical morphology. Infrared spectra certified the variation of surface functional groups after activation and the successful modification of –SO3H groups after sulfonation. The acidities of catalysts were estimated by an indirect titration method and the modified amount of –SO3H groups were examined by energy dispersive spectra. The results suggested sulfonated porous carbon nanospheres catalysts possessed high acidities and –SO3H densities, which endowed their significantly catalytic activities for biodiesel production. Furthermore, their excellent stability and recycling property were also demonstrated by five consecutive cycles. - Graphical abstract: Sulfonated porous carbon nanospheres with high surface area and superior catalytic performance were prepared by a facile chemical activation route. - Highlights: • Porous carbon spheres solid acid prepared by a facile chemical activation. • It owns high surface area, superior porosity and uniform spherical morphology. • It possesses high acidity and high –SO3H density. • It

  20. High-resolution Monte Carlo simulation of flow and conservative transport in heterogeneous porous media 2. Transport results

    Science.gov (United States)

    Naff, R.L.; Haley, D.F.; Sudicky, E.A.

    1998-01-01

    In this, the second of two papers concerned with the use of numerical simulation to examine flow and transport parameters in heterogeneous porous media via Monte Carlo methods, results from the transport aspect of these simulations are reported on. Transport simulations contained herein assume a finite pulse input of conservative tracer, and the numerical technique endeavors to realistically simulate tracer spreading as the cloud moves through a heterogeneous medium. Medium heterogeneity is limited to the hydraulic conductivity field, and generation of this field assumes that the hydraulic- conductivity process is second-order stationary. Methods of estimating cloud moments, and the interpretation of these moments, are discussed. Techniques for estimation of large-time macrodispersivities from cloud second-moment data, and for the approximation of the standard errors associated with these macrodispersivities, are also presented. These moment and macrodispersivity estimation techniques were applied to tracer clouds resulting from transport scenarios generated by specific Monte Carlo simulations. Where feasible, moments and macrodispersivities resulting from the Monte Carlo simulations are compared with first- and second-order perturbation analyses. Some limited results concerning the possible ergodic nature of these simulations, and the presence of non- Gaussian behavior of the mean cloud, are reported on as well.

  1. Generalized Lagrangian Coordinates for Transport and Two-Phase Flows in Heterogeneous Anisotropic Porous Media

    OpenAIRE

    Plouraboué, Franck; Bergeon, Alain; Azaïez, Mejdi

    2001-01-01

    We show how Lagrangian coordinates provide an effective representation of how difficult non-linear, hyperbolic transport problems in porous media can be dealt with. Recalling Lagrangian description first, we then derive some basic but remarkable properties useful for the numerical com- putation of projected transport operators. We furthermore introduce new generalized Lagrangian coordinates with their application to the Darcy–Muskat two-phase flow models. We show how these general...

  2. Heterogeneous nucleation of ice from supercooled NaCl solution confined in porous cement paste

    OpenAIRE

    Zeng, Qiang; Li, Kefei; FEN CHONG, Teddy

    2015-01-01

    Clarifying the nucleation process of chloride-based deicing salt solution (e.g., NaCl solution) confined in cement-based porous materials remains an important issue to understand its detrimental effects on material substrates. In this study, the pore structures of hardened cement pastes were characterized by mercury-intrusion and nitrogen-sorption porosimetry. The ice nucleation temperature of NaCl solution of different concentrations confined in the hardened cement pastes was measured and an...

  3. Multilevel Monte Carlo for two phase flow and Buckley–Leverett transport in random heterogeneous porous media

    International Nuclear Information System (INIS)

    Monte Carlo (MC) is a well known method for quantifying uncertainty arising for example in subsurface flow problems. Although robust and easy to implement, MC suffers from slow convergence. Extending MC by means of multigrid techniques yields the multilevel Monte Carlo (MLMC) method. MLMC has proven to greatly accelerate MC for several applications including stochastic ordinary differential equations in finance, elliptic stochastic partial differential equations and also hyperbolic problems. In this study, MLMC is combined with a streamline-based solver to assess uncertain two phase flow and Buckley–Leverett transport in random heterogeneous porous media. The performance of MLMC is compared to MC for a two dimensional reservoir with a multi-point Gaussian logarithmic permeability field. The influence of the variance and the correlation length of the logarithmic permeability on the MLMC performance is studied

  4. Effect of Pore-Scale Heterogeneity and Capillary-Viscous Fingering on Commingled Waterflood Oil Recovery in Stratified Porous Media

    Directory of Open Access Journals (Sweden)

    Emad W. Al-Shalabi

    2016-01-01

    Full Text Available Oil recovery prediction and field pilot implements require basic understanding and estimation of displacement efficiency. Corefloods and glass micromodels are two of the commonly used experimental methods to achieve this. In this paper, waterflood recovery is investigated using layered etched glass micromodel and Berea sandstone core plugs with large permeability contrasts. This study focuses mainly on the effect of permeability (heterogeneity in stratified porous media with no cross-flow. Three experimental setups were designed to represent uniformly stratified oil reservoir with vertical discontinuity in permeability. Waterflood recovery to residual oil saturation (Sor is measured through glass micromodel (to aid visual observation, linear coreflood, and forced drainage-imbibition processes by ultracentrifuge. Six oil samples of low-to-medium viscosity and porous media of widely different permeability (darcy and millidarcy ranges were chosen for the study. The results showed that waterflood displacement efficiencies are consistent in both permeability ranges, namely, glass micromodel and Berea sandstone core plugs. Interestingly, the experimental results show that the low permeability zones resulted in higher ultimate oil recovery compared to high permeability zones. At Sor microheterogeneity and fingering are attributed for this phenomenon. In light of the findings, conformance control is discussed for better sweep efficiency. This paper may be of help to field operators to gain more insight into microheterogeneity and fingering phenomena and their impact on waterflood recovery estimation.

  5. Heterogeneous Catalytic Conversion of Biobased Chemicals into Liquid Fuels in the Aqueous Phase.

    Science.gov (United States)

    Wu, Kejing; Wu, Yulong; Chen, Yu; Chen, Hao; Wang, Jianlong; Yang, Mingde

    2016-06-22

    Different biobased chemicals are produced during the conversion of biomass into fuels through various feasible technologies (e.g., hydrolysis, hydrothermal liquefaction, and pyrolysis). The challenge of transforming these biobased chemicals with high hydrophilicity is ascribed to the high water content of the feedstock and the inevitable formation of water. Therefore, aqueous-phase processing is an interesting technology for the heterogeneous catalytic conversion of biobased chemicals. Different reactions, such as dehydration, isomerization, aldol condensation, ketonization, and hydrogenation, are applied for the conversion of sugars, furfural/hydroxymethylfurfural, acids, phenolics, and so on over heterogeneous catalysts. The activity, stability, and reusability of the heterogeneous catalysts in water are summarized, and deactivation processes and several strategies are introduced to improve the stability of heterogeneous catalysts in the aqueous phase. PMID:27158985

  6. Upscaling of Heterogeneous Porous Rocks Using High Resolution Hydrogeophysical Scanning Measurements

    Science.gov (United States)

    Bussod, G. Y.; Svyatskiy, D.; Zyvoloski, G.; Boitnott, G. N.; Lichtner, P. C.; Moulton, J. D.

    2009-12-01

    This research is part of a DOE SBIR project that combines physical properties measurements on consolidated and unconsolidated subsurface lithologies, with numerical and effective media models that describe subsurface contaminant flow and transport. This paper presents results from an application of a new high-resolution methodology for the laboratory characterization of hydrogeophysical properties on core and field samples. The methodology is used to constrain contaminant flow and transport models for both unsaturated and saturated subsurface conditions. Spatially integrated fine-scale scanning (mm-cm resolution) of permeabilities, ultrasonic velocities and electrical conductivities on core and field samples are used to quantify heterogeneities at the smallest continuum scale. Through application of numerical and effective medium upscaling techniques, the scans provide a means to assign hydrogeophysical properties and model parameters at scales more appropriate to field applications, while preserving the physical influence of fine scale heterogeneities that cannot be explicitly modeled. The methodology is being applied to several contaminated DOE sites at LANL, NM, Hanford, WA and Rifle, CO. We illustrate that fine- and meso- scale heterogeneities (mm-m) can cause significant saturation dependent anisotropy in hydrogeophysical properties (e.g., electrical conductivity and relative permeability). These effects are captured in our upscaling methodology to provide more accurate model parameters used in representation of the contaminated subsurface. Through a series of examples, we show how quantification of the fine scale heterogeneities of a particular flow unit can be used to constrain upscaled model properties at the meter scale. We show that as a result of these heterogeneities, the change in scale from centimeters to meters requires a change in character of the capillary pressure / relative permeability relationships. As an example, we find that after applying

  7. Heterogeneous porous media permeability field characterization from fluid displacement data; Integration de donnees de deplacements de fluides dans la caracterisation de milieux poreux heterogenes

    Energy Technology Data Exchange (ETDEWEB)

    Kretz, V.

    2002-11-01

    The prediction of oil recovery or pollutant dispersion requires an accurate knowledge of the permeability field distribution. Available data are usually measurements in well bores, and, since a few years, 4D-seismic data (seismic mappings repeated in time). Such measurements allow to evaluate fluids displacements fronts evolution. The purpose of the thesis is to evaluate the possibility to determinate permeability fields from fluid displacement measurements in heterogeneous porous media. At the laboratory scale, experimental studies are made on a model and on numerical simulations. The system uses blocks of granular materials whose individual geometries and permeabilities are controlled. The fluids displacements are detected with an acoustical. The key parameters of the study are the size and spatial correlation of the permeability heterogeneity distribution, and the influence of viscosity and gravity contrasts between the injected ant displaced fluid. Then the inverse problem - evaluating the permeability field from concentration fronts evolution - is approached. At the reservoir scale, the work will mainly be focused on the integration of 4D-seismic data into inversion programs on a 3D synthetic case. A particular importance will be given to the calculation of gradients, in order to obtain a complementary information about the sensitivity of data. The information provided by 4D-seismic data consists in maps showing the vertical average of oil saturation or the presence of gas. The purpose is to integrate this qualitative information in the inversion process and to evaluate the impact on the reservoir characterization. Comparative studies - with or without 4D-seismic data - will be realized on a synthetic case. (author)

  8. Numerical modelling of two phase flow with hysteresis in heterogeneous porous media

    Energy Technology Data Exchange (ETDEWEB)

    Abreu, E. [Instituto Nacional de Matematica Pura e Aplicada (IMPA), Rio de Janeiro, RJ (Brazil); Furtado, F.; Pereira, F. [University of Wyoming, Laramie, WY (United States). Dept. of Mathematicsatics; Souza, G. [Universidade do Estado do Rio de Janeiro (UERJ), RJ (Brazil)

    2008-07-01

    Numerical simulators are necessary for the understanding of multiphase flow in porous media in order to optimize hydrocarbon recovery. In this work, the immiscible flow of two incompressible phases, a problem very common in waterflooding of petroleum reservoirs, is considered and numerical simulation techniques are presented. The system of equations which describe this type of flow form a coupled, highly nonlinear system of time-dependent partial differential equations (PDEs). The equation for the saturation of the invading fluid is a convection-dominated, degenerate parabolic PDE whose solutions typically exhibit sharp fronts (i.e., internal layers with strong gradients) and is very difficult to approximate numerically. It is well known that accurate modeling of convective and diffusive processes is one of the most daunting tasks in the numerical approximation of PDEs. Particularly difficult is the case where convection dominates diffusion. Specifically, we consider the injection problem for a model of two-phase (water/oil) flow in a core sample of porous rock, taking into account hysteresis effects in the relative permeability of the oil phase. (author)

  9. Continuous-Flow Processes in Heterogeneously Catalyzed Transformations of Biomass Derivatives into Fuels and Chemicals

    Directory of Open Access Journals (Sweden)

    Antonio A. Romero

    2012-07-01

    Full Text Available Continuous flow chemical processes offer several advantages as compared to batch chemistries. These are particularly relevant in the case of heterogeneously catalyzed transformations of biomass-derived platform molecules into valuable chemicals and fuels. This work is aimed to provide an overview of key continuous flow processes developed to date dealing with a series of transformations of platform chemicals including alcohols, furanics, organic acids and polyols using a wide range of heterogeneous catalysts based on supported metals, solid acids and bifunctional (metal + acidic materials.

  10. Migration and Entrapment of DNAPLs in Heterogeneous Systems: Impact of Waste and Porous Medium Composition

    Energy Technology Data Exchange (ETDEWEB)

    Linda M. Abriola; Avery H. Demond

    2005-01-10

    Dense nonaqueous phase liquids (DNAPLs) pose a significant threat to soil and groundwater at Department of Energy (DOE) sites. Evidence suggests that subsurface wettability variations are present at many of these sites as a result of spatical and temporal variations in aqueous phase chemistry, contaminant aging, mineralogy and organic matter. The presence of such heterogeneity may significantly influence DNAPL migration and entrapment in the saturated zone.

  11. Lattice Boltzmann simulation of immiscible fluid displacement in porous media: Homogeneous versus heterogeneous pore network

    International Nuclear Information System (INIS)

    Injection of anthropogenic carbon dioxide (CO2) into geological formations is a promising approach to reduce greenhouse gas emissions into the atmosphere. Predicting the amount of CO2 that can be captured and its long-term storage stability in subsurface requires a fundamental understanding of multiphase displacement phenomena at the pore scale. In this paper, the lattice Boltzmann method is employed to simulate the immiscible displacement of a wetting fluid by a non-wetting one in two microfluidic flow cells, one with a homogeneous pore network and the other with a randomly heterogeneous pore network. We have identified three different displacement patterns, namely, stable displacement, capillary fingering, and viscous fingering, all of which are strongly dependent upon the capillary number (Ca), viscosity ratio (M), and the media heterogeneity. The non-wetting fluid saturation (Snw) is found to increase nearly linearly with logCa for each constant M. Increasing M (viscosity ratio of non-wetting fluid to wetting fluid) or decreasing the media heterogeneity can enhance the stability of the displacement process, resulting in an increase in Snw. In either pore networks, the specific interfacial length is linearly proportional to Snw during drainage with equal proportionality constant for all cases excluding those revealing considerable viscous fingering. Our numerical results confirm the previous experimental finding that the steady state specific interfacial length exhibits a linear dependence on Snw for either favorable (M ≥ 1) or unfavorable (M < 1) displacement, and the slope is slightly higher for the unfavorable displacement

  12. Heterogeneous nucleation - current transients under chemical reaction control

    CERN Document Server

    D'Ajello-Tettamanzy, P C; Kipervaser, Z G S

    2002-01-01

    Heterogeneous nucleation on catalytic surfaces plunged into a fluid is described through a stochastic model. To generate this non-equilibrium process we assume that the turn on of a electrostatic potential triggers a complex dynamics that includes a free Brownian motion, a reaction kinetic and a stimulated migration before the final adhesion of ions on the surface (electrode). At, when the potential is switched on, the spatial symmetry is broken and a two-stage process is developed. First the ion undergoes a change in its electrochemical character (at some region of the space) and then reacts at some specific points to stick together on the surface. The continuous addition of ions develops a material deposit connected to the current transient signals measured in electrochemical deposition processes. Unlike current models found in the literature, this procedure avoids the computation of the area covered by the diffusion zones, allowing a formalism skill to describe equally well the absorption of ions by channe...

  13. Evidence for chemically heterogeneous Arctic mantle beneath the Gakkel Ridge

    Science.gov (United States)

    D'Errico, Megan E.; Warren, Jessica M.; Godard, Marguerite

    2016-02-01

    Ultraslow spreading at mid-ocean ridges limits melting due to on-axis conductive cooling, leading to the prediction that peridotites from these ridges are relatively fertile. To test this, we examined abyssal peridotites from the Gakkel Ridge, the slowest spreading ridge in the global ocean ridge system. Major and trace element concentrations in pyroxene and olivine minerals are reported for 14 dredged abyssal peridotite samples from the Sparsely Magmatic (SMZ) and Eastern Volcanic (EVZ) Zones. We observe large compositional variations among peridotites from the same dredge and among dredges in close proximity to each other. Modeling of lherzolite trace element compositions indicates varying degrees of non-modal fractional mantle melting, whereas most harzburgite samples require open-system melting involving interaction with a percolating melt. All peridotite chemistry suggests significant melting that would generate a thick crust, which is inconsistent with geophysical observations at Gakkel Ridge. The refractory harzburgites and thin overlying oceanic crust are best explained by low present-day melting of a previously melted heterogeneous mantle. Observed peridotite compositional variations and evidence for melt infiltration demonstrates that fertile mantle components are present and co-existing with infertile mantle components. Melt generated in the Gakkel mantle becomes trapped on short length-scales, which produces selective enrichments in very incompatible rare earth elements. Melt migration and extraction may be significantly controlled by the thick lithosphere induced by cooling at such slow spreading rates. We propose the heterogeneous mantle that exists beneath Gakkel Ridge is the consequence of ancient melting, combined with subsequent melt percolation and entrapment. Initial modes of depleted mantle composition from Hellebrand et al. (2002b). Melt compositions are from Brunelli et al. (2014) in Table 1.

  14. Wetting heterogeneity in mixed-wet porous media controls flow dissipation

    CERN Document Server

    Murison, Julie; Baret, Jean-Christophe; Herminghaus, Stephan; Schröter, Matthias; Brinkmann, Martin

    2013-01-01

    Wettability is crucial for multiphase flow in porous media. However, the effect of spatial distribution of wetting domains has previously only been dealt with by averaging contact angles over several pores. By preparing tailored bead packings with the same average surface wettability, but differing in the typical spatial extension of the same-type wetting domains, we show that models based solely on averages do not capture the dynamics of two phase flow in such systems. Using X-ray tomography we measure the typical length scale xi of the wetting domains in our samples. In capillary pressure saturation (CPS) experiments we find that xi controls the width of the hysteresis loop for xi <= d, d being the bead diameter. X-Ray tomography of the samples during both water and oil invasion shows that the front morphology is smoothened at small values of xi. Both observations are consistent with an increase of dissipation for small correlation length.

  15. Heterogeneously Catalyzed Valorization of Monoterpenes to High Value-Added Chemicals

    OpenAIRE

    Golets, Mikhail

    2014-01-01

    A potential industrial process is profitable only if it is successfully implemented by the continuously developing chemical industry. Throughout last decades heterogeneous catalysis has opened doors to the creation of various know-how products which previously were considered unfeasible. Moreover, the use of heterogeneous catalysts allows improving existing processes to shift towards more ecological and cost efficient practices. In particular, polymer or fuel compounds could be eco-friendly p...

  16. Lattice Boltzmann simulation of immiscible fluid displacement in porous media: Homogeneous versus heterogeneous pore network

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Haihu, E-mail: haihu.liu@mail.xjtu.edu.cn [School of Energy and Power Engineering, Xi’an Jiaotong University, 28 West Xianning Road, Xi’an 710049 (China); James Weir Fluids Laboratory, Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ (United Kingdom); Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); Zhang, Yonghao [James Weir Fluids Laboratory, Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ (United Kingdom); Valocchi, Albert J. [Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

    2015-05-15

    Injection of anthropogenic carbon dioxide (CO{sub 2}) into geological formations is a promising approach to reduce greenhouse gas emissions into the atmosphere. Predicting the amount of CO{sub 2} that can be captured and its long-term storage stability in subsurface requires a fundamental understanding of multiphase displacement phenomena at the pore scale. In this paper, the lattice Boltzmann method is employed to simulate the immiscible displacement of a wetting fluid by a non-wetting one in two microfluidic flow cells, one with a homogeneous pore network and the other with a randomly heterogeneous pore network. We have identified three different displacement patterns, namely, stable displacement, capillary fingering, and viscous fingering, all of which are strongly dependent upon the capillary number (Ca), viscosity ratio (M), and the media heterogeneity. The non-wetting fluid saturation (S{sub nw}) is found to increase nearly linearly with logCa for each constant M. Increasing M (viscosity ratio of non-wetting fluid to wetting fluid) or decreasing the media heterogeneity can enhance the stability of the displacement process, resulting in an increase in S{sub nw}. In either pore networks, the specific interfacial length is linearly proportional to S{sub nw} during drainage with equal proportionality constant for all cases excluding those revealing considerable viscous fingering. Our numerical results confirm the previous experimental finding that the steady state specific interfacial length exhibits a linear dependence on S{sub nw} for either favorable (M ≥ 1) or unfavorable (M < 1) displacement, and the slope is slightly higher for the unfavorable displacement.

  17. Chemical synthesis of porous web-structured CdS thin films for photosensor applications

    International Nuclear Information System (INIS)

    The photo-activity of chemically deposited cadmium sulphide (CdS) thin film has been studied. The simple chemical route nucleates the CdS films with size up to the mean free path of the electron. Growth Kinematics of crystalline hexagonal CdS phase in the thin film form was monitored using X-ray diffraction. The time limitation set for the formation of the amorphous/nano-crystalline material is 40 and 60 min. Thereafter enhancement of the crystalline orientation along the desired plane was identified. Web-like porous structured surface morphology of CdS thin film over the entire area is observed. With decrease in synthesis time, increase of band gap energy i.e., a blue spectral shift was seen. The activation energy of CdS thin film at low and high temperature region was examined. It is considered that this activation energy corresponds to the donor levels associated with shallow traps or surface states of CdS thin film. The photo-electrochemical performance of CdS thin films in polysulphide electrolyte showed diode-like characteristics. Exposure of light on the CdS electrode increases the photocurrent. This suggests the possibility of production of free carriers via excited ions and also the light harvesting mechanism due to porous web-structured morphology. These studies hint that the obtained CdS films can work as a photosensor. - Highlights: • Photoactivity of chemically synthesized cadmium sulphide (CdS) thin films was studied. • Web-like porous structured surface morphology of CdS thin film over the entire area was observed. • Blue spectral shift with lowering of the synthesis time suggests films can act as a window layer over the absorber layer. • Porous web-structured CdS thin films can be useful in light harvesting

  18. Development of models for fast fluid pathways through unsaturated heterogeneous porous media

    International Nuclear Information System (INIS)

    The pre-waste-emplacement ground water travel time requirement is a regulatory criterion that specifies ground water travel time to the accessible environment shall be greater than 1,000 years. Satisfying the ground water travel time criterion for the potential repository at Yucca Mountain requires the study of fast travel path formation in the unsaturated zone and development of models that simulate the formation of fast paths. Conceptual models for unsaturated flow that have been used for total-systems performance assessment generally fall into the categories of composite-porosity or fracture models. The actual hydrologic conditions at Yucca Mountain are thought to lie somewhere between the extremes of these two types of models. The current study considers the effects of heterogeneities on composite-porosity models and seeks to develop numerical methods (and models) that can produce locally saturated zones where fracture flow can occur. The credibility of the model and numerical methods is investigated by using test data from the INTRAVAL project (Swedish Nuclear Inspectorate, 1992) to attempt to predict in-situ volumetric water content at specific locations in Yucca Mountain. Work based on the numerical methods presented in this study is eventually intended to allow the calculation of ground water travel times in heterogeneous media. 60 refs

  19. Flow over and within large-scale porous topography: Impact of surface heterogeneity on turbulence structure

    Science.gov (United States)

    Hamed, Ali M.; Ranjan, Prateek; Sadowski, Matthew J.; Nepf, Heidi M.; Chamorro, Leonardo P.

    2015-11-01

    An experimental investigation of the flow within and above model canopies was carried out to determine the effect of canopy height heterogeneity on the structure and spatial distribution of the turbulence. Two 800 mm long models with 20% blockage were placed in a 2.5 m long refractive-index-matching channel. The first model (base case) is constituted of equal height (h) square bar elements arranged in a staggered configuration. The other model bars had two heights (h +1/3h and h-1/3h) alternated every two rows. Particle image velocimetry was used to map the flow field at three locations spanning the length of the canopy under three confinement ratios H/h =2, 3, and 4, where H is the free surface height. The experiments were performed at Reynolds number ReH = 6800 , 10200, and 13600. Refractive index matching renders the canopy invisible and grants full optical access allowing the flow field within the canopy to be measured by PIV. Turbulence statistics complemented with POD, quadrant analysis, and LES decomposition reveal the distinctive effect of the height heterogeneity on the shear layer that forms on top of the canopy, and on the free flow over the canopies.

  20. Effects of heterogeneous porous geology on ground-water flow and transport modeling in multiaquifer systems

    Energy Technology Data Exchange (ETDEWEB)

    Stephenson, D.E.; Duffield, G.M.; Buss, D.R.; Wadsworth, T.D.

    1989-01-01

    A three-dimensional model was used to investigate the influence of simple heterogeneities and discontinuities in an acquitard on ground-water flow and transport in a 17 mi/sup 2/ region of Savannah River Plant (SRP) where geologic and hydrologic control exists. Simple ''holes'' and faults in the confining bed were studied. These features produced variations in the distribution of hydraulic heads that could be difficult to detect without closely spaced monitoring wells in the vicinity of the feature. In terms of solute transport, however, significant changes in flow directions and rates resulted from the presence of the feature. The simulations showed that such heterogeneities and discontinuities can reverse flow directions near the feature and significantly reduce contaminant travel times to lower aquifers. The results of these model simulations indicate the importance of adequate geologic control for the accurate prediction of ground-water flowpaths in multiaquifer systems with implications for ground-water monitoring strategies, remedial system design, and risk assessments. 18 refs., 18 figs.

  1. Development of models for fast fluid pathways through unsaturated heterogeneous porous media

    Energy Technology Data Exchange (ETDEWEB)

    Robey, T.H. [Spectra Research Inst., Albuquerque, NM (United States)

    1994-11-01

    The pre-waste-emplacement ground water travel time requirement is a regulatory criterion that specifies ground water travel time to the accessible environment shall be greater than 1,000 years. Satisfying the ground water travel time criterion for the potential repository at Yucca Mountain requires the study of fast travel path formation in the unsaturated zone and development of models that simulate the formation of fast paths. Conceptual models for unsaturated flow that have been used for total-systems performance assessment generally fall into the categories of composite-porosity or fracture models. The actual hydrologic conditions at Yucca Mountain are thought to lie somewhere between the extremes of these two types of models. The current study considers the effects of heterogeneities on composite-porosity models and seeks to develop numerical methods (and models) that can produce locally saturated zones where fracture flow can occur. The credibility of the model and numerical methods is investigated by using test data from the INTRAVAL project (Swedish Nuclear Inspectorate, 1992) to attempt to predict in-situ volumetric water content at specific locations in Yucca Mountain. Work based on the numerical methods presented in this study is eventually intended to allow the calculation of ground water travel times in heterogeneous media. 60 refs.

  2. Contaminant tailing in highly heterogeneous porous formations: Sensitivity on model selection and material properties

    Science.gov (United States)

    Maghrebi, Mahdi; Jankovic, Igor; Weissmann, Gary S.; Matott, L. Shawn; Allen-King, Richelle M.; Rabideau, Alan J.

    2015-12-01

    Coupled impacts of slow advection, diffusion and sorption were investigated using two heterogeneity models that differ in structure and in the mathematical framework that was used to simulate flow and transport and to quantify contaminant tailing. Both models were built using data from a highly heterogeneous exposure of the Borden Aquifer at a site located 2 km north-west of the Stanford-Waterloo experimental site at Canadian Forces Base Borden, Ontario, Canada. The inclusions-based model used a simplified representation of the different materials found at the site, while the second model was based on transitional probability geostatistics of the formation. These two models were used to investigate sensitivity of contaminant tailing on model selection and on geometric and material properties. While simulations were based on data collected at Borden, models were exercised beyond the geometric and material properties that characterize the site. Various realizations have identified very low conductive silty clay, found at volume fraction of 23.4%, as the material with dominant influence on tailing, and vertical diffusion in and out of low conductive units, affected by sorption, as the dominant transport mechanism causing tailing. The two models yielded almost identical transport results when vertical correlation lengths of silty clay were matched. Several practical implications relevant for characterization of low conductive units were identified and briefly discussed.

  3. To Model Chemical Reactivity in Heterogeneous Emulsions, Think Homogeneous Microemulsions.

    Science.gov (United States)

    Bravo-Díaz, Carlos; Romsted, Laurence Stuart; Liu, Changyao; Losada-Barreiro, Sonia; Pastoriza-Gallego, Maria José; Gao, Xiang; Gu, Qing; Krishnan, Gunaseelan; Sánchez-Paz, Verónica; Zhang, Yongliang; Dar, Aijaz Ahmad

    2015-08-25

    Two important and unsolved problems in the food industry and also fundamental questions in colloid chemistry are how to measure molecular distributions, especially antioxidants (AOs), and how to model chemical reactivity, including AO efficiency in opaque emulsions. The key to understanding reactivity in organized surfactant media is that reaction mechanisms are consistent with a discrete structures-separate continuous regions duality. Aggregate structures in emulsions are determined by highly cooperative but weak organizing forces that allow reactants to diffuse at rates approaching their diffusion-controlled limit. Reactant distributions for slow thermal bimolecular reactions are in dynamic equilibrium, and their distributions are proportional to their relative solubilities in the oil, interfacial, and aqueous regions. Our chemical kinetic method is grounded in thermodynamics and combines a pseudophase model with methods for monitoring the reactions of AOs with a hydrophobic arenediazonium ion probe in opaque emulsions. We introduce (a) the logic and basic assumptions of the pseudophase model used to define the distributions of AOs among the oil, interfacial, and aqueous regions in microemulsions and emulsions and (b) the dye derivatization and linear sweep voltammetry methods for monitoring the rates of reaction in opaque emulsions. Our results show that this approach provides a unique, versatile, and robust method for obtaining quantitative estimates of AO partition coefficients or partition constants and distributions and interfacial rate constants in emulsions. The examples provided illustrate the effects of various emulsion properties on AO distributions such as oil hydrophobicity, emulsifier structure and HLB, temperature, droplet size, surfactant charge, and acidity on reactant distributions. Finally, we show that the chemical kinetic method provides a natural explanation for the cut-off effect, a maximum followed by a sharp reduction in AO efficiency with

  4. Pore Scale Heterogeneity in the Mineral Distribution and Surface Area of Porous Rocks

    Science.gov (United States)

    Lai, Peter; Krevor, Sam

    2015-04-01

    An important control on rate of interfacial processes between minerals and aqueous solutions such as nucleation of solids, and mineral dissolution and growth is reactive surface area. In geochemical modelling, the continuum hypothesis is based on the assumption that the system can be represented by a sufficiently large number of representative elemental volumes. There has been recent interest in studying the impact of this assumption on reaction-transport coupled systems. In this study, the impact of pore-scale heterogeneity on the distribution of reactive surface area is discussed. 3D images obtained using x-ray micro-tomography were used to characterise the distribution of reactive surface area. The results were compared to independent observations. Mineral identification using x- ray diffraction and fluorescence suggested general agreement with CT analysis. Nitrogen BET surface areas were one to two orders of magnitude higher than measurements from x-ray imagery. Co- registered images of Berea sandstone from x-ray and energy dispersive spectroscopy imagery suggested that quartz, K-feldspar and most clays could be identified. However, minor minerals such as albite and illite did not exhibit enough contrast. In Berea sandstone, mineral surface area fraction was poorly correlated to the mineral volumetric fraction. Clay and feldspar minerals exhibited higher surface area fractions than bulk mineralogy suggested. In contrast, in the Edwards carbonate samples, modal mineral composition correlated with mineral-specific surface area. Berea sandstone revealed a characteristic pore size at which a surface area distribution may be used to quantify heterogeneity. Conversely, the carbonate samples suggested a continuous range of pore sizes across length scales. A comparison with pore network model simulations from the literature was made. First order estimates of mineral specific correlations between geometric area measured in the x-ray images were used to convert the CT

  5. Metal transport and chemical heterogeneity in early star forming systems

    Science.gov (United States)

    Ritter, Jeremy S.; Sluder, Alan; Safranek-Shrader, Chalence; Milosavljević, Miloš; Bromm, Volker

    2015-08-01

    To constrain the properties of the first stars with the chemical abundance patterns observed in metal-poor stars, one must identify any non-trivial effects that the hydrodynamics of metal dispersal can imprint on the abundances. We use realistic cosmological hydrodynamic simulations to quantify the distribution of metals resulting from one Population III supernova and from a small number of such supernovae exploding in close succession. Overall, supernova ejecta are highly inhomogeneously dispersed throughout the simulations. When the supernova bubbles collapse, quasi-virialized metal-enriched clouds, fed by fallback from the bubbles and by streaming of metal-free gas from the cosmic web, grow in the centres of the dark matter haloes. Partial turbulent homogenization on scales resolved in the simulation is observed only in the densest clouds where the vortical time-scales are short enough to ensure true homogenization on subgrid scales. However, the abundances in the clouds differ from the gross yields of the supernovae. Continuing the simulations until the cloud have gone into gravitational collapse, we predict that the abundances in second-generation stars will be deficient in the innermost mass shells of the supernova (if only one has exploded) or in the ejecta of the latest supernovae (when multiple have exploded). This indicates that hydrodynamics gives rise to biases complicating the identification of nucleosynthetic sources in the chemical abundance spaces of the surviving stars.

  6. Transport of Organic Oil Components from Immobile and Bypassed Oil in Heterogeneous Porous Media

    Energy Technology Data Exchange (ETDEWEB)

    Huseby, O.; Haugan, A.; Sagen, J.; Muller, J.; Bennett, B.; Larter, S.; Kikkinides, E.S.; Stubos, A.K.; Yousefian, F.; Thovert, J.-F.; Adler, P.M.

    2001-12-01

    An experimental study, as well as theoretical and numerical models, are used to validate a methodology to exploit conventional geochemical data with regard to the concentration profiles of organic components occurring naturally in hydrocarbon reservoir oils. The experiment was designed to study transport of organic compounds from immobile oil during water injection. A homogeneous oil-filled core sample was made heterogeneous by drilling a hole through its central axis and filling it with a highly permeable material. Under the present conditions, diffusion coefficients are the most important parameters controlling the transport, and the effect of partitioning could be accounted for by a simple normalization. The experimental results are well described by a simple 2-D analytical model which assumes instantaneous removal of solutes from the oil-water interface. The experimental results are also well described by two numerical models, of which one is a full featured reservoir scale model, suitable for applications of the methodology to reservoir scale cases. (author)

  7. Comparison of iterative methods and preconditioners for the solution of miscible two-phase flow in heterogeneous porous media

    Science.gov (United States)

    Büsing, Henrik

    2014-05-01

    calculation of mutual solubilities from 12 to 100 °C and up to 600 bar, Geochimica et Cosmochimica Acta, 67(16), 3015-3031. [2] Huber, R. & Helmig, R., 2000. Node-centered finite volume discretizations for the numerical simulation of multiphase flow in heterogeneous porous media, Computational Geosciences, 4, 141-164. [3] Griewank, A. & Walther, A., 2008. Evaluating Derivatives: Principles and Techniques of Algorithmic Differentiation, SIAM, Philadelphia, PA, 2nd edn. [4] Büsing, H., Willkomm, J., Bischof, C. H., & Clauser, C., 2012. Using exact Jacobians in an implicit Newton method for solving multiphase flow in porous media, International Journal for Computational Science and Engineering, (to appear). [5] Pape, H., Clauser, C., & Iffland, J., 2000. Variation of permeability with porosity in sandstone diagenesis interpreted with a fractal pore space model, Pure and Applied Geophysics, 157, 603-619.

  8. Metal Transport and Chemical Heterogeneity in Early Star Forming Systems

    CERN Document Server

    Ritter, Jeremy S; Safranek-Shrader, Chalence; Milosavljevic, Milos; Bromm, Volker

    2014-01-01

    To constrain the properties of the first stars with the chemical abundance patterns observed in metal-poor stars, one must identify any non-trivial effects that the hydrodynamics of metal dispersal can imprint on the abundances. We use realistic cosmological hydrodynamic simulations to quantify the distribution of metals resulting from one Population III supernova and from a small number of such supernovae. Overall, supernova ejecta remain highly inhomogeneous throughout the simulations. When the supernova bubbles collapse, quasi-virialized metal-enriched clouds, fed by fallback from the bubbles and by streaming of metal-free gas from the cosmic web, grow in the centers of the dark matter halos. Partial turbulent homogenization on scales resolved in the simulation is observed in the clouds, and the vortical time scales are short enough to ensure true homogenization on subgrid scales. However, the abundances in the clouds differ from the gross yields of the supernovae. Continuing the simulations until the clou...

  9. Investigation of coupled heat and mass transfer in heterogeneous porous media using numerical simulations

    Science.gov (United States)

    Illangasekare, T. H.; Frippiat, C. C.; Zyvoloski, G. A.

    2007-12-01

    A significant body of knowledge exists on separates processes of thermal and mass transport in granular and fractured subsurface formations. However, the need to simulate these processes in a fully coupled way has become necessary to deal with problems associated with long-term-storage of nuclear waste, and the development of new technologies for subsurface remediation. Another emerging area for research is associated with the development of technologies for in situ extraction of underground resources. Numerical models that couple thermal and mass transport processes will play a crucial role in understanding the fundamental processes associated with these new technologies, as well as in making predictions on how complex subsurface systems are expected to behave. It is our hypothesis that heat transport will have a significant impact on distributions of solute concentration, through temperature-dependent dissolution and precipitation, and temperature-dependent rate-limited diffusive transfer of solutes in fractured or highly heterogeneous media. A number of issues related to the validity of existing numerical tools that capture these processes, and their application to field systems through up-scaling need to be investigated. With this overall goal in mind, in this preliminary study, we explore the effect of the variability of subsurface properties on heat and mass transport using simulations conducted using an existing multiphase model. The finite-element code FEHM (Finite-Element Heat and Mass transport code) used in this study was developed at Los Alamos National Laboratory. This code allows for the coupled simulation of flow, heat and mass transport, accounting for density effects and dissolution and/or precipitation reactions. Our analysis is based on two- and three-dimensional simulations using synthetic data sets. Heterogeneous facies distributions are generated according to Markov Chain transition probability models. A distributed source of constant

  10. Adaptive mesh refinement for a finite volume method for flow and transport of radionuclides in heterogeneous porous media

    International Nuclear Information System (INIS)

    In this paper, we consider adaptive numerical simulation of miscible displacement problems in porous media, which are modeled by single phase flow equations. A vertex-centred finite volume method is employed to discretize the coupled system: the Darcy flow equation and the diffusion-convection concentration equation. The convection term is approximated with a Godunov scheme over the dual finite volume mesh, whereas the diffusion-dispersion term is discretized by piecewise linear conforming finite elements. We introduce two kinds of indicators, both of them of residual type. The first one is related to time discretization and is local with respect to the time discretization: thus, at each time, it provides an appropriate information for the choice of the next time step. The second is related to space discretization and is local with respect to both the time and space variable and the idea is that at each time it is an efficient tool for mesh adaptivity. An error estimation procedure evaluates where additional refinement is needed and grid generation procedures dynamically create or remove fine-grid patches as resolution requirements change. The method was implemented in the software MELODIE, developed by the French Institute for Radiological Protection and Nuclear Safety (IRSN, Institut de Radioprotection et de Surete Nucleaire). The algorithm is then used to simulate the evolution of radionuclide migration from the waste packages through a heterogeneous disposal, demonstrating its capability to capture complex behavior of the resulting flow. (authors)

  11. Adaptive Mesh Refinement for a Finite Volume Method for Flow and Transport of Radionuclides in Heterogeneous Porous Media

    Directory of Open Access Journals (Sweden)

    Amaziane Brahim

    2014-07-01

    Full Text Available In this paper, we consider adaptive numerical simulation of miscible displacement problems in porous media, which are modeled by single phase flow equations. A vertex-centred finite volume method is employed to discretize the coupled system: the Darcy flow equation and the diffusion-convection concentration equation. The convection term is approximated with a Godunov scheme over the dual finite volume mesh, whereas the diffusion-dispersion term is discretized by piecewise linear conforming finite elements. We introduce two kinds of indicators, both of them of residual type. The first one is related to time discretization and is local with respect to the time discretization: thus, at each time, it provides an appropriate information for the choice of the next time step. The second is related to space discretization and is local with respect to both the time and space variable and the idea is that at each time it is an efficient tool for mesh adaptivity. An error estimation procedure evaluates where additional refinement is needed and grid generation procedures dynamically create or remove fine-grid patches as resolution requirements change. The method was implemented in the software MELODIE, developed by the French Institute for Radiological Protection and Nuclear Safety (IRSN, Institut de Radioprotection et de Sûreté Nucléaire. The algorithm is then used to simulate the evolution of radionuclide migration from the waste packages through a heterogeneous disposal, demonstrating its capability to capture complex behavior of the resulting flow.

  12. High-resolution monte carlo simulation of flow and conservative transport in heterogeneous porous media 1. Methodology and flow results

    Science.gov (United States)

    Naff, R.L.; Haley, D.F.; Sudicky, E.A.

    1998-01-01

    In this, the first of two papers concerned with the use of numerical simulation to examine flow and transport parameters in heterogeneous porous media via Monte Carlo methods, Various aspects of the modelling effort are examined. In particular, the need to save on core memory causes one to use only specific realizations that have certain initial characteristics; in effect, these transport simulations are conditioned by these characteristics. Also, the need to independently estimate length Scales for the generated fields is discussed. The statistical uniformity of the flow field is investigated by plotting the variance of the seepage velocity for vector components in the x, y, and z directions. Finally, specific features of the velocity field itself are illuminated in this first paper. In particular, these data give one the opportunity to investigate the effective hydraulic conductivity in a flow field which is approximately statistically uniform; comparisons are made with first- and second-order perturbation analyses. The mean cloud velocity is examined to ascertain whether it is identical to the mean seepage velocity of the model. Finally, the variance in the cloud centroid velocity is examined for the effect of source size and differing strengths of local transverse dispersion.

  13. Numerical research on the anisotropic transport of thermal neutron in heterogeneous porous media with micron X-ray computed tomography

    Science.gov (United States)

    Wang, Yong; Yue, Wenzheng; Zhang, Mo

    2016-06-01

    The anisotropic transport of thermal neutron in heterogeneous porous media is of great research interests in many fields. In this paper, it is the first time that a new model based on micron X-ray computed tomography (CT) has been proposed to simultaneously consider both the separation of matrix and pore and the distribution of mineral components. We apply the Monte Carlo method to simulate thermal neutrons transporting through the model along different directions, and meanwhile detect those unreacted thermal neutrons by an array detector on the other side of the model. Therefore, the anisotropy of pore structure can be imaged by the amount of received thermal neutrons, due to the difference of rock matrix and pore-filling fluids in the macroscopic reaction cross section (MRCS). The new model has been verified by the consistent between the simulated data and the pore distribution from X-ray CT. The results show that the evaluation of porosity can be affected by the anisotropy of media. Based on the research, a new formula is developed to describe the correlation between the resolution of array detectors and the quality of imaging. The formula can be further used to analyze the critical resolution and the suitable number of thermal neutrons emitted in each simulation. Unconventionally, we find that a higher resolution cannot always lead to a better image.

  14. Bayesian uncertainty quantification for flows in heterogeneous porous media using reversible jump Markov chain Monte Carlo methods

    KAUST Repository

    Mondal, A.

    2010-03-01

    In this paper, we study the uncertainty quantification in inverse problems for flows in heterogeneous porous media. Reversible jump Markov chain Monte Carlo algorithms (MCMC) are used for hierarchical modeling of channelized permeability fields. Within each channel, the permeability is assumed to have a lognormal distribution. Uncertainty quantification in history matching is carried out hierarchically by constructing geologic facies boundaries as well as permeability fields within each facies using dynamic data such as production data. The search with Metropolis-Hastings algorithm results in very low acceptance rate, and consequently, the computations are CPU demanding. To speed-up the computations, we use a two-stage MCMC that utilizes upscaled models to screen the proposals. In our numerical results, we assume that the channels intersect the wells and the intersection locations are known. Our results show that the proposed algorithms are capable of capturing the channel boundaries and describe the permeability variations within the channels using dynamic production history at the wells. © 2009 Elsevier Ltd. All rights reserved.

  15. Spectral Quasi-linearization Method for Homogeneous-Heterogeneous Reactions on Nonlinear Convection Flow of Micropolar Fluid Saturated Porous Medium with Convective Boundary Condition

    Science.gov (United States)

    RamReddy, Chetteti; Pradeepa, Teegala

    2016-05-01

    Based on the nonlinear variation of density with temperature (NDT) in the buoyancy term, the mixed convection flow along a vertical plate of a micropolar fluid saturated porous medium is considered. In addition, the effect of homogeneous-heterogeneous reaction and convective boundary condition has been taken into account. Using lie scaling group transformations, the similarity representation is attained for the system of partial differential equations, prior to being solved by a spectral quasilinearization method. The results show that in the presence of aiding and opposing flow situations, both the species concentration and mass transfer rate decreases when the strength of homogeneous and heterogeneous reaction parameters are enhanced.

  16. Probabilistic calculations of groundwater travel time in heterogeneous three-dimensional porous media

    International Nuclear Information System (INIS)

    Groundwater travel time (GWTT) estimation at a potential high-level waste (HLW) repository is subject to various technical uncertainties. These uncertainties stem from model and data uncertainties and cannot be resolved with field tests because of the long time (>1,000 yr) and large space (>5,000 m) scales involved. Therefore, computational methods for demonstrating and determining compliance with the GWTT rule will be used. Stochastic theory based approaches constitute a natural framework for performing GWTT estimations under conditions of uncertain and/or limited data. This study employs the generation of spatially correlated hydraulic conductivity fields by the Nearest Neighbor Model (NNM). Repeated (Monte Carlo) realizations of the statistically equivalent random fields are obtained, and the saturated steady-state groundwater flow equation is solved. These results are then used to estimate GWTT along particular paths by releasing a large number of water particles at various starting points. By doing so, path variability is sampled through the realization ensemble space and also through the independent particle open-quotes flightsclose quotes within a specific flow field realization. The uncertainty in predicted GWTT due to parameter variability is assessed for a data set characteristic of the saturated zone at Yucca Mountain at three levels of parameter heterogeneity. However, since several parameters and the boundary conditions of the problem have been arbitrarily assumed, direct conclusions regarding the proposed Yucca Mountain site cannot be drawn from this study

  17. An Inverse Model of Three-Dimensional Flow and Transport in Heterogeneous Porous Media

    Science.gov (United States)

    Robinson, B. A.; Vrugt, J. A.; Yoon, H.; Zhang, C.; Werth, C. J.; Kitanidis, P. K.; Lichtner, P. C.; Lu, C.

    2007-12-01

    A three-dimensional flow and transport model was developed to simulate the results of a laboratory-scale experiment in which snapshots of concentration were obtained using magnetic resonance imaging (MRI) during the displacement of tracer through a 14 by 8 by 8 cm flow cell. The medium was deliberately constructed to be heterogeneous with a known spatial correlation structure using sand of five different grain-size distributions. The extremely well characterized flow cell and large, high-precision data set of concentrations during displacement make this a unique experiment for examining the validity of flow and transport models, and for exploring new methods for interpreting large data sets using advanced optimization algorithms. A transport model was constructed by solving the steady state flow equations using the Finite Element Heat and Mass (FEHM) code, using FEHM's particle tracking transport model for simulating tracer migration. The particle tracking model was selected so that precise estimates of the transport parameters could be obtained that are not corrupted by numerical dispersion; a large number of particles (typically one million) were required to provide accuracy. The inverse model included nine uncertain parameters, the five permeability values of the individual sand units, and four dispersion/diffusion parameters. The inverse problem was solved with AMALGAM and DREAM, two recently developed self-adaptive multimethod optimization algorithms. The computations were enabled by performing both the transport model and the optimization loop on a high-performance computing cluster. Computational results indicate that parameter estimates and increased understanding of the behavior of the system can be obtained, and significant improvements in the fit to the data over hand calibration can be achieved, using this inverse modeling approach. The study also illustrates that numerical methods that make effective use of high- performance computing resources and

  18. Surface modification of porous poly(tetrafluoraethylene) film by a simple chemical oxidation treatment

    International Nuclear Information System (INIS)

    A simple, inexpensive and environmental chemical treatment process, i.e., treating porous poly(tetrafluoroethylene) (PTFE) films by a mixture of potassium permanganate solution and nitric acid, was proposed to improve the hydrophilicity of PTFE. To evaluate the effectiveness of this strong oxidation treatment, contact angle measurement was performed. The effects of treatment time and temperature on the contact angle of PTFE were studied as well. The results showed that the chemical modification decreased contact angle of as-received PTFE film from 133 ± 3 deg. to 30 ± 4 deg. treated at 100 deg. C for 3 h, effectively converting the hydrophobic PTFE to a hydrophilic PTFE matrix. The changes in chemical structure, surface compositions and crystal structure of PTFE were examined by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD), respectively. It was found that the F/C atomic ratio decreased from untreated 1.65-0.10 treated by the mixture at 100 deg. C for 3 h. Hydrophilic groups such as carbonyl (C=O) and hydroxyl (-OH) were introduced on the surface of PTFE after treatment. Furthermore, hydrophilic compounds K0.27MnO2.0.54H2O was absorbed on the surface of porous PTFE film. Both the introduction of hydrophilic groups and absorption of hydrophilic compounds contribute to the significantly decreased contact angle of PTFE.

  19. Surface modification of porous poly(tetrafluoraethylene) film by a simple chemical oxidation treatment

    Science.gov (United States)

    Wang, Shifang; Li, Juan; Suo, Jinping; Luo, Tianzhi

    2010-01-01

    A simple, inexpensive and environmental chemical treatment process, i.e., treating porous poly(tetrafluoroethylene) (PTFE) films by a mixture of potassium permanganate solution and nitric acid, was proposed to improve the hydrophilicity of PTFE. To evaluate the effectiveness of this strong oxidation treatment, contact angle measurement was performed. The effects of treatment time and temperature on the contact angle of PTFE were studied as well. The results showed that the chemical modification decreased contact angle of as-received PTFE film from 133 ± 3° to 30 ± 4° treated at 100 °C for 3 h, effectively converting the hydrophobic PTFE to a hydrophilic PTFE matrix. The changes in chemical structure, surface compositions and crystal structure of PTFE were examined by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), X-ray diffraction (XRD), respectively. It was found that the F/C atomic ratio decreased from untreated 1.65-0.10 treated by the mixture at 100 °C for 3 h. Hydrophilic groups such as carbonyl (C dbnd O) and hydroxyl ( sbnd OH) were introduced on the surface of PTFE after treatment. Furthermore, hydrophilic compounds K 0.27MnO 2·0.54H 2O was absorbed on the surface of porous PTFE film. Both the introduction of hydrophilic groups and absorption of hydrophilic compounds contribute to the significantly decreased contact angle of PTFE.

  20. On the thermal stability of a chemically reacting gas in a porous sphere

    International Nuclear Information System (INIS)

    The problem is centred around the determination of the stability boundary of a binary mixture of a chemically reacting gas inside a porous sphere in a radially symmetric gravitational field. Under small perturbation theory, the system of nonlinear partial differential equations is reduced to a homogeneous linear eigenvalue problem for the stability parameter. The solution of the eigenvalue problem is reduced to familiar infinite secular determinant by variational formalism. The effect of the reaction rate constant on the stability parameter is discussed quantitatively. The problem is paramount in geophysics. (author). 4 refs, 1 tab

  1. Radiation and chemical reaction effects on MHD flow along a moving vertical porous plate

    Science.gov (United States)

    Ramana Reddy, G. V.; Bhaskar Reddy, N.; Gorla, R. S. R.

    2016-02-01

    This paper presents an analysis of the effects of magnetohydrodynamic force and buoyancy on convective heat and mass transfer flow past a moving vertical porous plate in the presence of thermal radiation and chemical reaction. The governing partial differential equations are reduced to a system of self-similar equations using the similarity transformations. The resultant equations are then solved numerically using the fourth order Runge-Kutta method along with the shooting technique. The results are obtained for the velocity, temperature, concentration, skin-friction, Nusselt number and Sherwood number. The effects of various parameters on flow variables are illustrated graphically, and the physical aspects of the problem are discussed.

  2. Chemical cleaning of porous stainless steel cross-flow filter elements for nuclear waste applications

    International Nuclear Information System (INIS)

    The Waste Treatment and Immobilization Plant (WTP) currently under construction for treatment of High-Level Waste (HLW) at the Hanford Site will rely on cross-flow ultrafiltration to provide solids-liquid separation as a core part of the treatment process. To optimize process throughput, periodic chemical cleaning of the porous stainless steel filter elements has been incorporated into the design of the plant. It is currently specified that chemical cleaning with nitric acid will occur after significant irreversible membrane fouling is observed. Irreversible fouling is defined as fouling that cannot be removed by backpulsing the filter. PNNL has investigated chemical cleaning processes as part of integrated tests with HLW simulants and with actual Hanford tank wastes. To quantify the effectiveness of chemical cleaning, the residual membrane resistance after cleaning was compared against the initial membrane resistance for each test in a series of long-term fouling tests. The impact of the small amount of residual resistance in these tests could not be separated from other parameters and the historical benchmark of >1 GPM/ft2 for clean water flux was determined to be an adequate metric for chemical cleaning. Using the results from these tests, a process optimization strategy is presented suggesting that for the simulant material under test, the value of chemical cleaning may be suspect. The period of enhanced filtration may not be enough to offset the down time required for chemical cleaning, without respect to the other associated costs.

  3. Chemical cleaning of porous stainless steel cross-flow filter elements for nuclear waste applications

    Energy Technology Data Exchange (ETDEWEB)

    Billing, Justin M.; Daniel, Richard C.; Hallen, Richard T.; Schonewill, Philip P.; Shimskey, Rick W.; Peterson, Reid A.

    2011-05-10

    The Waste Treatment and Immobilization Plant (WTP) currently under construction for treatment of High-Level Waste (HLW) at the Hanford Site will rely on cross-flow ultrafiltration to provide solids-liquid separation as a core part of the treatment process. To optimize process throughput, periodic chemical cleaning of the porous stainless steel filter elements has been incorporated into the design of the plant. It is currently specified that chemical cleaning with nitric acid will occur after significant irreversible membrane fouling is observed. Irreversible fouling is defined as fouling that cannot be removed by backpulsing the filter. PNNL has investigated chemical cleaning processes as part of integrated tests with HLW simulants and with actual Hanford tank wastes. To quantify the effectiveness of chemical cleaning, the residual membrane resistance after cleaning was compared against the initial membrane resistance for each test in a series of long-term fouling tests. The impact of the small amount of residual resistance in these tests could not be separated from other parameters and the historical benchmark of >1 GPM/ft2 for clean water flux was determined to be an adequate metric for chemical cleaning. Using the results from these tests, a process optimization strategy is presented suggesting that for the simulant material under test, the value of chemical cleaning may be suspect. The period of enhanced filtration may not be enough to offset the down time required for chemical cleaning, without respect to the other associated costs.

  4. Nature of Non-Fickian Solute Transport in Complex Heterogeneous Porous Media - Carbonates

    Science.gov (United States)

    Bijeljic, B.; Mostaghimi, P.; Blunt, M. J.

    2011-12-01

    Despite the range of significant practical applications of solute transport, including the long-term fate of nuclear waste repositories, secure storage of CO2 and improved oil recovery, even the qualitative behavior of most rocks is uncertain: vast carbonate sedimentary basins contain more than half the world's current oil reserves yet experimental data on transport in carbonates is scant. The relationship between pore structure, velocity field and transport remains unknown, particularly for heterogeneous carbonates. We simulate solute transport through 3D μ-CT images of different rock samples, representing geological media of increasing pore-scale complexity: a sandpack, a Berea sandstone and a Portland limestone. A finite-difference Stokes solver is employed to compute the flow field and transport particles semi-analytically along streamlines to represent advection with a random motion to model diffusion. We predict the propagators measured on similar cores in Nuclear Magnetic Resonance (NMR) experiments. Dispersion coefficient dependence on Peclet number is shown to have different scaling for complex carbonates. The behavior is explained using continuous time random walks with a truncated power-law distribution of travel times: transport is qualitatively different for the complex limestone compared to the sandstone or sandpack, with long tailing, an almost immobile peak concentration and a very slow approach to asymptotic dispersion. We demonstrate the different nature of non-Fickian transport in carbonates by analyzing the transit time probabilities ψ(τ) of traveling between two neighboring voxels for Portland carbonate that show an approximately power-law dependence of travel times ψ(τ) ~ τ -1-β with a slope corresponding to β = 0.7, as shown in Fig.1. The comparison with ψ(τ) of the sandpack and Berea sandstone for Pe = ∝ indicates quantitatively different generic behavior, as the sandpack and sandstone have slope corresponding to β = 1.8 (two

  5. Nano-hydroxyapatite colloid suspension coated on chemically modified porous silicon by cathodic bias: a suitable surface for cell culture

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez, Alejandra [Escuela de Quimica, Universidad de Costa Rica, 2060 (Costa Rica); Centro de Electroquimica y Energia Quimica de la Universidad de Costa Rica (CELEQ), Universidad de Costa Rica, 2060 (Costa Rica); Gonzalez, Jerson [Escuela de Quimica, Universidad de Costa Rica, 2060 (Costa Rica); Garcia-Pineres, Alfonso [Escuela de Quimica, Universidad de Costa Rica, 2060 (Costa Rica); Centro de Investigacion en Biologia Celular y Molecular (CIBCM), Universidad de Costa Rica, 2060 (Costa Rica); Montero, Mavis L. [Escuela de Quimica, Universidad de Costa Rica, 2060 (Costa Rica); Centro de Electroquimica y Energia Quimica de la Universidad de Costa Rica (CELEQ), Universidad de Costa Rica, 2060 (Costa Rica); Centro de Ciencia e Ingenieria en Materiales (CICIMA), Universidad de Costa Rica, 2060 (Costa Rica)

    2011-06-15

    The properties of porous silicon make it an interesting material for biological applications. However, porous silicon is not an appropriate surface for cell growth. Surface modification is an alternative that could afford a bioactive material. In this work, we report a method to yield materials by modification of the porous silicon surface with hydroxyapatite of nanometric dimensions, produced using an electrochemical process and coated on macroporous silicon substrates by cathodic bias. The chemical nature of the calcium phosphate deposited on the substrates after the experimental process and the amount of cell growth on these surfaces were characterized. (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. Effects of grain size and structural heterogeneity on the transport and retention of nano-TiO2 in saturated porous media.

    Science.gov (United States)

    Lv, Xueyan; Gao, Bin; Sun, Yuanyuan; Dong, Shunan; Wu, Jichun; Jiang, Beilei; Shi, Xiaoqing

    2016-09-01

    Accurately predicting the fate and transport of nano-TiO2 in porous media is critical to assess its environmental impact. This study was designed to understand the effects of gain size and structural heterogeneity under different ionic strength (IS) on the fate and transport of nano-TiO2 in saturated porous media. In the columns packed homogenously with sand of different grain sizes (920, 550, 390, and 275μm), the transport of nano-TiO2 decreased when the IS increased from 0.1 to 1 or 10mM. For all the three IS conditions, the retention of the nano-TiO2 particles in the columns increased when the gain size decreased, and the mobility of the nano-TiO2 was the lowest in the sand at size of 275μm with recovery rates of 0.30% to 1.72%. The mass recovery rates of TiO2 in other homogeneous columns were higher and ranged from 0.37% to 59.9%. Structural heterogeneity created two flow domains for the retention and transport of nano-TiO2 particles in the saturated porous media. The fast-flow domain dominated the flow and transport processes of the nano-TiO2 in the heterogeneous columns under the tested conditions. As a result, the transport of nano-TiO2 in the heterogeneous porous media was faster and higher than that in the homogeneous columns under similar experimental conditions. Because of the dominance of the fast-flow domain, the recovery rates of the nano-TiO2 in the heterogeneous columns were similar and ranged from 59.8% to 66.9%. These results reflected the importance of preferential flow to the fate and transport of nano-TiO2 particle in porous media. Simulations from a two-domain model matched the experimental breakthrough curves very well. PMID:26774131

  7. Heat and Moisture Transport in Unsaturated Porous Media -- A Coupled Model in Terms of Chemical Potential

    CERN Document Server

    Sullivan, Eric

    2013-01-01

    Transport phenomena in porous media are commonplace in our daily lives. Examples and applications include heat and moisture transport in soils, baking and drying of food stuffs, curing of cement, and evaporation of fuels in wild fires. Of particular interest to this study are heat and moisture transport in unsaturated soils. Historically, mathematical models for these processes are derived by coupling classical Darcy's, Fourier's, and Fick's laws with volume averaged conservation of mass and energy and empirically based source and sink terms. Recent experimental and mathematical research has proposed modifications and suggested limitations in these classical equations. The primary goal of this thesis is to derive a thermodynamically consistent system of equations for heat and moisture transport in terms of the chemical potential that addresses some of these limitations. The physical processes of interest are primarily diffusive in nature and, for that reason, we focus on using the macroscale chemical potentia...

  8. Internal Domains of Natural Porous Media Revealed: Critical Locations for Transport, Storage, and Chemical Reaction

    Energy Technology Data Exchange (ETDEWEB)

    Zachara, John M.; Brantley, Susan L.; Chorover, Jon D.; Ewing, Robert P.; Kerisit, Sebastien N.; Liu, Chongxuan; Perfect, E.; Rother, Gernot; Stack, Andrew G.

    2016-03-16

    Internal pore domains exist within rocks, lithic fragments, subsurface sediments and soil aggregates. These domains, which we term internal domains in porous media (IDPM), contain a significant fraction of their porosity as nanopores, dominate the reactive surface area of diverse porous media types, and are important locations for chemical reactivity and hydrocarbon storage. Traditionally difficult to interrogate, advances in instrumentation and imaging methods are providing new insights on the physical structures and chemical attributes of IDPM. In this review we: discuss analytical methods to characterize IDPM, evaluate what has been learned about their size distributions, connectivity, and extended structures; determine whether they exhibit unique chemical reactivity; and assess potential for their inclusion in reactive transport models. Three key findings are noteworthy. 1) A combination of methods now allows complete characterization of the porosity spectrum of natural materials and its connectivity; while imaging microscopies are providing three dimensional representations of the interconnected pore network. 2) Chemical reactivity in pores <10 nm is expected to be different from micro and macropores, yet research performed to date is inconclusive on the nature, direction, and magnitude of effect. 3) Existing continuum reactive transport models treat IDPM as a sub-grid feature with average, empirical, scale-dependent parameters; and are not formulated to include detailed information on pore networks. Overall we find that IDPM are key features controlling hydrocarbon release from shales in hydrofracking systems, organic matter stabilization and recalcitrance in soil, weathering and soil formation, and long term inorganic and organic contaminant behavior in the vadose zone and groundwater. We conclude with an assessment of impactful research opportunities to advance understanding of IDPM, and to incorporate their important effects in reactive transport models

  9. Overcoming Heterogeneity Effects Through Polymer-Enhanced Groundwater Remediation Techniques: Coupling Polymer Floods with Chemical Oxidants and Bio-agents

    Science.gov (United States)

    Smith, M. M.; Silva, J. A.; Munakata-Marr, J.; McCray, J. E.

    2008-12-01

    Even small heterogeneity contrasts in contaminated systems (resulting from differences in permeability or contaminant saturation) can affect the distribution of injected remediation agents by channeling fluids through high-permeability flowpaths, thus bypassing some regions and leaving contaminants uncontacted. The addition of a viscous polymer solution to the remediation agent may enhance agent delivery as a result of increased cross-flow (or "sweep efficiency") into different layers of the system, if the polymer solution remains stable in the presence of the remediation agent. Our research combines various non-toxic, food- grade polymer solutions with the remediation techniques of chemical oxidation and bio-remediation, to increase the effectiveness of treatment at sites contaminated with non-aqueous phase liquids (NAPLs). The coupling of polymer floods with oxidants may help to combat contaminant "rebound" sometimes associated with incomplete contaminant destruction in low-permeability zones. Initial compatibility testing has shown that certain robust polymer/oxidant mixtures possess stable viscosities and pose low additional oxidant demands over multi-day timescales. Transport of these solutions through natural porous media was studied in column experiments, and small two-dimensional experiments with heterogeneous layering were conducted to assess effectiveness of contaminant destruction. Limitations of these compatible polymer/oxidant combinations as well as possible experimental strategies to optimize delivery are also discussed. In addition, results of polymer/microbial screening tests reveal that polymer solutions do not inhibit the dechlorinating capabilities of a microbial consortium. Preliminary findings have also raised the possibility that certain polymers may successfully serve as electron donors in the subsurface. The implications of these results for either bioaugmentation or delivery of biostimulants are presented.

  10. Faradiac Impedance of a Heterogeneous Chemical Reaction and an Adsorption Process

    OpenAIRE

    Qudah MMA

    2015-01-01

    The electrochemical behaviour of stainless steel 302 has been investigated in 0.10 M K2SO4 solution using the impedance technique at several anodic potentials. Stainless steel 302 is passive up to 1300 mV, due to the main formation of Cr2O3. Above this potential stainless steel became active. Faradiac impedances of a heterogeneous chemical reaction and an adsorption process were discussed.

  11. Numerical modeling of 1D heterogeneous combustion in porous media under free convection taking into account dependence of permeability on porosity

    Science.gov (United States)

    Lutsenko, N. A.

    2016-06-01

    Using numerical experiment the one-dimensional unsteady process of heterogeneous combustion in porous object under free convection is considered when the dependence of permeability on porosity is taken into account. The combustion is due to exothermic reaction between the fuel in the solid porous medium and oxidizer contained in the gas flowing through the porous object. In the present work the process is considered under natural convection, i.e. when the flow rate and velocity of the gas at the inlet to the porous objects are unknown, but the gas pressure at object boundaries is known. The influence of changing of permeability due to the changing of porosity on the solution is investigated using original numerical method, which is based on a combination of explicit and implicit finite-difference schemes. It was shown that taking into account the dependence of permeability on porosity, which is described by some known equations, can significantly change the solution in one-dimensional case. The changing of permeability due to the changing of porosity leads to the speed increasing of both cocurrent and the countercurrent combustion waves, and to the temperature increasing in the combustion zone of countercurrent combustion wave.

  12. Preparation and structure of porous dielectrics by plasma enhanced chemical vapor deposition

    International Nuclear Information System (INIS)

    The preparation of ultralow dielectric constant porous silicon, carbon, oxygen, hydrogen alloy dielectrics, called 'pSiCOH', using a production 200 mm plasma enhanced chemical vapor deposition tool and a thermal treatment is reported here. The effect of deposition temperature on the pSiCOH film is examined using Fourier transform infrared (FTIR) spectroscopy, dielectric constant (k), and film shrinkage measurements. For all deposition temperatures, carbon in the final porous film is shown to be predominantly Si-CH3 species, and lower k is shown to correlate with increased concentration of Si-CH3. NMR and FTIR spectroscopies clearly detect the loss of a removable, unstable, hydrocarbon (CHx) phase during the thermal treatment. Also detected are increased cross-linking of the Si-O skeleton, and concentration changes for three distinct structures of carbon. In the as deposited films, deposition temperature also affects the hydrocarbon (CHx) content and the presence of C=O and C=C functional groups

  13. Electrochromic properties of porous NiO thin films prepared by a chemical bath deposition

    Energy Technology Data Exchange (ETDEWEB)

    Xia, X.H.; Tu, J.P.; Zhang, J.; Wang, X.L. [Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027 (China); Zhang, W.K.; Huang, H. [College of Chemical Engineering and Materials Science, Zhejiang University of Technology, Hangzhou 310032 (China)

    2008-06-15

    Highly porous nickel oxide thin films were prepared on ITO glass by a simple chemical bath deposition (CBD) method in combination with a following heat-treatment process. XRD analysis revealed that the as-deposited precursor film contained {beta}-Ni(OH){sub 2} and {gamma}-NiOOH, and they changed to cubic polycrystalline NiO after annealing. The FTIR results showed presence of free hydroxyl ion and water in the NiO thin films. The electrochromic properties of NiO thin films were investigated in an aqueous alkaline electrolyte (1 M KOH) by means of transmittance, cyclic voltammetry (CV) and chronoamperometry (CA) measurements. The NiO thin film annealed at 300 C exhibited a noticeable electrochromism and good memory effect. The coloration efficiency was calculated to be 42 cm{sup 2} C{sup -1} at 550 nm, with a variation of transmittance up to 82%. The porous NiO thin films also showed good reaction kinetics with fast switching speed, and the coloration and bleaching time were 8 and 10 s, respectively. (author)

  14. Biological functionalization and patterning of porous silicon prepared by Pt-assisted chemical etching

    International Nuclear Information System (INIS)

    Porous silicon fabricated via Pt-assisted chemical etching of p-type Si (1 0 0) in 1:1:1 EtOH/HF/H2O2 solution possesses a longer durability in air and in aqueous media than anodized one, which is advantageous for biomedical applications. Its surface SiHx (x = 1 and 2) species can react with 10-undecylenic acid completely under microwave irradiation, and subsequent derivatizations of the end carboxylic acid result in affinity capture of proteins. We applied two approaches to produce protein microarrays: photolithography and spotting. The former provides a homogeneous microarray with a very low fluorescence background, while the latter presents an inhomogeneous microarray with a high noise background.

  15. Chemically grown, porous, nickel oxide thin-film for electrochemical supercapacitors

    Energy Technology Data Exchange (ETDEWEB)

    Inamdar, A.I.; Kim, YoungSam; Im, Hyunsik [Department of Semiconductor Science, Dongguk University, Seoul 100-715 (Korea, Republic of); Pawar, S.M.; Kim, J.H. [Department of Materials Science and Engineering, Chonnam National University, Gwangju 500-757 (Korea, Republic of); Kim, Hyungsang [Department of Physics, Dongguk University, Seoul 100-715 (Korea, Republic of)

    2011-02-15

    A porous nickel oxide film is successfully synthesized by means of a chemical bath deposition technique from an aqueous nickel nitrate solution. The formation of a rock salt NiO structure is confirmed with XRD measurements. The electrochemical supercapacitor properties of the nickel oxide film are examined using cyclic voltammetery (CV), galvanostatic and impedance measurements in two different electrolytes, namely, NaOH and KOH. A specific capacitance of {proportional_to}129.5 F g{sup -1} in the NaOH electrolyte and {proportional_to}69.8 F g{sup -1} in the KOH electrolyte is obtained from a cyclic voltammetery study. The electrochemical stability of the NiO electrode is observed for 1500 charge-discharge cycles. The capacitative behaviour of the NiO electrode is confirmed from electrochemical impedance measurements. (author)

  16. Preparation of porous bio-char and activated carbon from rice husk by leaching ash and chemical activation.

    Science.gov (United States)

    Ahiduzzaman, Md; Sadrul Islam, A K M

    2016-01-01

    Preparation porous bio-char and activated carbon from rice husk char study has been conducted in this study. Rice husk char contains high amount silica that retards the porousness of bio-char. Porousness of rice husk char could be enhanced by removing the silica from char and applying heat at high temperature. Furthermore, the char is activated by using chemical activation under high temperature. In this study no inert media is used. The study is conducted at low oxygen environment by applying biomass for consuming oxygen inside reactor and double crucible method (one crucible inside another) is applied to prevent intrusion of oxygen into the char. The study results shows that porous carbon is prepared successfully without using any inert media. The adsorption capacity of material increased due to removal of silica and due to the activation with zinc chloride compared to using raw rice husk char. The surface area of porous carbon and activated carbon are found to be 28, 331 and 645 m(2) g(-1) for raw rice husk char, silica removed rice husk char and zinc chloride activated rice husk char, respectively. It is concluded from this study that porous bio-char and activated carbon could be prepared in normal environmental conditions instead of inert media. This study shows a method and possibility of activated carbon from agro-waste, and it could be scaled up for commercial production. PMID:27536531

  17. Characteristics of lateral heterogeneities with thermal and chemical origins in the pyrolitic lower mantle

    Institute of Scientific and Technical Information of China (English)

    Baosheng Li

    2009-01-01

    The relative changes between shear and compressional velocities (R_(SP)=(e)ln V_S/(e)ln V_P), bulk sound and shear velocities (R_(CS)=(e)ln V_C/(e)ln V_S), and density versus shear wave velocity (R_(PS)=(e)ln ρ/(e)ln V_S) in response to thermal and chemical variations were investigated for the pyrolitic lower mantle. For heterogeneities with thermal origins, R_(SP) increases from 1.7 to 2.0 together with R_(ρS) decreasing from 0.4 to 0.2 and R_(CS)=~0.27 from the top to the bottom of the lower mantle. In comparison, chemical variations (bulk iron or silica contents) are characterized by R_(SP) 0.5 at lower mantle depths. Negative values of R_(ρS) and R_(CS) are indicative of chemical anomalies in the lower mantle, but a combination of thermal and chemical heterogeneities may be required to produce velocity and density anomalies at the magnitudes observed in seismic data. Further refinement of these characteristics requires data on the higher order pressure and temperature derivatives of the elastic moduli of the constituent phases.

  18. Local chemical potentials and pressures in heterogeneous systems: Adsorptive, absorptive, interfaces

    Science.gov (United States)

    Tovbin, Yu. K.

    2016-07-01

    Equations self-consistently describing chemical and mechanical equilibria in heterogeneous systems are derived. The equations are based on the lattice gas model using discrete distributions of molecules in space (on a scale comparable to molecular size) and continuum distributions of molecules (at short distances inside the cells) during their translational and vibrational motions. It is shown that the theory provides a unified description of the equilibrium distributions of molecules in three aggregate states and at their interfaces. Potential functions of intermolecular interactions (such as Mie pair potentials) in several coordination spheres that determine the compressibility of the lattice structure are considered. For simplicity, it is assumed that differences between the sizes of mixture components are small. Expressions for the local components of the pressure tensor inside multicomponent solid phases and heterogeneous systems (adsorptive, absorptive, and interfaces) are obtained. It is established that they can be used to calculate the lattice parameters of deforming phases and the thermodynamic characteristics of interfaces, including surface tension. The tensor nature of the chemical potential in heterogeneous systems is discussed.

  19. Nanofiltration and sensing of picomolar chemical residues in aqueous solution using an optical porous resonator in a microelectrofluidic channel

    Science.gov (United States)

    Huang, Lei; Guo, Zhixiong

    2012-02-01

    For the first time the use of a porous microresonator placed in a microelectrofluidic system for integrated functions of nanofiltration and sensing of small biomolecules and chemical analytes in extremely dilute solution was proposed and investigated. As an example, aminoglycosides in drug residues in food and livestock products were considered as the trace chemical analyte. The filtration process of the charged analyte in aqueous solution driven by an applied electrical field and the accompanying optical whispering-gallery modes in the resonator are modeled. The dynamic process of adsorption and desorption of the analyte onto the porous matrix is studied. Deposition of the analyte inside the porous structure will alter the material refractive index of the resonator, and thus induce an optical resonance frequency shift. By measuring the optical frequency shift, the analyte concentration as well as the absorption/desorption process can be analyzed. Through an intensive numerical study, a correlation between the frequency shift and the analyte concentration and the applied electrical voltage gradient was obtained. This reveals a linear relationship between the resonance frequency shift and the analyte concentration. The applied electrical voltage substantially enhances the filtration capability and the magnitude of the optical frequency shift, pushing the porous resonator-based sensor to function at the extremely dilute picomolar concentration level for small bio/chemical molecules down to the sub-nanometer scale. Moreover, use of the second-order whispering-gallery mode is found to provide better sensitivity compared with the first-order mode.

  20. Nanofiltration and sensing of picomolar chemical residues in aqueous solution using an optical porous resonator in a microelectrofluidic channel

    International Nuclear Information System (INIS)

    For the first time the use of a porous microresonator placed in a microelectrofluidic system for integrated functions of nanofiltration and sensing of small biomolecules and chemical analytes in extremely dilute solution was proposed and investigated. As an example, aminoglycosides in drug residues in food and livestock products were considered as the trace chemical analyte. The filtration process of the charged analyte in aqueous solution driven by an applied electrical field and the accompanying optical whispering-gallery modes in the resonator are modeled. The dynamic process of adsorption and desorption of the analyte onto the porous matrix is studied. Deposition of the analyte inside the porous structure will alter the material refractive index of the resonator, and thus induce an optical resonance frequency shift. By measuring the optical frequency shift, the analyte concentration as well as the absorption/desorption process can be analyzed. Through an intensive numerical study, a correlation between the frequency shift and the analyte concentration and the applied electrical voltage gradient was obtained. This reveals a linear relationship between the resonance frequency shift and the analyte concentration. The applied electrical voltage substantially enhances the filtration capability and the magnitude of the optical frequency shift, pushing the porous resonator-based sensor to function at the extremely dilute picomolar concentration level for small bio/chemical molecules down to the sub-nanometer scale. Moreover, use of the second-order whispering-gallery mode is found to provide better sensitivity compared with the first-order mode. (paper)

  1. Pulsed chemical vapor deposition of Cu2S into a porous TiO2 matrix

    International Nuclear Information System (INIS)

    Chalcocite (Cu2S) has been deposited via pulsed chemical vapor deposition (PCVD) into a porous TiO2 matrix using hydrogen sulfide and a metal-organic precursor. The precursor used is similar to the more common Cu(hfac)(tmvs) precursor, but it is fluorine free and exhibits increased thermal stability. The simultaneous exposure of the substrate to the copper precursor and hydrogen sulfide resulted in nonuniform Cu2S films with a temperature independent deposition rate implying gas phase reaction kinetics. The exposure of mesoporous TiO2 and planar ZnO to alternating cycles of the copper precursor and hydrogen sulfide resulted in a PCVD film that penetrated fully into the porous TiO2 layer with a constant deposition rate of 0.08 nm/cycle over a temperature range of 150-400 deg. C The chalcocite (Cu2S) stoichiometry was confirmed with extended x-ray absorption fine structure measurements (EXAFS) and x-ray photoelectron spectroscopy. Calculations of the EXAFS spectrum for different CuxS phases show that EXAFS is sensitive to the different phase stoichiometries. Optical absorption measurements of CVD thin films using photothermal deflection spectroscopy show the presence of a metallic copper-poor phase for gas phase nucleated films less than 100 nm thick and a copper-rich semiconducting phase for thicknesses greater than 100 nm with a direct band gap of 1.8 eV and an indirect bandgap of 1.2 eV.

  2. Physical and chemical immobilization of choline oxidase onto different porous solid supports: Adsorption studies.

    Science.gov (United States)

    Passos, Marieta L C; Ribeiro, David S M; Santos, João L M; Saraiva, M Lúcia M F S

    2016-08-01

    This work carries out for the first time the comparison between the physical and chemical immobilization of choline oxidase onto aminated silica-based porous supports. The influence on the immobilization efficiency of concentration, pH, temperature and contact time between the support and choline oxidase, was evaluated. The immobilization efficiency was estimated taking into consideration the choline oxidase activity, which was assessed by using cadmium telluride (CdTe) quantum dots (QDs), obtained by hydrothermal synthesis, as photoluminescent probes. Hydrogen peroxide produced by enzyme activity was capable of quenching CdTe QDs photoluminescence. The magnitude of the PL quenching process was directly related with the enzyme activity. By comparing the chemical process with the physical adsorption, it was observed that the latter provided the highest choline oxidase immobilization. The equilibrium data were analyzed using Langmuir and Freundlich isotherms and kinetic data were fitted to the pseudo-first-order and pseudo-second-order models. Thermodynamic parameters, such as Gibbs free energy and entropy were also calculated. These results will certainly contribute to the development of new sensing schemes for choline, taking into account the growing demand for its quantification in biological samples. PMID:27241295

  3. Simulating Thermal-Hydrologic-Mechanical-Chemical Evolution Surrounding Fluid Injection in a Fractured Porous Geothermal Reservoir

    Science.gov (United States)

    Taron, J.; Min, K.; Elsworth, D.

    2006-12-01

    Computational analysis is conducted on the coupled thermal-hydrologic-mechanical-chemical (THMC) behavior of a stimulated EGS geothermal reservoir. Numerical analyses utilize a newly developed simulator capable of examining THMC processes in fractured porous geologic media. The simulator links the thermal-hydrologic- chemical (THC) computational code TOUGHREACT with the mechanical (M) capability of FLAC3D, where the response of pore fluid pressure to mechanical disturbance is treated as an undrained system and mineral precipitation/dissolution generates porosity and permeability change within each dual-permeability continuum. Non-linear permeability response to thermal-hydrologic-mechanical (THM) mechanisms is accommodated via embryonic mechanical and transport constitutive laws, and is considered to act in union with permeability changes associated with the removal or addition of minerals within the system. This construct is applied to the geometry of an injector-withdrawal doublet within the Coso Geothermal field, where in situ stress conditions, thermal state, and mineralogical composition at 3000m depth are extracted from recorded field data. Initial results for feasible parametric settings show that permeability reduction in the vicinity of a cool (80°C) injection well may be significant, within an order of magnitude, and accompanied by large (MPa) changes in the stress field throughout the reservoir for imposed boundary conditions of constant stress.

  4. Optical Characterization of Chemically Etched Nano porous Silicon Embedded in Sol-Gel Matrix

    International Nuclear Information System (INIS)

    Nano porous (NPs) silicon fabricated by chemical etching process in HF acid was first separated in tetrahydrofuran (THF) solvent and then incorporated into SiO2 matrix. The matrix was prepared by sol gel process in which dimethylformamide (DMF) was used as drying chemical control additive (DCCA) to form crack-free dried sample. We examined the optical properties of NPs in three medium which are solvent, sol, and dried sol gel. Our observations reveal that absorption spectra of NPs silicon in THF are modified with respect to the spectra in sol gel. Significant stability in PL of NPs silicon in the sol gel is observed. Influence of matrix environment on peaks of NPs is also discussed. Surface morphology is characterized by field emission scanning electron microscopy (FESEM) which shows that the NPs silicon in THF is similar to the sol gel but becomes aggregation particle to particle. Presence of Si nanoparticles in THF and sol is confirmed by Transmission electron microscopy (TEM). The NPs silicons have mono dispersive and high crystalline nature with spherical shape of around 5 nm in sizes.

  5. Next-Generation Catalysis for Renewables: Combining Enzymatic with Inorganic Heterogeneous Catalysis for Bulk Chemical Production

    DEFF Research Database (Denmark)

    Vennestrøm, Peter Nicolai Ravnborg; Christensen, C.H.; Pedersen, S.;

    2010-01-01

    chemical platform under different conditions than those conventionally employed. Indeed, new process and catalyst concepts need to be established. Both enzymatic catalysis (biocatalysis) and heterogeneous inorganic catalysis are likely to play a major role and, potentially, be combined. One type...... of combination involves one-pot cascade catalysis with active sites from bio- and inorganic catalysts. In this article the emphasis is placed specifically on oxidase systems involving the coproduction of hydrogen peroxide, which can be used to create new in situ collaborative oxidation reactions for bulk...

  6. Line-imaging velocimetry for observing spatially heterogeneous mechanical and chemical responses in plastic bonded explosives during impact.

    Science.gov (United States)

    Bolme, C A; Ramos, K J

    2013-08-01

    A line-imaging velocity interferometer was implemented on a single-stage light gas gun to probe the spatial heterogeneity of mechanical response, chemical reaction, and initiation of detonation in explosives. The instrument is described in detail, and then data are presented on several shock-compressed materials to demonstrate the instrument performance on both homogeneous and heterogeneous samples. The noise floor of this diagnostic was determined to be 0.24 rad with a shot on elastically compressed sapphire. The diagnostic was then applied to two heterogeneous plastic bonded explosives: 3,3(')-diaminoazoxyfurazan (DAAF) and PBX 9501, where significant spatial velocity heterogeneity was observed during the build up to detonation. In PBX 9501, the velocity heterogeneity was consistent with the explosive grain size, however in DAAF, we observed heterogeneity on a much larger length scale than the grain size that was similar to the imaging resolution of the instrument. PMID:24007075

  7. An improved design of TRISO particle with porous SiC inner layer by fluidized bed-chemical vapor deposition

    Science.gov (United States)

    Liu, Rongzheng; Liu, Malin; Chang, Jiaxing; Shao, Youlin; Liu, Bing

    2015-12-01

    Tristructural-isotropic (TRISO) particle has been successful in high temperature gas cooled reactor (HTGR), but an improved design is required for future development. In this paper, the coating layers are reconsidered, and an improved design of TRISO particle with porous SiC inner layer is proposed. Three methods of preparing the porous SiC layer, called high methyltrichlorosilane (MTS) concentration method, high Ar concentration method and hexamethyldisilane (HMDS) method, are experimentally studied. It is indicated that porous SiC layer can be successfully prepared and the density of SiC layer can be adjusted by tuning the preparation parameters. Microstructure and characterization of the improved TRISO coated particle are given based on scanning electron microscope (SEM), X-ray diffraction (XRD), Raman scattering and energy dispersive X-ray (EDX) analysis. It can be found that the improved TRISO coated particle with porous SiC layer can be mass produced successfully. The formation mechanisms of porous SiC layer are also discussed based on the fluidized bed-chemical vapor deposition principle.

  8. Strategies for the chemical analysis of highly porous bone scaffolds using secondary ion mass spectrometry

    International Nuclear Information System (INIS)

    Understanding the distribution of critical elements (e.g. silicon and calcium) within silica-based bone scaffolds synthesized by different methods is central to the optimization of these materials. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been used to determine this information due to its very high surface sensitivity and its ability to map all the elements and compounds in the periodic table with high spatial resolution. The SIMS image data can also be combined with depth profiles to construct three-dimensional chemical maps. However, the scaffolds have interconnected pore networks, which are very challenging structures for the SIMS technique. To overcome this problem two experimental methodologies have been developed. The first method involved the use of the focused ion beam technique to obtain clear images of the regions of interest and subsequently mark them by introducing fiducial marks; the samples were then analysed using the ToF-SIMS technique to yield the chemical analyses of the regions of interest. The second method involved impregnating the pores using a suitable reagent so that a flat surface could be achieved, and this was followed by secondary ion mapping and 3D chemical imaging with ToF-SIMS. The samples used in this work were sol–gel 70S30C foam and electrospun fibres and calcium-containing silica/gelatin hybrid scaffolds. The results demonstrate the feasibility of both these experimental methodologies and indicate that these methods can provide an opportunity to compare various artificial bone scaffolds, which will be of help in improving scaffold synthesis and processing routes. The techniques are also transferable to many other types of porous material. (paper)

  9. Spatial heterogeneity of soil chemical properties between Haloxylon persicum and Haloxylon mmodendron populations

    Institute of Scientific and Technical Information of China (English)

    CongJuan LI; Yan LI; Jian MA; LianLian FAN; QinXue WANG

    2010-01-01

    Spatial heterogeneity is a ubiquitous feature in natural ecosystems,especially in arid regions.Different species and their discontinuous distribution,accompanied by varied topographic characteristics,result in soil resources distributed differently in different locations,and present significant spatial heterogeneity in desert ecosystems.In this study,conventional and geostatistical methods were used to identify the heterogeneity of soil chemical properties in two desert populations,Haloxylon persicum Bunge ex Boss.,which dominates on the slopes and tops of sand dunes and Haloxylon ammodendron (C.A.Mey.) Bunge,which inhabits interdunes in the Gurbantunggut Desert of Xinjiang,China.The results showed that soil pH,electrical conductivity (EC),soil organic carbon (SOC),available nitrogen (AN) and available phosphorus (AP) were significantly higher in H.ammodendron populations than that in H.persicum.The coefficient of variation (CV) indicated that (1) most parameters presented a moderate degree of variability (10%<CV<100%) except pH in both plots,(2) the variability of soil pH,EC and AP in H.ammodendron populations was higher than that in H.persicum populations,and (3) SOC and AN in H.ammodendron populations were lower than that in H.persicurn populations.Geostatistical analysis revealed a strong spatial dependence (Co/(Co+C)<25%) within the distance of ranges for all tested parameters in both plots.The Kriging-interpolated figures showed that the soil spatial distribution was correlated with the vegetation distribution,individual size of plants,and the topographic features,especially with the plants nearest to sampling points and the topographic features.In each plot,soil EC,SOC,AN and AP presented similar distributions,and fertile islands and salt islands occurred in both plots but did not affect every individual plant,since the sampling distance was larger than the size of such fertile islands.The results of topographic effects on soil heterogeneity suggested

  10. Spatial heterogeneity of soil chemical properties between Haloxylon persicum and Haloxylon ammodendron populations

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Spatial heterogeneity is a ubiquitous feature in natural ecosystems, especially in arid regions. Different species and their discontinuous distribution, accompanied by varied topographic characteristics, result in soil resources distributed differently in different locations, and present significant spatial heterogeneity in desert ecosystems. In this study, conventional and geostatistical methods were used to identify the heterogeneity of soil chemical properties in two desert populations, Haloxylon persicum Bunge ex Boss., which dominates on the slopes and tops of sand dunes and Haloxylon ammodendron (C. A. Mey.) Bunge, which inhabits interdunes in the Gurbantunggut Desert of Xinjiang, China. The results showed that soil pH, electrical conductivity (EC), soil organic carbon (SOC), available nitrogen (AN) and available phosphorus (AP) were significantly higher in H. ammodendron populations than that in H. persicum. The coefficient of variation (CV) indicated that (1) most parameters presented a moderate degree of variability (10% < CV < 100%) except pH in both plots, (2) the variability of soil pH, EC and AP in H. ammodendron populations was higher than that in H. persicum populations, and (3) SOC and AN in H. ammodendron populations were lower than that in H. persicum populations. Geostatistical analysis revealed a strong spatial dependence (C0/(C0+C) < 25%) within the distance of ranges for all tested parameters in both plots. The Kriging-interpolated figures showed that the soil spatial distribution was correlated with the vegetation distribution, individual size of plants, and the topographic features, especially with the plants nearest to sampling points and the topographic features. In each plot, soil EC, SOC, AN and AP presented similar distributions, and fertile islands and salt islands occurred in both plots but did not affect every individual plant, since the sampling distance was larger than the size of such fertile islands. The results of topographic

  11. On the segregation of chemical species in a clear boundary layer over heterogeneous land surfaces

    Directory of Open Access Journals (Sweden)

    H. G. Ouwersloot

    2011-07-01

    Full Text Available We have systematically studied the inability of boundary layer turbulence to efficiently mix reactive species. This creates regions where the species are accumulated in a correlated or anti-correlated way, thereby modifying the mean reactivity. Here, we quantify this modification by the intensity of segregation, IS, and analyse the driving mechanisms: heterogeneity of the surface moisture and heat fluxes, various background wind patterns and non-uniform isoprene emissions. For typical conditions in the Amazon rain forest, applying homogeneous surface forcings, the isoprene-OH reaction rate is altered by less than 10 %. This is substantially smaller than the previously assumed IS of 50 % in recent large-scale model analyses of tropical rain forest chemistry. Spatial heterogeneous surface emissions enhance the segregation of species, leading to alterations of the chemical reaction rates of up to 20 %. For these cases, spatial segregation is induced by heterogeneities of the surface properties: a cool and wet forested patch characterized by high isoprene emissions is alternated with a warm and dry patch that represents pasture with relatively low isoprene emissions. The intensities of segregation are enhanced when the background wind direction is parallel to the borders between the patches and reduced in case of a perpendicular wind direction. The effects of segregation on trace gas concentrations vary per species. For the highly reactive OH, the differences in concentration averaged over the boundary layer are less than 2 % compared to homogeneous surface conditions, while the isoprene concentration is increased by as much as 12 % due to the reduced chemical reaction rates. These processes take place at the sub-grid scale of chemistry transport models and therefore need to be parameterized.

  12. Problems of application of porous silicon to chemical and photocatalytic production of hydrogen

    International Nuclear Information System (INIS)

    Advantages of the use of silicon and porous silicon (PS) for the chemical production of hydrogen have been analyzed and compared with other fuels. An analytic expression is derived for the dependence of the volume of hydrogen produced at the PS interaction with water on the material porosity, as well as for the corresponding energy yield, when the produced gas is used in the power sources of electronic systems. It is found that the silicon porosity growth results in a reduction of the total volume of hydrogen released in the reaction with water, as compared with the amount of H2 obtained from the initial quantity of raw silicon. This effect is explained by significant losses of a material at PS formation. The ratio between the accumulation of hydrogen in the PS material and silicon losses in the etchant is determined to be optimal for the silicon porosity in the interval of 60-70%. When applying the produced hydrogen in fuel cells, the etching of silicon provides a growth of the output power, but reduces the total amount of the produced energy. Those mechanisms are analyzed to demonstrate the inexpedience of using the composites on the basis of pure nano-PS for the photocatalytic water dissociation

  13. Thermal Instability of Chemically Reacting Maxwell Fluid in a Horizontal Porous Layer with Constant Heat Flux Lower Boundary

    Directory of Open Access Journals (Sweden)

    Syeda Khudeja Akbar

    2015-08-01

    Full Text Available The effect of chemical reaction on the linear stability of a viscoelastic fluid saturated horizontal densely-packed porous layer is investigated. The viscoelastic properties are given by Maxwell constitutive relations. The porous layer is cooled from the upper boundary while an adiabatic thermal boundary condition is imposed at the lower boundary. Linear stability analysis suggests that there is a competition between the processes of viscous relaxation and thermal diffusion that causes the first convective instability to be oscillatory rather than stationary. The effect of Deborah number, Darcy-Prandtl number, normalized porosity, and the Frank-Kamenetskii number on the stability of the system is investigated. Using a weighted residual method we calculate numerically the convective thresholds for both stationary and oscillatory instability. The effects of viscoelasticity and chemical reaction on the instability are emphasized. Some existing results are reproduced as the particular cases of the present study.

  14. Unsteady MHD Mixed Convection Flow of Chemically Reacting Micropolar Fluid between Porous Parallel Plates with Soret and Dufour Effects

    OpenAIRE

    Odelu Ojjela; Naresh Kumar, N.

    2016-01-01

    The objective of the present study is to investigate the first-order chemical reaction and Soret and Dufour effects on an incompressible MHD combined free and forced convection heat and mass transfer of a micropolar fluid through a porous medium between two parallel plates. Assume that there are a periodic injection and suction at the lower and upper plates. The nonuniform temperature and concentration of the plates are assumed to be varying periodically with time. A suitable similarity trans...

  15. Tantalum coating on porous Ti6Al4V scaffold using chemical vapor deposition and preliminary biological evaluation

    International Nuclear Information System (INIS)

    Porous tantalum (Ta), produced via chemical vapor deposition (CVD) of commercially pure Ta onto a vitreous carbon, is currently available for use in orthopedic applications. However, the relatively high manufacturing cost and the incapability to produce customized implant using medical image data have limited its application to gain widespread acceptance. In this study, Ta film was deposited on porous Ti6Al4V scaffolds using CVD technique. Digital microscopy and scanning electron microscopy indicated that the Ta coating evenly covered the entire scaffold structure. X-ray diffraction analysis showed that the coating consisted of α and β phases of Ta. Goat mesenchymal stem cells were seeded and cultured on the Ti6Al4V scaffolds with and without coating. The tetrazolium-based colorimetric assay exhibited better cell adhesion and proliferation on Ta-coated scaffolds compared with uncoated scaffolds. The porous scaffolds were subsequently implanted in goats for 12 weeks. Histological analysis revealed similar bone formation around the periphery of the coated and uncoated implants, but bone ingrowth is better within the Ta-coated scaffolds. To demonstrate the ability of producing custom implant for clinical applications via this technology, we designed and fabricated a porous Ti6Al4V scaffold with segmental mandibular shape derived from patient computerized tomography data. - Highlights: • Ta film was coated on porous Ti6Al4V scaffold using chemical vapor deposition. Tantalum coating allowed for higher levels of cell adhesion and proliferation. • Better new bone formation occurred inside the tantalum-coated scaffolds. • Clinical image data was integrated with EBM to fabricate customized scaffold

  16. Up scaling two-phase flow in heterogeneous porous media; Mise a l'echelle des ecoulements diphasiques dans les milieux poreux heterogenes

    Energy Technology Data Exchange (ETDEWEB)

    Artus, V.

    2003-11-01

    For two-phase flow in heterogeneous media, the emergence of different flow regimes at large-scale is driven by local interactions between the viscous coupling and the heterogeneity. In particular, when the viscosity ratio is favorable, viscous effects induce a transverse flow that stabilizes the front while flooding. However, most of recent stochastic models neglect the influence of the viscous coupling. We developed a stochastic model for the dynamics of the front, taking the viscous coupling into account. For stable cases, this model relates the statistical properties of the front to the statistical properties of the permeability field. For stable flow in stratified media, we show that the front is stationary by parts in the reservoir. These parts can be identified as large-scale hydrodynamic layers and separately coarsened in the large-scale simulation model. For flows with favorable viscosity ratios in isotropic reservoirs, we show that a stationary front occurs, in a statistical sense. For unfavorable viscosity ratios, the flow is driven by the development of viscous fingering. These different regimes lead to different large-scale saturation profiles that can be matched with a macro-dispersion equation, if the effective convective flux is modified to take into account stabilizing or destabilizing viscous effects. (author)

  17. Chemical Imaging of Heterogeneous Muscle Foods Using Near-Infrared Hyperspectral Imaging in Transmission Mode.

    Science.gov (United States)

    Wold, Jens Petter; Kermit, Martin; Segtnan, Vegard Herman

    2016-06-01

    Foods and biomaterials are, in general, heterogeneous and it is often a challenge to obtain spectral data which are representative for the chemical composition and distribution. This paper presents a setup for near-infrared (NIR) transmission imaging where the samples are completely trans-illuminated, probing the entire sample. The system measures falling samples at high speed and consists of an NIR imaging scanner covering the spectral range 760-1040 nm and a powerful line light source. The investigated samples were rather big: whole pork bellies of thickness up to 5 cm, salmon fillets with skin, and 3 cm thick model samples of ground pork meat. Partial least square regression models for fat were developed for ground pork and salmon fillet with high correlations (R = 0.98 and R = 0.95, respectively). The regression models were applied at pixel level in the hyperspectral transmission images and resulted in images of fat distribution where also deeply embedded fat clearly contributed to the result. The results suggest that it is possible to use transmission imaging for rapid, nondestructive, and representative sampling of very heterogeneous foods. The proposed system is suitable for industrial use. PMID:27257302

  18. Tantalum coating on porous Ti6Al4V scaffold using chemical vapor deposition and preliminary biological evaluation.

    Science.gov (United States)

    Li, Xiang; Wang, Lin; Yu, Xiaoming; Feng, Yafei; Wang, Chengtao; Yang, Ke; Su, Daniel

    2013-07-01

    Porous tantalum (Ta), produced via chemical vapor deposition (CVD) of commercially pure Ta onto a vitreous carbon, is currently available for use in orthopedic applications. However, the relatively high manufacturing cost and the incapability to produce customized implant using medical image data have limited its application to gain widespread acceptance. In this study, Ta film was deposited on porous Ti6Al4V scaffolds using CVD technique. Digital microscopy and scanning electron microscopy indicated that the Ta coating evenly covered the entire scaffold structure. X-ray diffraction analysis showed that the coating consisted of α and β phases of Ta. Goat mesenchymal stem cells were seeded and cultured on the Ti6Al4V scaffolds with and without coating. The tetrazolium-based colorimetric assay exhibited better cell adhesion and proliferation on Ta-coated scaffolds compared with uncoated scaffolds. The porous scaffolds were subsequently implanted in goats for 12weeks. Histological analysis revealed similar bone formation around the periphery of the coated and uncoated implants, but bone ingrowth is better within the Ta-coated scaffolds. To demonstrate the ability of producing custom implant for clinical applications via this technology, we designed and fabricated a porous Ti6Al4V scaffold with segmental mandibular shape derived from patient computerized tomography data. PMID:23623123

  19. Effects of Chemical Reaction on Dissipative Radiative MHD Flow through a Porous Medium over a Nonisothermal Stretching Sheet

    Directory of Open Access Journals (Sweden)

    S. Mohammed Ibrahim

    2014-01-01

    Full Text Available The steady two-dimensional radiative MHD boundary layer flow of an incompressible, viscous, electrically conducting fluid caused by a nonisothermal linearly stretching sheet placed at the bottom of fluid saturated porous medium in the presence of viscous dissipation and chemical reaction is studied. The governing system of partial differential equations is converted to ordinary differential equations by using the similarity transformations, which are then solved by shooting method. The dimensionless velocity, temperature, and concentration are computed for different thermophysical parameters, namely, the magnetic parameter, permeability parameter, radiation parameter, wall temperature parameter, Prandtl number, Eckert number, Schmidt number, and chemical reaction.

  20. Chemical vapour etching-based porous silicon and grooving: Application in silicon solar cells processing

    Science.gov (United States)

    Ben Rabha, M.; Boujmil, M. F.; Saadoun, M.; Bessaïs, B.

    2005-06-01

    Sponge like porous silicon (PS) was formed by a simple and low cost chemical vapour etching (CVE) method and applied in polycrystalline silicon (mc-Si) solar cells processing. The CVE method consists of exposing Si wafers to HNO3/HF vapours. It was shown that 8 min of HNO3/HF CVE (volume ratio = 1/7) is sufficient to form optimized PS layers on the emitter of mc-Si cells. The CVE-based PS can simultaneously passivate the Si surface and serves as an effective antireflection coating (ARC). As a result, the reflectivity decreases by about 60% of its initial value and the internal quantum efficiency is improved, particularly in the short wavelength region. For acid vapours rich in HNO3 (HNO3/HF >1/4), the CVE method favours the formation of a (NH4)2SiF6 powder, which is highly soluble in water. These findings let us achieve anisotropic grooving that enables to groove mc-Si wafers locally and in depth using an adequate anti-acid mask. The CVE - based grooving technique was used to form buried metallic contacts on the rear and frontal surface of the Si wafer in order to improve the current collection in mc-Si solar cells. No alteration of the spectral response in the long wavelength range was observed in mc-Si cells with rear-buried contacts. Adjustments of theoretical spectral responses to experimental ones show an increase in the effective electron diffusion length (Ln), which was attributed to Al gettering (passivation) at grain boundaries and to the reduction of the effective thickness of the base of the cells.

  1. Chemical vapour etching-based porous silicon and grooving: Application in silicon solar cells processing

    Energy Technology Data Exchange (ETDEWEB)

    Ben Rabha, M.; Boujmil, M.F.; Saadoun, M.; Bessais, B. [Institut National de Recherche Scientifique et Technique, Laboratoire de Photovoltaique et des Semiconducteurs, BP 95, 2050 Hammam-Lif (Tunisia)

    2005-06-01

    Sponge like porous silicon (PS) was formed by a simple and low cost chemical vapour etching (CVE) method and applied in polycrystalline silicon (mc-Si) solar cells processing. The CVE method consists of exposing Si wafers to HNO{sub 3}/HF vapours. It was shown that 8 min of HNO{sub 3}/HF CVE (volume ratio = 1/7) is sufficient to form optimized PS layers on the emitter of mc-Si cells. The CVE-based PS can simultaneously passivate the Si surface and serves as an effective antireflection coating (ARC). As a result, the reflectivity decreases by about 60% of its initial value and the internal quantum efficiency is improved, particularly in the short wavelength region. For acid vapours rich in HNO{sub 3} (HNO{sub 3}/HF >1/4), the CVE method favours the formation of a (NH{sub 4}){sub 2}SiF{sub 6} powder, which is highly soluble in water. These findings let us achieve anisotropic grooving that enables to groove mc-Si wafers locally and in depth using an adequate anti-acid mask. The CVE - based grooving technique was used to form buried metallic contacts on the rear and frontal surface of the Si wafer in order to improve the current collection in mc-Si solar cells. No alteration of the spectral response in the long wavelength range was observed in mc-Si cells with rear-buried contacts. Adjustments of theoretical spectral responses to experimental ones show an increase in the effective electron diffusion length (Ln), which was attributed to Al gettering (passivation) at grain boundaries and to the reduction of the effective thickness of the base of the cells. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  2. Chemical and physicochemical characterization of porous hydroxyapatite ceramics made of natural bone.

    Science.gov (United States)

    Joschek, S; Nies, B; Krotz, R; Göferich, A

    2000-08-01

    The properties of a porous hydroxyapatite ceramic produced by sintering of bovine bone were investigated by using a number of physicochemical methods such as scanning electron microscopy (SEM), SEM in combination with energy dispersive X-ray spectroscopy (SEM-EDX), mercury intrusion porosimetry, krypton-adsorption, contact angle measurements, wide angle X-ray diffraction. Fourier transform infrared spectroscopy, thermal analysis, inductively coupled plasma optical atom emissions spectroscopy and flame atomic absorption spectroscopy. The results indicate that there are considerable differences between the ceramic and native bone. However, the most important properties with respect to the use of such ceramics as a biomaterial for filling bone defects namely the high porosity (> or = 57 +/- 2%) and the interconnecting pore system are maintained. While macropores with an average diameter of approx. 300 microm contribute 97% to porosity, micropores with an average diameter of 1.3 microm account for only 3% of the total porosity. The surface area was found to be approx. 0.1 m2/g. The contact angles of water (44.6 +/- 15.4 degrees, n = 5) and tetrahydrofurane (10 degrees) allow the processing of the ceramic to a drug carrier by incubation with aqueous or organic drug solutions. The ceramic is highly crystalline with crystal sizes of 1-7 microm and contains crystal bridges. The investigation of its chemical composition revealed small amounts of other inorganic compounds such as Ca4O(PO4)2, NaCaPO4, Ca3(PO4)2, CaO, and MgO. Besides trace amounts of aluminum, iron, magnesium, potassium, silica, sodium, vanadium and zinc it contains probably carbonated apatite. PMID:10905406

  3. Chemical vapour etching of silicon and porous silicon: silicon solar cells and micromachining applications

    Energy Technology Data Exchange (ETDEWEB)

    Ben Jaballah, A.; Hassen, M.; Hajji, M.; Saadoun, M.; Bessais, B.; Ezzaouia, H. [Institut National de Recherche Scientifique et Technique, Laboratoire de Photovoltaique et des Materiaux Semiconducteurs, PB 95 2050 Hammam lif (Tunisia)

    2005-06-01

    In this work, we used HNO{sub 3}/HF Vapour Etching (VE) of silicon (Si) wafers for the formation of different porous structures. Depending on the volume ratio of the HNO{sub 3}/HF acid mixture, we can obtain Porous Silicon (PS) layers or a (NH{sub 4}){sub 2}SiF{sub 6} like powder phase. These two kind of porous structures may be used in silicon solar cells and in micromachining applications. The VE technique allows producing thick porous layers (>100 {mu}m) in short times. Simple masking films enable to selectively groove Si wafers, leading to the formation of holes and channels of different sizes suitable for their application in micromachining. The various grooving profiles were investigated by Scanning electron microscopy (SEM). (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  4. Highly Porous Carbon Materials from Biomass by Chemical and Carbonization Method: A Comparison Study

    OpenAIRE

    Wan Nor Roslam Wan Isahak; Mohamed Wahab Mahamed Hisham; Mohd Ambar Yarmo

    2013-01-01

    Porous carbon obtained by dehydrating agent, concentrated sulfuric acid (H2SO4), from biomass containing high cellulose (filter paper (FP), bamboo waste, and empty fruit bunches (EFB)) shows very high surface area and better thermal behavior. At room temperature (without heating), treatment of H2SO4 removed all the water molecules in the biomass and left the porous carbon without emitting any gaseous byproducts. Brunauer-Emmett-Teller (BET) surface analysis has shown that bamboo-based carbon ...

  5. Taylor dispersion in heterogeneous porous media: Extended method of moments, theory, and modelling with two-relaxation-times lattice Boltzmann scheme

    Science.gov (United States)

    Vikhansky, Alexander; Ginzburg, Irina

    2014-02-01

    This article describes a generalization of the method of moments, called extended method of moments (EMM), for dispersion in periodic structures composed of impermeable or permeable porous inclusions. Prescribing pre-computed steady state velocity field in a single periodic cell, the EMM sequentially solves specific linear stationary advection-diffusion equations and restores any-order moments of the resident time distribution or the averaged concentration distribution. Like the pioneering Brenner's method, the EMM recovers mean seepage velocity and Taylor dispersion coefficient as the first two terms of the perturbative expansion. We consider two types of dispersion: spatial dispersion, i.e., spread of initially narrow pulse of concentration, and temporal dispersion, where different portions of the solute have different residence times inside the system. While the first (mean velocity) and the second (Taylor dispersion coefficient) moments coincide for both problems, the higher moments are different. Our perturbative approach allows to link them through simple analytical expressions. Although the relative importance of the higher moments decays downstream, they manifest the non-Gaussian behaviour of the breakthrough curves, especially if the solute can diffuse into less porous phase. The EMM quantifies two principal effects of bi-modality, as the appearance of sharp peaks and elongated tails of the distributions. In addition, the moments can be used for the numerical reconstruction of the corresponding distribution, avoiding time-consuming computations of solute transition through heterogeneous media. As illustration, solutions for Taylor dispersion, skewness, and kurtosis in Poiseuille flow and open/impermeable stratified systems, both in rectangular and cylindrical channels, power-law duct flows, shallow channels, and Darcy flow in parallel porous layers are obtained in closed analytical form for the entire range of Péclet numbers. The high-order moments and

  6. Effect of Alkali-Acid-Heat Chemical Surface Treatment on Electron Beam Melted Porous Titanium and Its Apatite Forming Ability

    Directory of Open Access Journals (Sweden)

    Suzan Bsat

    2015-04-01

    Full Text Available Advanced additive manufacturing techniques such as electron beam melting (EBM, can produce highly porous structures that resemble the mechanical properties and structure of native bone. However, for orthopaedic applications, such as joint prostheses or bone substitution, the surface must also be bio-functionalized to promote bone growth. In the current work, EBM porous Ti6Al4V alloy was exposed to an alkali acid heat (AlAcH treatment to bio-functionalize the surface of the porous structure. Various molar concentrations (3, 5, 10M and immersion times (6, 24 h of the alkali treatment were used to determine optimal parameters. The apatite forming ability of the samples was evaluated using simulated body fluid (SBF immersion testing. The micro-topography and surface chemistry of AlAcH treated samples were evaluated before and after SBF testing using scanning electron microscopy and energy dispersive X-ray spectroscopy. The AlAcH treatment successfully modified the topographical and chemical characteristics of EBM porous titanium surface creating nano-topographical features ranging from 200–300 nm in size with a titania layer ideal for apatite formation. After 1 and 3 week immersion in SBF, there was no Ca or P present on the surface of as manufactured porous titanium while both elements were present on all AlAcH treated samples except those exposed to 3M, 6 h alkali treatment. An increase in molar concentration and/or immersion time of alkali treatment resulted in an increase in the number of nano-topographical features per unit area as well as the amount of titania on the surface.

  7. Influences of Flow Transients and Porous Medium Heterogeneity on Colloid-Associated Contaminant Transport in the Vadose Zone

    International Nuclear Information System (INIS)

    Radionuclides, metals, and dense non-aqueous phase liquids have contaminated about six billion cubic meters of soil at Department of Energy (DOE) sites. The subsurface transport of many of these contaminants is facilitated by colloids (i.e., microscopic, waterborne particles). The first step in the transport of contaminants from their sources to off-site surface water and groundwater is migration through the vadose zone. Developing our understanding of the migration of colloids and colloid-associated contaminants through the vadose zone is critical to assessing and controlling the release of contaminants from DOE sites. In this study, we examined the mobilization, transport, and filtration (retention) of mineral colloids and colloid-associated radionuclides within unsaturated porous media. This investigation involved laboratory column experiments designed to identify properties that affect colloid mobilization and retention and pore-scale visualization experiments designed to elucidate mechanisms that govern these colloid-mass transfer processes. The experiments on colloid mobilization and retention were supplemented with experiments on radionuclide transport through porous media and on radionuclide adsorption to mineral colloids. Observations from all of these experiments--the column and visualization experiments with colloids and the experiments with radionuclides--were used to guide the development of mathematical models appropriate for describing colloids and colloid-facilitated radionuclide transport through the vadose zone

  8. Probing Seismically Melting Induced Mantle Heterogeneities in Thermal-chemical Convection Models

    Science.gov (United States)

    Heck, H. V.; Davies, H.; Nowacki, A.; Wookey, J. M.

    2015-12-01

    Two regions at the base of the Earth's mantle (the Large Low-Shear Velocity Provinces) pose a fundamental problem in understanding large-scale mantle dynamics and history. Are they dense piles of (possibly primordial) material separated from mantle circulation, or large-scale thermal features which are part of global mantle convection? Or some combination of the two? We use our numerical 3D spherical mantle convection code to perform simulations of the Earths mantle dynamical evolution. We drive the surface velocity of the model according to 200 Ma plate motion reconstructions, to arrive at Earth-like structures in the mantle at present day. Variations in bulk chemistry will be tracked in two ways: 1) by starting the calculations with a (primordial) dense layer at the base of the mantle, and 2) by tracking basalt fraction which is fractionated upon melting close to the surface. The resulting distribution of chemical heterogeneity and temperature will be converted to seismic velocities. This will be done with a thermodynamical database (Stixrude & Lithgow-Bertelloni, GJI, 2005, 2011), allowing us to compare the model with previous observations of triplications and waveform complexity near the margins of the LLSVPs. These observations have been taken as proof that strong chemical variations are present; our simulations can be used to show whether this is true, or if purely thermal convection can also cause these features. We simulate finite-frequency, 3D seismograms at ~5 s period and compare these with previous studies.

  9. Modelling of the solidification process and the chemical heterogeneity of a 26NiCrMov115 steel ingot

    OpenAIRE

    Balcar, Martin; Železný, Rudolf; Martínek, Ludvík; Fila, Pavel; Bažan, Jiří

    2007-01-01

    Steel making at ŽĎAS, a.s. using secondary metallurgy technology makes it possible to produce liquid metal with high levels of metallurgical cleanliness. During the casting and subsequent cooling of forging ingots, the steel solidification takes place. Directional material solidification, grain size, chemical heterogeneity and discontinuities can have a negative effect on the products’ final properties. The comparison of the chemical composition based on a numerical calculation with ...

  10. Preparation of highly porous carbonaceous sorbents from sewage sludge by physical and chemical activation

    Energy Technology Data Exchange (ETDEWEB)

    Ros, A.; Martin, M.J. [Girona Univ., Lab. d' Enginyerie Quimica i Ambiental, Dept. d' Enginyeria Quimica, Agraria i Tecnologia Agroalimentaria, Facultat de Ciencies (Spain); Lillo-Rodenas, M.A.; Linares-Solano, A. [Alicante Univ., Dept. de Quimica Inorganica (Spain); Fuente, E.; Montes-Moran, M.A. [Instituto Nacional del Carbon, CSIC, Oviedo (Spain)

    2005-07-01

    Among the different porous materials, activated carbon (AC) is the most widely used for environmental applications such as gas-phase pollutant removal, gas separation, solvent recovery and water purification, because of its high specific surfacea. Commercial activated carbons are generally produced from coals and lignocellulosic materials [1]. Additionally, in the latest years great attention is being focused on the reuse of wastes such as sewage sludges [2,3]. The objective of this study is to find more effective activating procedures to prepare AC from sewage sludge. Both dried sludges from two different WWTP (SL, SB) and their corresponding chars prepared by pyrolysis (SL-P, SB-P) were activated using physical activation (CO{sub 2}) and chemical activation (H{sub 3}PO{sub 4}, NaOH and KOH). As shown in Table 1, pyrolysis of the raw sludges slightly increased the specific surface area, up to 50 m{sup 2}/g. Acid-washing of the pyrolyzed samples with 5 M HCl removes part of the metal content leading to an increase in the specific surface areas for both SL-PD and SB-PD, with surface areas of 428 m{sup 2}/g and 188 m{sup 2}/g, respectively. This simple washing treatment is useful for the development of porous adsorbents, especially in the case of SL derived materials. Our results show that CO{sub 2} physical activation of the pyrolyzed and the HCl-washed samples develops no appreciable porosity in the final materials, under the experimental conditions used. For CO{sub 2} activation, maximum temperatures of 870 C and holding times up to 4 hours in CO{sub 2} (100 ml/min) were used. Chemical activation with H{sub 3}PO{sub 4} of the pristine samples and those pyrolyzed was performed at 450 C, a temperature typically used for the activation by H{sub 3}PO{sub 4} of lignocellulosic precursors, and using two different H{sub 3}PO{sub 4} solutions (30 and 50% wt). These conditions were not either suitable for an efficient porosity development. A detailed study about the

  11. A note on conservative transport in anisotropic, heterogeneous porous media in the presence of small-amplitude transients

    Science.gov (United States)

    Naff, R.L.

    1998-01-01

    The late-time macrodispersion coefficients are obtained for the case of flow in the presence of a small-scale deterministic transient in a three-dimensional anisotropic, heterogeneous medium. The transient is assumed to affect only the velocity component transverse to the mean flow direction and to take the form of a periodic function. For the case of a highly stratified medium, these late-time macrodispersion coefficients behave largely as the standard coefficients used in the transport equation. Only in the event that the medium is isotropic is it probable that significant deviations from the standard coefficients would occur.

  12. Spectroscopic Characterization and Simulation of Chemical Sputtering Using the DiMES Porous Plug Injector in DIII-D

    Energy Technology Data Exchange (ETDEWEB)

    McLean, A G; Davis, J W; Stangeby, P C; Brooks, N H; Whyte, D G; Allen, S L; Bray, B D; Brezinsek, S; Elder, J D; Fenstermacher, M E; Groth, M; Haasz, A A; Hollmann, E M; Isler, R; Lasnier, C J; Rudakov, D L; Watkins, J G; West, W P; Wong, C C

    2006-05-15

    A self-contained gas injection system for the Divertor Material Evaluation System (DiMES) on DIII-D has been employed for in-situ study of chemical erosion in the tokamak divertor environment. The Porous Plug Injector (PPI) releases methane, a major component of molecular influx due to chemical sputtering of graphite, from the tile surface into the plasma at a controlled rate through a porous graphite surface. Perturbation to local plasma is minimized, while also simulating the immediate environment of methane molecules released from a solid graphite surface. The release rate was chosen to be of the same order of magnitude as natural sputtering. Photon efficiencies of CH{sub 4} for measured local plasma conditions are reported. The contribution of chemical versus physical sputtering to the source of C{sup +} at the target is assessed through measurement of CII and CD/CH band emissions during release of CH{sub 4} from the PPI, and due to intrinsic emission.

  13. Porous polymer film calcium ion chemical sensor and method of using the same

    Science.gov (United States)

    Porter, M.D.; Chau, L.K.

    1991-02-12

    A method of measuring calcium ions is disclosed wherein a calcium sensitive reagent, calcichrome, is immobilized on a porous polymer film. The reaction of the calcium sensitive reagent to the Ca(II) is then measured and concentration determined as a function of the reaction. 1 figure.

  14. Association between occupational exposures to pesticides with heterogeneous chemical structures and farmer health in China

    Science.gov (United States)

    Huang, Xusheng; Zhang, Chao; Hu, Ruifa; Li, Yifan; Yin, Yanhong; Chen, Zhaohui; Cai, Jinyang; Cui, Fang

    2016-01-01

    This study analyzed the associations of farmers’ exposure to organophosphates (OPs), organosulfurs (OSs), organonitrogens (ONs) and pyrethroids (PYRs) with parameters of the blood complete counts (CBC), a blood chemistry panel (BCP) and the conventional nerve conduction studies among 224 farmers in China in 2012. Two health examinations and a series of follow-up field surveys were conducted. Multiple linear regression analyses were used to evaluate the associations. The results show considerable associations between multiple groups of pesticides and several CBC parameters, but it was not enough to provide evidence of hematological disorders. The short- and medium-term OPs exposures were mainly associated with liver damage and peripheral nerve impairment, respectively, while OSs exposure might induce liver damage and renal dysfunction. The neurotoxicity of ONs was second only to OPs in addition to its potential liver damage and the induced alterations in glucose. In comparison, the estimated results show that PYRs would be the least toxic in terms of the low-dose application. In conclusion, occupational exposures to pesticides with heterogeneous chemical structures are associated with farmer health in different patterns, and the association between a specific group of pesticides and farmer health also differs between the short- and medium-term exposures. PMID:27117655

  15. An $h$-Adaptive Operator Splitting Method for Two-Phase Flow in 3D Heterogeneous Porous Media

    KAUST Repository

    Chueh, Chih-Che

    2013-01-01

    The simulation of multiphase flow in porous media is a ubiquitous problem in a wide variety of fields, such as fuel cell modeling, oil reservoir simulation, magma dynamics, and tumor modeling. However, it is computationally expensive. This paper presents an interconnected set of algorithms which we show can accelerate computations by more than two orders of magnitude compared to traditional techniques, yet retains the high accuracy necessary for practical applications. Specifically, we base our approach on a new adaptive operator splitting technique driven by an a posteriori criterion to separate the flow from the transport equations, adaptive meshing to reduce the size of the discretized problem, efficient block preconditioned solver techniques for fast solution of the discrete equations, and a recently developed artificial diffusion strategy to stabilize the numerical solution of the transport equation. We demonstrate the accuracy and efficiency of our approach using numerical experiments in one, two, and three dimensions using a program that is made available as part of a large open source library. © 2013 Society for Industrial and Applied Mathematics.

  16. Correspondence Between One- and Two-Equation Models for Solute Transport in Two-Region Heterogeneous Porous Media

    KAUST Repository

    Davit, Y.

    2012-07-26

    In this work, we study the transient behavior of homogenized models for solute transport in two-region porous media. We focus on the following three models: (1) a time non-local, two-equation model (2eq-nlt). This model does not rely on time constraints and, therefore, is particularly useful in the short-time regime, when the timescale of interest (t) is smaller than the characteristic time (τ 1) for the relaxation of the effective macroscale parameters (i. e., when t ≤ τ 1); (2) a time local, two-equation model (2eq). This model can be adopted when (t) is significantly larger than (τ 1) (i.e., when t≫τ 1); and (3) a one-equation, time-asymptotic formulation (1eq ∞). This model can be adopted when (t) is significantly larger than the timescale (τ 2) associated with exchange processes between the two regions (i. e., when t≫τ 2). In order to obtain insight into this transient behavior, we combine a theoretical approach based on the analysis of spatial moments with numerical and analytical results in several simple cases. The main result of this paper is to show that there is only a weak asymptotic convergence of the solution of (2eq) towards the solution of (1eq ∞) in terms of standardized moments but, interestingly, not in terms of centered moments. The physical interpretation of this result is that deviations from the Fickian situation persist in the limit of long times but that the spreading of the solute is eventually dominating these higher order effects. © 2012 Springer Science+Business Media B.V.

  17. Spectroscopic characterization and simulation of chemical sputtering using the DiMES porous plug injector in DIII-D

    Energy Technology Data Exchange (ETDEWEB)

    McLean, A.G. [University of Toronto, Institute for Aerospace Studies, 4925 Dufferin Street, Toronto, Ont., M3H 5T6 (Canada)]. E-mail: adam.mclean@utoronto.ca; Davis, J.W. [University of Toronto, Institute for Aerospace Studies, 4925 Dufferin Street, Toronto, Ont., M3H 5T6 (Canada); Stangeby, P.C. [University of Toronto, Institute for Aerospace Studies, 4925 Dufferin Street, Toronto, Ont., M3H 5T6 (Canada); Brooks, N.H. [General Atomics, San Diego, CA 92186-5608 (United States); Whyte, D.G. [M.I.T. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge MA 02139 (United States); Allen, S.L. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Bray, B.D. [General Atomics, San Diego, CA 92186-5608 (United States); Brezinsek, S. [Institut fuer Plasmaphysik Forschungszentrum, Juelich GmbH 52425, Juelich (Germany); Elder, J.D. [University of Toronto, Institute for Aerospace Studies, 4925 Dufferin Street, Toronto, Ont., M3H 5T6 (Canada); Fenstermacher, M.E. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Groth, M. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Haasz, A.A. [University of Toronto, Institute for Aerospace Studies, 4925 Dufferin Street, Toronto, Ont., Canada M3H 5T6 (Canada); Hollmann, E.M. [University of California, San Diego, La Jolla, CA 92093 (United States); Isler, R.C. [Oak Ridge National Laboratory, Oak Ridge, TN 37831 (United States); Lasnier, C.J. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Rudakov, D.L. [University of California, San Diego, La Jolla, CA 92093 (United States); Watkins, J.G. [Sandia National Laboratories, Albuquerque, NM 87185 (United States); West, W.P. [General Atomics, San Diego, CA 92186-5608 (United States); Wong, C.P.C. [General Atomics, San Diego, CA 92186-5608 (United States)

    2007-06-15

    A self-contained gas injection system for the Divertor Material Evaluation System (DiMES) on DIII-D has been employed for in situ study of chemical erosion in the tokamak divertor environment. The porous plug injector (PPI) releases methane into the plasma at a controlled rate through a porous graphite surface flush to a tile. In this way, the perturbation to the local plasma can be minimized, while also simulating the immediate environment of methane molecules released from a solid graphite surface. Photon efficiencies of CH{sub 4} for measured local plasma conditions are reported. The contribution of chemical vs physical sputtering to the source of C{sup +} at the target can, in principle, be assessed through measurement of CII and CD/CH band emissions during release of CH{sub 4} from the PPI, and due to intrinsic emission. These first results from this new experimental tool demonstrate the potential for the PPI to provide definitive results in future applications in DIII-D and indicate the improvements required to obtain firm quantitative conclusions.

  18. Spectroscopic characterization and simulation of chemical sputtering using the DiMES porous plug injector in DIII-D

    International Nuclear Information System (INIS)

    A self-contained gas injection system for the Divertor Material Evaluation System (DiMES) on DIII-D has been employed for in situ study of chemical erosion in the tokamak divertor environment. The porous plug injector (PPI) releases methane into the plasma at a controlled rate through a porous graphite surface flush to a tile. In this way, the perturbation to the local plasma can be minimized, while also simulating the immediate environment of methane molecules released from a solid graphite surface. Photon efficiencies of CH4 for measured local plasma conditions are reported. The contribution of chemical vs physical sputtering to the source of C+ at the target can, in principle, be assessed through measurement of CII and CD/CH band emissions during release of CH4 from the PPI, and due to intrinsic emission. These first results from this new experimental tool demonstrate the potential for the PPI to provide definitive results in future applications in DIII-D and indicate the improvements required to obtain firm quantitative conclusions

  19. Effects of Radiation and Chemical Reaction on MHD Free Convection Flow past a Vertical Plate in the Porous Medium

    Directory of Open Access Journals (Sweden)

    S. Mondal

    2014-12-01

    Full Text Available The objective is to study the effects of thermal radiation and chemical reaction on mass transfer on unsteady free convection flow past an exponentially accelerated infinite vertical plate through porous medium in the presence of magnetic field. The fluid is considered here as absorbing/emitting radiation but a non-scattering medium. The plate temperature is raised linearly with time and the concentration level near the plate is raised to C   . We use proper transformations to make the governing equations dimensionless. The dimensionless governing equations are reduced to a set of ordinary differential equations. Then we solve these equations with the help of transformed boundary conditions. The effect of various parameters such as Grashof number, Modified Grashof number, Schmidt number, Prandtl number, Magnetic parameter, time, accelerating parameter, Dimensionless porous medium factor and Dimensionless chemical reaction parameter on velocity profiles, temperature profiles, concentration profiles, skin friction profiles, rate of heat transfer profiles and rate of mass transfer profiles are shown graphically

  20. Unsteady MHD Mixed Convection Flow of Chemically Reacting Micropolar Fluid between Porous Parallel Plates with Soret and Dufour Effects

    Directory of Open Access Journals (Sweden)

    Odelu Ojjela

    2016-01-01

    Full Text Available The objective of the present study is to investigate the first-order chemical reaction and Soret and Dufour effects on an incompressible MHD combined free and forced convection heat and mass transfer of a micropolar fluid through a porous medium between two parallel plates. Assume that there are a periodic injection and suction at the lower and upper plates. The nonuniform temperature and concentration of the plates are assumed to be varying periodically with time. A suitable similarity transformation is used to reduce the governing partial differential equations into nonlinear ordinary differential equations and then solved numerically by the quasilinearization method. The fluid flow and heat and mass transfer characteristics for various parameters are analyzed in detail and shown in the form of graphs. It is observed that the concentration of the fluid decreases whereas the temperature of the fluid enhances with the increasing of chemical reaction and Soret and Dufour parameters.

  1. Porous solgel fiber as a transducer for highly sensitive chemical sensing.

    Science.gov (United States)

    Tao, Shiquan; Winstead, Christopher B; Singh, Jagdish P; Jindal, Rajeev

    2002-08-15

    A novel solgel process for making porous silica fiber and doping the fiber core with sensing material is described. A CoCl(2) -doped solgel fiber was fabricated and was used to construct an active-core optical fiber moisture sensor. Test results show that the sensitivity of the active-core optical fiber sensor is much higher than that of an evanescent-wave-based optical fiber sensor. PMID:18026453

  2. Heat and Moisture Transport in Unsaturated Porous Media -- A Coupled Model in Terms of Chemical Potential

    OpenAIRE

    Sullivan, Eric

    2013-01-01

    Transport phenomena in porous media are commonplace in our daily lives. Examples and applications include heat and moisture transport in soils, baking and drying of food stuffs, curing of cement, and evaporation of fuels in wild fires. Of particular interest to this study are heat and moisture transport in unsaturated soils. Historically, mathematical models for these processes are derived by coupling classical Darcy's, Fourier's, and Fick's laws with volume averaged conservation of mass and ...

  3. Kinetic study of the heterogeneous photocatalysis of porous nanocrystalline TiO₂ assemblies using a continuous random walk simulation.

    Science.gov (United States)

    Liu, Baoshun; Zhao, Xiujian

    2014-10-28

    The continuous time random walk (CTRW) simulation was used to study the photocatalytic kinetics of nanocrystalline (nc)-TiO2 assemblies in this research. nc-TiO2 assemblies, such as nc-TiO2 porous films and nc-TiO2 hierarchical structures, are now widely used in photocatalysis. The nc-TiO2 assemblies have quasi-disordered networks consisting of many tiny nanoparticles, so the charge transport within them can be studied by CTRW simulation. We considered the experimental facts that the holes can be quickly trapped and transferred to organic species just after photogeneration, and the electrons transfer to O2 slowly and accumulate in the conduction band of TiO2, which is believed to be the rate-limiting process of the photocatalysis under low light intensity and low organic concentration. Due to the existence of numerous traps, the electron transport within the nc-TiO2 assemblies follows a multi-trapping (MT) mechanism, which significantly limits the electron diffusion speed. The electrons need to undergo several steps of MT transport before transferring to oxygen, so it is highly important that the electron transport in nc-TiO2 networks is determined for standard photocatalytic reactions. Based on the MT transport model, the transient decays of photocurrents during the photocatalytic oxidation of formic acid were studied by CTRW simulation, and are in good accordance with experiments. The steady state photocatalysis was also simulated. The effects of organic concentration, light intensity, temperature, and nc-TiO2 crystallinity on the photocatalytic kinetics were investigated, and were also consistent with the experimental results. Due to the agreement between the simulation and the experiments for both the transient and the steady state photocatalysis, the MT charge transport should be an important mechanism that controls the kinetics of recombination and photocatalysis in nc-TiO2 assemblies. Also, our research provides a new methodology to study the photocatalytic

  4. Chemical reactivity of {alpha}-isosaccharinic acid in heterogeneous alkaline systems

    Energy Technology Data Exchange (ETDEWEB)

    Glaus, M. A.; Loon, L. R. Van

    2008-11-15

    Cellulose degradation under alkaline conditions is of relevance for the mobility of many radionuclides in the near-field of a cementitious repository for radioactive waste, because metal-binding degradation products may be formed. Among these, {alpha}-isosaccharinic acid ({alpha}-ISA) is the strongest complexant. The prediction of the equilibrium concentration of {alpha}-ISA in cement pore water is therefore an important step in the assessment of the influence of cellulose degradation products on the speciation of radionuclides in such environments. The present report focuses on possible chemical transformation reactions of {alpha}-ISA in heterogeneous alkaline model systems containing either Ca(OH){sub 2} or crushed hardened cement paste. The transformation reactions were monitored by measuring the concentration of {alpha}-ISA by high performance anion exchange chromatography and the formation of reaction products by high performance ion exclusion chromatography. The overall loss of organic species from solution was monitored by measuring the concentration of non-purgeable organic carbon. The reactions were examined in diluted and compacted suspensions, either at 25 {sup o}C or 90 {sup o}C, and under anaerobic atmospheres obtained by various methods. It was found that {alpha}-ISA was transformed under all conditions tested to some extent. Reaction products, such as glycolate, formate, lactate and acetate, all compounds with less complexing strength than {alpha}-ISA, were detected. The amount of reaction products identified by the chromatographic technique applied was {approx}50 % of the amount of {alpha}-ISA reacted. Sorption of {alpha}-ISA to Ca(OH){sub 2} contributed only to a minor extent to the loss of {alpha}-ISA from the solution phase. As the most important conclusion of the present work it was demonstrated that the presence of oxidising agents had a distinctive influence on the turnover of {alpha}-ISA. Under aerobic conditions {alpha}-ISA was

  5. Chemical reactivity of {alpha}-isosaccharinic acid in heterogeneous alkaline systems

    Energy Technology Data Exchange (ETDEWEB)

    Glaus, M. A.; Loon, L. R. Van

    2009-05-15

    Cellulose degradation under alkaline conditions is of relevance for the mobility of many radionuclides in the near-field of a cementitious repository for radioactive waste, because metal-binding degradation products may be formed. Among these, {alpha}- isosaccharinic acid ({alpha}-ISA) is the strongest complexant. The prediction of the equilibrium concentration of {alpha}-ISA in cement pore water is therefore an important step in the assessment of the influence of cellulose degradation products on the speciation of radionuclides in such environments. The present report focuses on possible chemical transformation reactions of {alpha}-ISA in heterogeneous alkaline model systems containing either Ca(OH){sub 2} or crushed hardened cement paste. The transformation reactions were monitored by measuring the concentration of {alpha}-ISA by high performance anion exchange chromatography and the formation of reaction products by high performance ion exclusion chromatography. The overall loss of organic species from solution was monitored by measuring the concentration of non-purgeable organic carbon. The reactions were examined in diluted and compacted suspensions, at either 25 {sup o}C or 90 {sup o}C, and under anaerobic atmospheres obtained by various methods. It was found that {alpha}-ISA was transformed under all conditions tested to some extent. Reaction products, such as glycolate, formate, lactate and acetate, all compounds with less complexing strength than {alpha}-ISA, were detected. The amount of reaction products identified by the chromatographic technique applied was {approx} 50 % of the amount of {alpha}-ISA reacted. Sorption of {alpha}-ISA to Ca(OH){sub 2} contributed only to a minor extent to the loss of {alpha}-ISA from the solution phase. As the most important conclusion of the present work it was demonstrated that the presence of oxidising agents had a distinctive influence on the turnover of {alpha}-ISA. Under aerobic conditions {alpha}-ISA was

  6. Chemical reactivity of α-isosaccharinic acid in heterogeneous alkaline systems

    International Nuclear Information System (INIS)

    Cellulose degradation under alkaline conditions is of relevance for the mobility of many radionuclides in the near-field of a cementitious repository for radioactive waste, because metal-binding degradation products may be formed. Among these, α- isosaccharinic acid (α-ISA) is the strongest complexant. The prediction of the equilibrium concentration of α-ISA in cement pore water is therefore an important step in the assessment of the influence of cellulose degradation products on the speciation of radionuclides in such environments. The present report focuses on possible chemical transformation reactions of α-ISA in heterogeneous alkaline model systems containing either Ca(OH)2 or crushed hardened cement paste. The transformation reactions were monitored by measuring the concentration of α-ISA by high performance anion exchange chromatography and the formation of reaction products by high performance ion exclusion chromatography. The overall loss of organic species from solution was monitored by measuring the concentration of non-purgeable organic carbon. The reactions were examined in diluted and compacted suspensions, at either 25 oC or 90 oC, and under anaerobic atmospheres obtained by various methods. It was found that α-ISA was transformed under all conditions tested to some extent. Reaction products, such as glycolate, formate, lactate and acetate, all compounds with less complexing strength than α-ISA, were detected. The amount of reaction products identified by the chromatographic technique applied was ∼ 50 % of the amount of α-ISA reacted. Sorption of α-ISA to Ca(OH)2 contributed only to a minor extent to the loss of α-ISA from the solution phase. As the most important conclusion of the present work it was demonstrated that the presence of oxidising agents had a distinctive influence on the turnover of α-ISA. Under aerobic conditions α-ISA was quantitatively converted to reaction products, whereas under strict anaerobic conditions, only small

  7. Chemical reactivity of α-isosaccharinic acid in heterogeneous alkaline systems

    International Nuclear Information System (INIS)

    Cellulose degradation under alkaline conditions is of relevance for the mobility of many radionuclides in the near-field of a cementitious repository for radioactive waste, because metal-binding degradation products may be formed. Among these, α-isosaccharinic acid (α-ISA) is the strongest complexant. The prediction of the equilibrium concentration of α-ISA in cement pore water is therefore an important step in the assessment of the influence of cellulose degradation products on the speciation of radionuclides in such environments. The present report focuses on possible chemical transformation reactions of α-ISA in heterogeneous alkaline model systems containing either Ca(OH)2 or crushed hardened cement paste. The transformation reactions were monitored by measuring the concentration of α-ISA by high performance anion exchange chromatography and the formation of reaction products by high performance ion exclusion chromatography. The overall loss of organic species from solution was monitored by measuring the concentration of non-purgeable organic carbon. The reactions were examined in diluted and compacted suspensions, either at 25 oC or 90 oC, and under anaerobic atmospheres obtained by various methods. It was found that α-ISA was transformed under all conditions tested to some extent. Reaction products, such as glycolate, formate, lactate and acetate, all compounds with less complexing strength than α-ISA, were detected. The amount of reaction products identified by the chromatographic technique applied was ∼50 % of the amount of α-ISA reacted. Sorption of α-ISA to Ca(OH)2 contributed only to a minor extent to the loss of α-ISA from the solution phase. As the most important conclusion of the present work it was demonstrated that the presence of oxidising agents had a distinctive influence on the turnover of α-ISA. Under aerobic conditions α-ISA was quantitatively converted to reaction products, whereas under strict anaerobic conditions, only small

  8. Variable viscosity and thermophoresis effects on Darcy mixed convective heat and mass transfer past a porous wedge in the presence of chemical reaction

    Directory of Open Access Journals (Sweden)

    Muhaimin I.

    2009-01-01

    Full Text Available An analysis is presented to investigate the effect of thermophoresis particle deposition and variable viscosity on Darcy mixed convective heat and mass transfer of a viscous, incompressible fluid past a porous wedge in the presence of chemical reaction. The wall of the wedge is embedded in a uniform Darcian porous medium in order to allow for possible fluid wall suction or injection. The viscosity of the fluid is assumed to be a inverse linear function of temperature. The results are analyzed for the effect of different physical parameters, such as variable viscosity, magnetic, chemical reaction and thermophoresis parameters, on the flow, the heat and mass transfer characteristics.

  9. Optical chemical sensors for atmospheric pollutants based on nano porous materials: application to the formaldehyde and the other carbonyl compounds

    International Nuclear Information System (INIS)

    Formaldehyde, a well-identified indoor pollutant, was recently classified as carcinogenic. New regulations for the air quality are expected and therefore there is a need for low-cost sensors, sensitive and selective with a fast response time for the detection of formaldehyde at ppb level. In the present work, we had developed a chemical sensor based on nano-porous matrices doped with Fluoral-P and optical methods of detection. The nano-porous matrices, elaborated via the Sol-Gel process, display nano-pores whose cavity is tailored for the trapping of the targeted pollutant. They provide a first selectivity with the discrimination of the pollutants by their size. A second selectivity is obtained with a molecular probe, Fluoral-P, which reacts specifically with formaldehyde leading to the 3,5- di-acetyl-1,4-dihydro-lutidine (DDL). The kinetics of formation of DDL was studied as function of many parameters such as the concentration of Fluoral-P in the matrix, the pollutant content in gas mixture, the flow rate, the relative humidity of the gas mixtures and interference with other carbonylated compounds. The present chemical sensor can detect, via absorbance measurements, 2 ppb of formaldehyde within 30 min over a O to 60% relative humidity range. Moreover, to detect the total carbonylated compounds, we also explored the potentiality of a chemical sensor using, as a probe molecule, the 2'4-dinitro-phenyl-hydrazine which forms with these compounds the corresponding hydrazones derivatives. A patent was deposited for these two sensors. We have also developed a semi-miniaturized prototype for demonstration, using a flow cell, a miniaturized spectrophotometer, a light source and a lap-top. (author)

  10. Radiation-chemical behavior of uranium and plutonium in heterogeneous MeO2-aqueous solution systems

    International Nuclear Information System (INIS)

    The paper studies radiation-chemical behavior of U and Pu in heterogeneous UO2-aqueous mellitate systems and the PuO2-groundwater systems, respectively. It is found that U(IV) passes into the aqueous phase in the irradiated system and oxidizes further to U(VI) while Pu(IV) solubilizes both in irradiated and unirradiated groundwater and then goes to Pu(V) and Pu(III). The latter processes is more powerful in irradiated solutions. The radiation-chemical behavior of U and Pu in the systems under study is interpreted on the strength of spectrophotometric characteristics of irradiated and unirradiated solutions. (author)

  11. Analysis and improvement of Brinkman lattice Boltzmann schemes: Bulk, boundary, interface. Similarity and distinctness with finite elements in heterogeneous porous media

    Science.gov (United States)

    Ginzburg, Irina; Silva, Goncalo; Talon, Laurent

    2015-02-01

    This work focuses on the numerical solution of the Stokes-Brinkman equation for a voxel-type porous-media grid, resolved by one to eight spacings per permeability contrast of 1 to 10 orders in magnitude. It is first analytically demonstrated that the lattice Boltzmann method (LBM) and the linear-finite-element method (FEM) both suffer from the viscosity correction induced by the linear variation of the resistance with the velocity. This numerical artefact may lead to an apparent negative viscosity in low-permeable blocks, inducing spurious velocity oscillations. The two-relaxation-times (TRT) LBM may control this effect thanks to free-tunable two-rates combination Λ . Moreover, the Brinkman-force-based BF-TRT schemes may maintain the nondimensional Darcy group and produce viscosity-independent permeability provided that the spatial distribution of Λ is fixed independently of the kinematic viscosity. Such a property is lost not only in the BF-BGK scheme but also by "partial bounce-back" TRT gray models, as shown in this work. Further, we propose a consistent and improved IBF-TRT model which vanishes viscosity correction via simple specific adjusting of the viscous-mode relaxation rate to local permeability value. This prevents the model from velocity fluctuations and, in parallel, improves for effective permeability measurements, from porous channel to multidimensions. The framework of our exact analysis employs a symbolic approach developed for both LBM and FEM in single and stratified, unconfined, and bounded channels. It shows that even with similar bulk discretization, BF, IBF, and FEM may manifest quite different velocity profiles on the coarse grids due to their intrinsic contrasts in the setting of interface continuity and no-slip conditions. While FEM enforces them on the grid vertexes, the LBM prescribes them implicitly. We derive effective LBM continuity conditions and show that the heterogeneous viscosity correction impacts them, a property also shared

  12. Room temperature synthesis of porous SiO2 thin films by plasma enhanced chemical vapor deposition

    Science.gov (United States)

    Barranco, A.; Cotrino, J.; Yubero, F.; Espinós, J. P.; González-Elipe, A. R.

    2004-07-01

    Silicon dioxide thin films with variable and controlled porosity have been prepared at room temperature by plasma enhanced chemical vapor deposition in an electron cyclotron resonance microwave reactor with a downstream configuration. The procedure consists of the deposition of successive cycles consisting of a sacrificial organic-polymeric layer and, afterward, a silicon dioxide layer. Toluene and oxygen are used as precursors of the organic layers and Si(CH3)3Cl and oxygen for the SiO2. During deposition of the latter, the organic layer is simultaneously burned off. In these conditions, the release of gases produced by oxidation of the organic-polymeric layer take place while the oxide layer is being deposited. Thus, modification of the nucleation and growing mechanism of the silicon oxide thin film take place. The porosity of the final porous SiO2 thin films increases with the thickness of the sacrificial organic layer. The porous SiO2 films prepared with the aforementioned method are free of carbon and chlorine contamination as confirmed by Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy. Depending on their porosity, the SiO2 thin films are either transparent or scattered visible light. The former have refractive index lower than that of thermal silicon dioxide and the latter show membranelike behavior in gas diffusion experiments. All the samples have good adhesion to the substrates used for the deposition, either polished Si wafer, glass plates, or standard porous supports. They have columnar microstructure, as determined by scanning electron microscopy. A preliminary ultraviolet-visible characterization of the optically transparent thin films reveals that transmission of light through glass increases by 7%-8% when the porous silica is deposited on this substrate. These films prove to be very efficient as antireflective coatings and are of interest for photovoltaic and similar applications

  13. Room temperature synthesis of porous SiO2 thin films by plasma enhanced chemical vapor deposition

    International Nuclear Information System (INIS)

    Silicon dioxide thin films with variable and controlled porosity have been prepared at room temperature by plasma enhanced chemical vapor deposition in an electron cyclotron resonance microwave reactor with a downstream configuration. The procedure consists of the deposition of successive cycles consisting of a sacrificial organic-polymeric layer and, afterward, a silicon dioxide layer. Toluene and oxygen are used as precursors of the organic layers and Si(CH3)3Cl and oxygen for the SiO2. During deposition of the latter, the organic layer is simultaneously burned off. In these conditions, the release of gases produced by oxidation of the organic-polymeric layer take place while the oxide layer is being deposited. Thus, modification of the nucleation and growing mechanism of the silicon oxide thin film take place. The porosity of the final porous SiO2 thin films increases with the thickness of the sacrificial organic layer. The porous SiO2 films prepared with the aforementioned method are free of carbon and chlorine contamination as confirmed by Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy. Depending on their porosity, the SiO2 thin films are either transparent or scattered visible light. The former have refractive index lower than that of thermal silicon dioxide and the latter show membranelike behavior in gas diffusion experiments. All the samples have good adhesion to the substrates used for the deposition, either polished Si wafer, glass plates, or standard porous supports. They have columnar microstructure, as determined by scanning electron microscopy. A preliminary ultraviolet-visible characterization of the optically transparent thin films reveals that transmission of light through glass increases by 7%-8% when the porous silica is deposited on this substrate. These films prove to be very efficient as antireflective coatings and are of interest for photovoltaic and similar applications

  14. Chemical reaction and radiation absorption effects on MHD micropolar fluid past a vertical porous plate in a rotating system

    International Nuclear Information System (INIS)

    This paper considers the effect of radiation absorption and chemical reaction on MHD free convection heat and mass transfer flow of a micropolar fluid in a rotating system. A uniform magnetic field acts perpendicular to the porous surface in which absorbs micropolar fluid with a constant suction velocity. The entire system rotates about the axes normal to the plate with uniform angular velocity Ω. The governing dimensionless equations for this investigation are solved analytically by using regular perturbation method. The effects of the various flow parameters and physical properties on the velocity, microrotation, temperature and concentration profiles across the boundary layer are investigated through graphs. Also the numerical results of velocity profiles of micropolar fluids are compared with the corresponding flow problems for a Newtonian fluid. (author)

  15. Fabrication of heterogeneous nanomaterial array by programmable heating and chemical supply within microfluidic platform towards multiplexed gas sensing application

    Science.gov (United States)

    Yang, Daejong; Kang, Kyungnam; Kim, Donghwan; Li, Zhiyong; Park, Inkyu

    2015-01-01

    A facile top-down/bottom-up hybrid nanofabrication process based on programmable temperature control and parallel chemical supply within microfluidic platform has been developed for the all liquid-phase synthesis of heterogeneous nanomaterial arrays. The synthesized materials and locations can be controlled by local heating with integrated microheaters and guided liquid chemical flow within microfluidic platform. As proofs-of-concept, we have demonstrated the synthesis of two types of nanomaterial arrays: (i) parallel array of TiO2 nanotubes, CuO nanospikes and ZnO nanowires, and (ii) parallel array of ZnO nanowire/CuO nanospike hybrid nanostructures, CuO nanospikes and ZnO nanowires. The laminar flow with negligible ionic diffusion between different precursor solutions as well as localized heating was verified by numerical calculation and experimental result of nanomaterial array synthesis. The devices made of heterogeneous nanomaterial array were utilized as a multiplexed sensor for toxic gases such as NO2 and CO. This method would be very useful for the facile fabrication of functional nanodevices based on highly integrated arrays of heterogeneous nanomaterials.

  16. Fabrication of heterogeneous nanomaterial array by programmable heating and chemical supply within microfluidic platform towards multiplexed gas sensing application.

    Science.gov (United States)

    Yang, Daejong; Kang, Kyungnam; Kim, Donghwan; Li, Zhiyong; Park, Inkyu

    2015-01-01

    A facile top-down/bottom-up hybrid nanofabrication process based on programmable temperature control and parallel chemical supply within microfluidic platform has been developed for the all liquid-phase synthesis of heterogeneous nanomaterial arrays. The synthesized materials and locations can be controlled by local heating with integrated microheaters and guided liquid chemical flow within microfluidic platform. As proofs-of-concept, we have demonstrated the synthesis of two types of nanomaterial arrays: (i) parallel array of TiO2 nanotubes, CuO nanospikes and ZnO nanowires, and (ii) parallel array of ZnO nanowire/CuO nanospike hybrid nanostructures, CuO nanospikes and ZnO nanowires. The laminar flow with negligible ionic diffusion between different precursor solutions as well as localized heating was verified by numerical calculation and experimental result of nanomaterial array synthesis. The devices made of heterogeneous nanomaterial array were utilized as a multiplexed sensor for toxic gases such as NO2 and CO. This method would be very useful for the facile fabrication of functional nanodevices based on highly integrated arrays of heterogeneous nanomaterials. PMID:25634814

  17. Heterogeneous Catalysis

    OpenAIRE

    Schlögl, R.

    2015-01-01

    A heterogeneous catalyst is a functional material that continually creates active sites with its reactants under reaction conditions. These sites change the rates of chemical reactions of the reactants localized on them without changing the thermodynamic equilibrium between the materials.

  18. Continent-ocean chemical heterogeneity in the mantle based on seismic tomography.

    Science.gov (United States)

    Forte, A M; Dziewonski, A M; O'connell, R J

    1995-04-21

    Seismic models of global-scale lateral heterogeneity in the mantle show systematic differences below continents and oceans that are too large to be purely thermal in origin. An inversion of the geoid, based on a seismic model that includes viscous flow in the mantle, indicates that the differences beneath continents and oceans can be accounted for by differences in composition in the upper mantle superposed on mantle-wide thermal heterogeneities. The net continent-ocean density differences, integrated over depth, are small and cause only a low flux of mass and heat across the asthenosphere and mantle transition zone. PMID:17746544

  19. Transfers in heterogeneous environments; Transferts en milieux heterogenes

    Energy Technology Data Exchange (ETDEWEB)

    Flesselles, J.M. [Saint-Gobain Recherche, 93 - Aubervilliers (France); Gouesbet, G.; Mees, L.; Roze, C.; Girasole, Th.; Grehan, G. [Laboratoire d' Electromagnetisme et Systemes Particulaires (LESP), UMR CNRS 6614, CORIA. Universite de Rouen et INSA de Rouen, 76 - Saint-Etienne du Rouvray (France); Goyheneche, J.M.; Vignoles, G.; Coindreau, O. [Laboratoire des Composites Thermostructuraux (LCTS), UMR 5801, 33 - Pessac (France); Moyne, Ch. [LEMTA (UMR 7563) CNRS-INPL-UHP, 54 - Vandoeuvre les Nancy (France); Coussy, O. [Institut Navier - ENPC, 77 - Marne-la-Vallee (France); Lassabatere, Th. [Electricite de France Les Renardieres, Dept. Materiaux Mecanique des Composants, 77 - Moret sur Loing (France); Tadrist, L. [IUSTI - UMR 6595, 13 - Marseille (France)

    2004-07-01

    This document gathers the articles and transparencies of the invited talks given at the 2004 French congress of thermal engineering about transfers in heterogeneous environment. Content: transfer phenomena in industrial glass furnaces; simple and multiple scattering diagnosis by femto-second pulsed laser: application to particulate diagnoses; thermal modeling of thermo-structural composites; hybrid mixtures theory, average volumic measurement, periodical or stochastic homogenization: advance in scale change processes; thermo-hydro-chemical-mechanical coupling in porous medium: application to young concrete structures and to clay barriers of disposal facilities; transfers and flows in fluidization: recent advances and future challenges. (J.S.)

  20. Tailored Porous Materials

    Energy Technology Data Exchange (ETDEWEB)

    BARTON,THOMAS J.; BULL,LUCY M.; KLEMPERER,WALTER G.; LOY,DOUGLAS A.; MCENANEY,BRIAN; MISONO,MAKOTO; MONSON,PETER A.; PEZ,GUIDO; SCHERER,GEORGE W.; VARTULI,JAMES C.; YAGHI,OMAR M.

    1999-11-09

    Tailoring of porous materials involves not only chemical synthetic techniques for tailoring microscopic properties such as pore size, pore shape, pore connectivity, and pore surface reactivity, but also materials processing techniques for tailoring the meso- and the macroscopic properties of bulk materials in the form of fibers, thin films and monoliths. These issues are addressed in the context of five specific classes of porous materials: oxide molecular sieves, porous coordination solids, porous carbons, sol-gel derived oxides, and porous heteropolyanion salts. Reviews of these specific areas are preceded by a presentation of background material and review of current theoretical approaches to adsorption phenomena. A concluding section outlines current research needs and opportunities.

  1. Lie Group Solution for Free Convective Flow of a Nanofluid Past a Chemically Reacting Horizontal Plate in a Porous Media

    Directory of Open Access Journals (Sweden)

    M. M. Rashidi

    2014-01-01

    Full Text Available The optimal homotopy analysis method (OHAM is employed to investigate the steady laminar incompressible free convective flow of a nanofluid past a chemically reacting upward facing horizontal plate in a porous medium taking into account heat generation/absorption and the thermal slip boundary condition. Using similarity transformations developed by Lie group analysis, the continuity, momentum, energy, and nanoparticle volume fraction equations are transformed into a set of coupled similarity equations. The OHAM solutions are obtained and verified by numerical results using a Runge-Kutta-Fehlberg fourth-fifth order method. The effect of the emerging flow controlling parameters on the dimensionless velocity, temperature, and nanoparticle volume fraction have been presented graphically and discussed. Good agreement is found between analytical and numerical results of the present paper with published results. This close agreement supports our analysis and the accuracy of the numerical computations. This paper also includes a representative set of numerical results for reduced Nusselt and Sherwood numbers in a table for various values of the parameters. It is concluded that the reduced Nusselt number increases with the Lewis number and reaction parameter whist it decreases with the order of the chemical reaction, thermal slip, and generation parameters.

  2. Hysteresis and drift of spiral waves near heterogeneities: From chemical experiments to cardiac simulations

    Science.gov (United States)

    Nakouzi, Elias; Totz, Jan Frederik; Zhang, Zhihui; Steinbock, Oliver; Engel, Harald

    2016-02-01

    Dissipative patterns in excitable reaction-diffusion systems can be strongly affected by spatial heterogeneities. Using the photosensitive Belousov-Zhabotinsky reaction, we show a hysteresis effect in the transition between free and pinned spiral rotation. The latter state involves the rotation around a disk-shaped obstacle with an impermeable and inert boundary. The transition is controlled by changes in light intensity. For permeable heterogeneities of higher excitability, we observe spiral drift along both linear and circular boundaries. Our results confirm recent theoretical predictions and, in the case of spiral drift, are further reproduced by numerical simulations with a modified Oregonator model. Additional simulations with a cardiac model show that orbital motion can also exist in anisotropic and three-dimensional systems.

  3. Heterogeneous TiO2 Photocatalysis : Fundamental Chemical Aspects and Effects of Solid Phase Alterations

    OpenAIRE

    Diesen, Veronica

    2013-01-01

    Heterogeneous photocatalysis on TiO2 is an emerging green technology for water disinfection. The rationale for this technology is based on in-situ generation of highly reactive transitory species for degradation of organic and inorganic pollutants as well as microorganisms. Recent research has concentrated on improving the efficiency of the photocatalytic process, however, some fundamental information on the mechanistic aspects and rate limiting properties still remain elusive.     The focus ...

  4. The role of pellet thermal stability in reactor design for heterogeneously catalysed chemical reactions

    OpenAIRE

    Wijngaarden, R.J.; Westerterp, K.R.

    1992-01-01

    For exothermic fluid-phase reactions, a reactor which is cooled at the wall can exhibit multiplicity or parametric sensitivity. Moreover, for heterogeneously catalysed exothermic fluid-phase reactions, each of the catalytically active pellets in the reactor can exhibit multiplicity. Both forms of multiplicity can lead to thermal instability and as such have to be taken into account in reactor design. Here the effect of both instabilities is quantified. To this end, simple first-order kinetics...

  5. Self-consistent nonlocal feedback theory for electrocatalytic swimmers with heterogeneous surface chemical kinetics

    Science.gov (United States)

    Nourhani, Amir; Crespi, Vincent H.; Lammert, Paul E.

    2015-06-01

    We present a self-consistent nonlocal feedback theory for the phoretic propulsion mechanisms of electrocatalytic micromotors or nanomotors. These swimmers, such as bimetallic platinum and gold rods catalyzing decomposition of hydrogen peroxide in aqueous solution, have received considerable theoretical attention. In contrast, the heterogeneous electrochemical processes with nonlocal feedback that are the actual "engines" of such motors are relatively neglected. We present a flexible approach to these processes using bias potential as a control parameter field and a locally-open-circuit reference state, carried through in detail for a spherical motor. While the phenomenological flavor makes meaningful contact with experiment easier, required inputs can also conceivably come from, e.g., Frumkin-Butler-Volmer kinetics. Previously obtained results are recovered in the weak-heterogeneity limit and improved small-basis approximations tailored to structural heterogeneity are presented. Under the assumption of weak inhomogeneity, a scaling form is deduced for motor speed as a function of fuel concentration and swimmer size. We argue that this form should be robust and demonstrate a good fit to experimental data.

  6. Successful definition of nanowire and porous Si regions of different porosity levels by regular positive photoresist using metal-assisted chemical etching

    International Nuclear Information System (INIS)

    A simple and efficient method for selective formation of porous Si areas using regular photoresist as a masking layer is presented. Such a simple masking layer is sufficient to create a wide range of porosity levels through metal-assisted chemical etching (MaCE) using platinum, palladium and silver nanoparticles. Reproducible porous areas with a minimum feature size of 5 µm were produced on Si wafers. The pore size and height are the functions of the etching time and type of nanoparticles. Using Ag nanopaticles we have been able to obtain Si nanowires of about 30 µm height. Based on these results, a combination of positive photoresist and MaCE seems to be a reliable way for micron and submicron patterning of nanowire and porous areas on Si wafers, which is simple, inexpensive and compatible with integrated circuit fabrication techniques

  7. Geochemical and fluid dynamic investigations into the nature of chemical heterogeneity in the earth's mantle. Doctoral thesis

    Energy Technology Data Exchange (ETDEWEB)

    Hauri, E.H.

    1992-09-01

    Variations in the abundances of elements and radiogenic isotopes in mantle derived periodotites and volcanic rocks are chemical integrals over time, space, and process, which ultimately contain information about the role of convection in the earth's mantle in creating, maintaining, and destroying geochemical heterogeneities. Successful inversion of these integrals extensive of these integrals requires extensive knowledge of the geochemical behavior of elements, the length scales of chemical variability, the evolution with time of geologic systems, the physical properties of mantle rocks, and the driving forces of phenomena which govern heat and mass transport in a dynamic earth. This dissertation attempts to add to this knowledge by examining the trace element and isotope geochemistry of mantle periodotites and oceanic island basalts, and by studying aspects of the flow of viscous fluids driven by thermal buoyancy.

  8. Hydrodynamic and Chemical Factors in Clogging by Montmorillonite in Porous Media

    OpenAIRE

    MAYS, DAVID C.; HUNT, JAMES R.

    2007-01-01

    Clogging by colloid deposits is important in water treatment filters, groundwater aquifers, and petroleum reservoirs. The complexity of colloid deposition and deposit morphology preclude models based on first principles, so this study extends an empirical approach to quantify clogging using a simple, one-parameter model. Experiments were conducted with destabilized suspensions of sodium- and calcium-montmorillonite to quantify the hydrodynamic and chemical factors important in clogging. Great...

  9. Enhancement of Bacterial Transport in Aerobic and Anaerobic Environments: Assessing the Effect of Metal Oxide Chemical Heterogeneities

    International Nuclear Information System (INIS)

    The goal of our research was to understand the fundamental processes that control microbial transport in physically and chemically heterogeneous aquifers and from this enhanced understanding determine the requirements for successful, field-scale delivery of microorganisms to metal contaminated subsurface sites. Our specific research goals were to determine; (1) the circumstances under which the preferential adsorption of bacteria to Fe, Mn, and Al oxyhydroxides influences field-scale bacterial transport, (2) the extent to which the adhesion properties of bacterial cells affect field-scale bacterial transport, (3) whether microbial Fe(III) reduction can enhance field-scale transport of Fe reducing bacteria (IRB) and other microorganisms and (4) the effect of field-scale physical and chemical heterogeneity on all three processes. Some of the spin-offs from this basic research that can improve biostimulation and bioaugmentation remediation efforts at contaminated DOE sites have included; (1) new bacterial tracking tools for viable bacteria; (2) an integrated protocol which combines subsurface characterization, laboratory-scale experimentation, and scale-up techniques to accurately predict field-scale bacterial transport; and (3) innovative and inexpensive field equipment and methods that can be employed to enhance Fe(III) reduction and microbial transport and to target microbial deposition under both aerobic and anaerobic conditions

  10. Bacteriophage adsorption during transport through porous media: Chemical perturbations and reversibility

    Science.gov (United States)

    Bales, R.C.; Hinkle, S.R.; Kroeger, T.W.; Stocking, K.; Gerba, C.P.

    1991-01-01

    In a series of seven column experiments, attachment of the bacteriophage PRD-1 and MS-2 to silica beads at pH's 5.0-5.5 was at least partially reversible; however, release of attached phage was slow and breakthrough curves exhibited significant tailing. Rate coefficients for attachment and detachment were on the order of 10-4 and 10-6-10-4 s-1, respectively. Corresponding time scales were hours for attachment and days for detachment. The sticking efficiency (??) for phage attachment was near 0.01. The rate of phage release was enhanced by raising pH and introducing surface-active chemical species, illustrating the importance of chemical perturbations in promoting biocolloid transport. In a series of batch experiments, MS-2 adsorbed strongly to a hydrophobic surface, octadecyltrichlorosilane-bonded silica, at both pH's 5 and 7. Adsorption to the unbonded silica at pH 5 was linear, but was 2.5 (with Ca2+) to 0.25% (without Ca2+) of that to the bonded surface. Neither MS-2 nor PRD-1 adsorbed to unbonded silica at pH 7. Hydrophobic effects appear to be important for adsorption of even relatively hydrophilic biocolloids. ?? 1991 American Chemical Society.

  11. Chemical heterogeneity of Mt. Etna magmas in the last 15 ka. Inferences on their mantle sources

    Science.gov (United States)

    Corsaro, Rosa Anna; Métrich, Nicole

    2016-05-01

    Primitive basaltic magmas are crucial in the study of the geochemical heterogeneity documented in Etna magmas and their inferred mantle sources. We undertook a systematic sampling of the less evolved basalts (Mg# > 50) erupted over the last 15 ka, a time period which corresponds to the activity of the youngest volcanic edifice of Mt. Etna complex, i.e. Mongibello volcano. We focused on lava flows and pyroclastites emplaced during 'deep-dyke fed' (DDF) eruptions which were driven by the rapid ascent of deeply-rooted magma intrusions that bypassed the shallow plumbing system of the volcano. All the samples were analyzed by the same laboratory to avoid analytical bias, to build a comprehensive dataset on their major and trace element compositions and to propose a coherent framework for interpreting the geochemical fingerprints of present-day Etna basalts. Trace element modeling, together with literature data for Sr isotopes, gave insight into long-term magmatic processes related to different melting degrees of the heterogeneous mantle beneath Mt Etna. DDF magma batches provide good snapshots of their mantle source heterogeneities that point to the variable involvement of clinopyroxenitic lithology, Rb-87Sr-Cl-rich fluid component(s) possibly controlled by their source mineralogy, and slab-derived fluids selectively enriched in alkalis (Rb, K). The ongoing alkali (Rb, K) enrichment of the present-day magmas, well manifest since the 1970s, is decoupled from that of Sr and Cl. We propose that this process is linked to mantle source composition and is concomitant with changes in both volcanological and seismotectonic patterns of the volcano. There is no time evolution of DDF magma chemistry.

  12. Encapsulated nano-heat-sinks for thermal management of heterogeneous chemical reactions.

    Science.gov (United States)

    Zhang, Minghui; Hong, Yan; Ding, Shujiang; Hu, Jianjun; Fan, Yunxiao; Voevodin, Andrey A; Su, Ming

    2010-12-01

    This paper describes a new way to control temperatures of heterogeneous exothermic reactions such as heterogeneous catalytic reaction and polymerization by using encapsulated nanoparticles of phase change materials as thermally functional additives. Silica-encapsulated indium nanoparticles and silica encapsulated paraffin nanoparticles are used to absorb heat released in catalytic reaction and to mitigate gel effect of polymerization, respectively. The local hot spots that are induced by non-homogenous catalyst packing, reactant concentration fluctuation, and abrupt change of polymerization rate lead to solid to liquid phase change of nanoparticle cores so as to avoid thermal runaway by converting energies from exothermic reactions to latent heat of fusion. By quenching local hot spots at initial stage, reaction rates do not rise significantly because the thermal energy produced in reaction is isothermally removed. Nanoparticles of phase change materials will open a new dimension for thermal management of exothermic reactions to quench local hot spots, prevent thermal runaway of reaction, and change product distribution. PMID:20967399

  13. Processing of Biomorphic Porous Ceramics by Chemical Vapor Infiltration and Reaction Technique (CVI-R)

    OpenAIRE

    Ghanem, Hanadi

    2008-01-01

    Biomorphic ceramics are a new class of materials derived from natural biopolymers that can be fabricated by different ceramization routes in order to produce carbides, nitrides and oxides, depending on the processing conditions. A wide variety of non-oxide ceramics such as SiC, Si3N4 and SiC-Si3N4 in addition to oxide-based ceramics like TiO2 have been produced in this study from carbonized paper preforms using Chemical Vapor Infiltration and Reaction (CVI-R) technique. For production of non-...

  14. Nanoscale multilayered and porous carbide interphases prepared by pressure-pulsed reactive chemical vapor deposition for ceramic matrix composites

    Energy Technology Data Exchange (ETDEWEB)

    Jacques, S., E-mail: jacques@lcts.u-bordeaux1.fr [LCTS, University of Bordeaux 1, CNRS, Herakles-Safran, CEA, 3 allee de la Boetie, F-33600 Pessac (France); Jouanny, I.; Ledain, O.; Maillé, L.; Weisbecker, P. [LCTS, University of Bordeaux 1, CNRS, Herakles-Safran, CEA, 3 allee de la Boetie, F-33600 Pessac (France)

    2013-06-15

    In Ceramic Matrix Composites (CMCs) reinforced by continuous fibers, a good toughness is achieved by adding a thin film called “interphase” between the fiber and the brittle matrix, which acts as a mechanical fuse by deflecting the matrix cracks. Pyrocarbon (PyC), with or without carbide sub-layers, is typically the material of choice to fulfill this role. The aim of this work was to study PyC-free nanoscale multilayered carbide coatings as interphases for CMCs. Nanoscale multilayered (SiC–TiC){sub n} interphases were deposited by pressure-Pulsed Chemical Vapor Deposition (P-CVD) on single filament Hi-Nicalon fibers and embedded in a SiC matrix sheath. The thicknesses of the carbide interphase sub-layers could be made as low as a few nanometers as evidenced by scanning and transmission electron microscopy. By using the P-ReactiveCVD method (P-RCVD), in which the TiC growth involves consumption of SiC, it was not only possible to obtain multilayered (SiC–TiC){sub n} films but also TiC films with a porous multilayered microstructure as a result of the Kirkendall effect. The porosity in the TiC sequences was found to be enhanced when some PyC was added to SiC prior to total RCVD consumption. Because the porosity volume fraction was still not high enough, the role of mechanical fuse of the interphases could not be evidenced from the tensile curves, which remained fully linear even when chemical attack of the fiber surface was avoided.

  15. Nanoscale multilayered and porous carbide interphases prepared by pressure-pulsed reactive chemical vapor deposition for ceramic matrix composites

    International Nuclear Information System (INIS)

    In Ceramic Matrix Composites (CMCs) reinforced by continuous fibers, a good toughness is achieved by adding a thin film called “interphase” between the fiber and the brittle matrix, which acts as a mechanical fuse by deflecting the matrix cracks. Pyrocarbon (PyC), with or without carbide sub-layers, is typically the material of choice to fulfill this role. The aim of this work was to study PyC-free nanoscale multilayered carbide coatings as interphases for CMCs. Nanoscale multilayered (SiC–TiC)n interphases were deposited by pressure-Pulsed Chemical Vapor Deposition (P-CVD) on single filament Hi-Nicalon fibers and embedded in a SiC matrix sheath. The thicknesses of the carbide interphase sub-layers could be made as low as a few nanometers as evidenced by scanning and transmission electron microscopy. By using the P-ReactiveCVD method (P-RCVD), in which the TiC growth involves consumption of SiC, it was not only possible to obtain multilayered (SiC–TiC)n films but also TiC films with a porous multilayered microstructure as a result of the Kirkendall effect. The porosity in the TiC sequences was found to be enhanced when some PyC was added to SiC prior to total RCVD consumption. Because the porosity volume fraction was still not high enough, the role of mechanical fuse of the interphases could not be evidenced from the tensile curves, which remained fully linear even when chemical attack of the fiber surface was avoided.

  16. Nanoscale multilayered and porous carbide interphases prepared by pressure-pulsed reactive chemical vapor deposition for ceramic matrix composites

    Science.gov (United States)

    Jacques, S.; Jouanny, I.; Ledain, O.; Maillé, L.; Weisbecker, P.

    2013-06-01

    In Ceramic Matrix Composites (CMCs) reinforced by continuous fibers, a good toughness is achieved by adding a thin film called "interphase" between the fiber and the brittle matrix, which acts as a mechanical fuse by deflecting the matrix cracks. Pyrocarbon (PyC), with or without carbide sub-layers, is typically the material of choice to fulfill this role. The aim of this work was to study PyC-free nanoscale multilayered carbide coatings as interphases for CMCs. Nanoscale multilayered (SiC-TiC)n interphases were deposited by pressure-Pulsed Chemical Vapor Deposition (P-CVD) on single filament Hi-Nicalon fibers and embedded in a SiC matrix sheath. The thicknesses of the carbide interphase sub-layers could be made as low as a few nanometers as evidenced by scanning and transmission electron microscopy. By using the P-ReactiveCVD method (P-RCVD), in which the TiC growth involves consumption of SiC, it was not only possible to obtain multilayered (SiC-TiC)n films but also TiC films with a porous multilayered microstructure as a result of the Kirkendall effect. The porosity in the TiC sequences was found to be enhanced when some PyC was added to SiC prior to total RCVD consumption. Because the porosity volume fraction was still not high enough, the role of mechanical fuse of the interphases could not be evidenced from the tensile curves, which remained fully linear even when chemical attack of the fiber surface was avoided.

  17. Combined Effects of Chemical Reaction and Wall Slip on MHD Flow in a Vertical Wavy Porous Space with Traveling Thermal Waves

    Directory of Open Access Journals (Sweden)

    Ramamoorthy MUTHURAJ

    2013-07-01

    Full Text Available This paper investigates the magnetohydrodynamic (MHD mixed convective heat and mass transfer flow in a vertical wavy porous space in the presence of a heat source with the combined effects of chemical reaction and wall slip condition. The dimensionless governing equations are perturbed into: mean (zeroth-order part and a perturbed part, using amplitude as a small parameter. The perturbed quantities are obtained by perturbation series expansion for small wavelength in which terms of exponential order arise. The results obtained show that the velocity, temperature and concentration fields are appreciably influenced by the presence of chemical reaction, magnetic field, porous medium, heat source/sink parameter and wall slip condition. Further, the results of the skin friction and rate of heat and mass transfer at the wall are presented for various values of parameters entering into the problem and discussed with the help of graphs.

  18. Perturbation analysis of magnetohydrodynamics oscillatory flow on convective-radiative heat and mass transfer of micropolar fluid in a porous medium with chemical reaction

    Directory of Open Access Journals (Sweden)

    Dulal Pal

    2016-03-01

    Full Text Available This paper deals with the perturbation analysis of mixed convection heat and mass transfer of an oscillatory viscous electrically conducting micropolar fluid over an infinite moving permeable plate embedded in a saturated porous medium in the presence of transverse magnetic field. Analytical solutions are obtained for the governing basic equations. The effects of permeability, chemical reaction, viscous dissipation, magnetic field parameter and thermal radiation on the velocity distribution, micro-rotation, skin friction and wall couple stress coefficients are analyzed in detail. The results indicate that the effect of increasing the chemical reaction has a tendency to decrease the skin friction coefficient at the wall, while opposite trend is seen by increasing the permeability parameter of the porous medium. Also micro-rotational velocity distribution increases with an increase in the magnetic field parameter.

  19. Kinetics of microbial degradation of deicing chemicals in percolated porous media - the modeling perspective

    Science.gov (United States)

    Wehrer, Markus; Lissner, Heidi; Totsche, Kai

    2013-04-01

    A quantitative knowledge of the fate of deicing chemicals in the subsurface can be provided by analysis of laboratory and field experiments with numerical simulation models. In the present study, experimental data of microbial degradation of the deicing chemical propylene glycol (PG) under flow conditions in soil columns and field lysimeters were simulated to analyze the process conditions of degradation and to obtain the according parameters. Results from the column experiment were evaluated applying different scenarios of an advection-dispersion model using HYDRUS-1D. To reconstruct the data, different competing degradation models were included, i.e., zero order, first order and inclusion of a growing and decaying biomass. The general breakthrough behavior of propylene glycol in soil columns can be simulated well using a coupled model of solute transport and degradation with growth and decay of biomass. The susceptibility of the model to non-unique solutions was investigated using systematical forward and inverse simulations. We found that the model tends to equifinal solutions under certain conditions. Complex experimental boundary conditions can help to avoid this. Under field conditions, the situation is far more complex than in the laboratory. Studying the fate of PG with undisturbed lysimeters we found that aerobic and anaerobic degradation occurs simultaneously. We attribute this to the physical structure and the aggregated nature of the undisturbed soil material . This results in the presence of spatially disjoint oxidative and reductive regions of microbial activity and requires, but is not fully reflected by a dual porosity model. Currently, the numerical simulation of this system is in progress, considering several flow and transport models. A stochastic global search algorithm (DREAM-ZS) is used in conjuction with HYDRUS-1D to avoid local minima in the inverse simulations. The study shows the current limitations and potentials of modeling degradation

  20. Treatment of Actual Chemical Wastewater by a Heterogeneous Fenton Process Using Natural Pyrite

    OpenAIRE

    Liang Sun; Yan Li; Aimin Li

    2015-01-01

    Wastewater from chemical plants has remarkable antibiotic effects on the microorganisms in traditional biological treatment processes. An enhanced Fenton system catalyzed by natural pyrite was developed to degrade this kind of wastewater. Approximately 30% chemical oxygen demand (COD) was removed within 120 min when 50 mmol/L H2O2 and 10 g/L natural pyrite were used at initial pH from 1.8 to 7. A BOD5/COD enhancement efficiency of 210% and an acute biotoxicity removal efficiency of 84% were a...

  1. Effects of chemical reaction in thermal and mass diffusion of micropolar fluid saturated in porous regime with radiation and ohmic heating

    OpenAIRE

    Kumar Hitesh

    2016-01-01

    The present paper analyzes the chemically reacting free convection MHD micropolar flow, heat and mass transfer in porous medium past an infinite vertical plate with radiation and viscous dissipation. The non-linear coupled partial differential equations are solved numerically using an implicit finite difference scheme known as Keller-box method. The results for concentration, transverse velocity, angular velocity and temperature are obtained and effects of ...

  2. Heterogeneity in physical, chemical and plankton-community structures in Lake Tanganyika

    NARCIS (Netherlands)

    Langenberg, V.T.; Tumba, J.M.; Tshibangu, K.; Lukwesa, C.; Chitamwebwa, D.; Bwebwa, D.; Makasa, L.; Roijackers, R.M.M.

    2008-01-01

    From 28 August to 6 September 1995, we monitored the lake-wide physical, chemical and biological properties of the pelagic waters in Lake Tanganyika. The aim of this study was to examine the spatial environmental variability and its relation to fluctuations in plankton abundance and community assemb

  3. Advanced Biocatalytic Processing of Heterogeneous Lignocellulosic Feedstocks to a Platform Chemical Intermediate (Lactic acid Ester)

    Energy Technology Data Exchange (ETDEWEB)

    Dr. Sharon Shoemaker

    2004-09-03

    The development of commercial boi-based processes and products derived from agricultural waste biomass has the potential for significant impact on the economy and security of our nation. Adding value, rather than disposing of the waste of agriculture, can solve an environmental problem and reduce our dependence on foreign sources of fossil fuel for production of chemicals, materials and fuels.

  4. Porous carbons

    Indian Academy of Sciences (India)

    Satish M Manocha

    2003-02-01

    Carbon in dense as well as porous solid form is used in a variety of applications. Activated porous carbons are made through pyrolysis and activation of carbonaceous natural as well as synthetic precursors. Pyrolysed woods replicate the structure of original wood but as such possess very low surface areas and poor adsorption capacities. On activation, these exhibit increased adsorption volumes of 0.5–0.8 cm3 /gm and surface areas of 700–1800 m2 /gm depending on activation conditions, whether physical or chemical. Former carbons possess mixed pore size distribution while chemically activated carbons predominantly possess micropores. Thus, these carbons can be used for adsorption of wide distributions of molecules from gas to liquid. The molecular adsorption within the pores is due to single layer or multilayer molecule deposition at the pore walls and hence results in different types of adsorption isotherm. On the other hand, activated carbon fibres with controlled microporous structure and surface area in the range of 2500 m2 /gm can be developed by controlled pyrolysis and physical activation of amorphous carbon fibres. Active carbon fibres with unmatchable pore structure and surface characteristics are present and futuristic porous materials for a number of applications from pollution control to energy storage.

  5. Asian dust storm observed at a rural mountain site in southern China: chemical evolution and heterogeneous photochemistry

    Directory of Open Access Journals (Sweden)

    W. Nie

    2012-12-01

    Full Text Available Heterogeneous processes on dust particles are important for understanding the chemistry and radiative balance of the atmosphere. This paper investigates an intense Asian dust storm episode observed at Mount Heng (1269 m a.s.l. in southern China on 24–26 April 2009. A set of aerosol and trace gas data collected during the study was analyzed to investigate their chemical evolution and heterogeneous photochemistry as the dust traveled to southern China. Results show that the mineral dust arriving at Mt. Heng experienced significant modifications during transport, with large enrichments in secondary species (sulfate, nitrate, and ammonium compared with the dust composition collected at an upwind mountain top site (Mount Hua. A photochemical age "clock" (−Log10(NOx/NOy was employed to quantify the atmospheric processing time. The result indicates an obvious increase in the abundance of secondary water-soluble ions in dust particles with the air mass atmospheric processing time. Based on the observations, a 4-stage evolution process is proposed for carbonate-containing Asian dust, starting from fresh dust to particles coated with hydrophilic and acidic materials. Daytime-enhanced nitrite formation on the dust particles was also observed, which indicates the recent laboratory result of the TiO2 photocatalysis of NO2 as a potential source of nitrite and nitrous acid.

  6. Asian dust storm observed at a rural mountain site in Southern China: chemical evolution and heterogeneous photochemistry

    Directory of Open Access Journals (Sweden)

    W. Nie

    2012-08-01

    Full Text Available Heterogeneous processes on dust particles are important for understanding the chemistry and radiative balance of the atmosphere. This paper investigates an intense Asian dust storm episode observed at Mount Heng (1250 m a.s.l. in Southern China on 24–26 April 2009. A set of aerosol and trace gas data collected during the study was analyzed to investigate their chemical evolution and heterogeneous photochemistry as the dust traveled to Southern China. Results show that the mineral dust arriving at Mt. Heng experienced significant modifications during transport, with large enrichments in secondary species (sulfate, nitrate, and ammonium compared with the dust composition collected at an upwind mountain top site (Mount Hua. A photochemical age "clock" (−log10(NOx/NOy was employed to quantify the atmospheric processing time. The result indicates an obvious increase in the abundance of secondary water-soluble ions in dust particles with the air mass' photochemical age. Based on the observations, a 4-stage evolution process is proposed for carbonate-rich Asian dust, starting from fresh dust to particles coated with hydrophilic and acidic materials. Daytime-enhanced nitrite formation on the dust particles was also observed, which indicates the recent laboratory result of the TiO2 photocatalysis of NO2 as a potential source of nitrite and nitrous acid.

  7. Spatial Heterogeneity and Imperfect Mixing in Chemical Reactions: Visualization of Density-Driven Pattern Formation

    OpenAIRE

    2009-01-01

    Imperfect mixing is a concern in industrial processes, everyday processes (mixing paint, bread machines), and in understanding salt water-fresh water mixing in ecosystems. The effects of imperfect mixing become evident in the unstirred ferroin-catalyzed Belousov-Zhabotinsky reaction, the prototype for chemical pattern formation. Over time, waves of oxidation (high ferriin concentration, blue) propagate into a background of low ferriin concentration (red); their structure reflects in part the ...

  8. Transformation of Sorbitol to Biofuels by Heterogeneous Catalysis: Chemical and Industrial Considerations

    International Nuclear Information System (INIS)

    Decreasing oil supplies and increasing energy demand provide incentives to find alternative fuels. First, the valorisation of edible crops for ethanol and bio-diesel production led to first generation biofuels. Nowadays, research is focused on lignocellulosic biomass as a source of renewable carbon (second generation biofuels). Whereas the cellulosic ethanol production is in progress, a new way consisting of the transformation of ex-lignocellulose sugars and polyols towards light hydrocarbons by heterogeneous catalysis in aqueous phase has been recently described. This process is performed under mild conditions (T < 300 deg. C and P < 50 bar). It requires on one hand hydrogen formation by catalytic reforming of carbohydrates in aqueous phase and on the other hand, the dehydration/hydrogenation of polyols leading to alkanes by selective C-O bond cleavages. The challenge here is to conceive multifunctional catalytic systems that are stable, active and selective under the reaction conditions. The aim of this article is to present the involved reactions, the catalytic systems described in literature for that kind of transformation and examples of industrial applications. (authors)

  9. Heterogeneity of Physico-Chemical Properties in Structured Soils and Its Consequences

    Institute of Scientific and Technical Information of China (English)

    E. JASINSKA; H. WETZEL; T. BAUMGARTL; R. HORN

    2006-01-01

    Structured soils are characterized by the presence of inter- and intra-aggregate pore systems and aggregates, which show varying chemical, physical, and biological properties depending on the aggregate type and land use system. How far these aspects also affect the ion exchange processes and to what extent the interaction between the carbon distribution and kind of organic substances affect the internal soil strength as well as hydraulic properties like wettability are still under discussion. Thus, the objective of this research was to clarify the effect of soil aggregation on physical and chemical properties of structured soils at two scales: homogenized material and single aggregates. Data obtained by sequentially peeling off soil aggregates layers revealed gradients in the chemical composition from the aggregate surface to the aggregatecore. In aggregates from long term untreated forest soils we found lower amounts of carbon in the external layer, while in arable soils the differentiation was not pronounced. However, soil aggregates originating from these sites exhibited a higher concentration of microbial activity in the outer aggregate layer and declined towards the interior. Furthermore,soil depth and the vegetation type affected the wettability. Aggregate strength depended on water suction and differences in tillage treatments.

  10. The physico-chemical, antigenic, and functional heterogeneity of human serum amyloid A

    International Nuclear Information System (INIS)

    In the present study we attempted to develop a rapid method to isolate serum amyloid A isomers (SAA is.) and to determine whether this physicochemical heterogeneity corresponds to an antigenic and functional one. Pure human low molecular SAA (SAAL) was prepared from the serum of 6 patients (pts.) using standard techniques. Preparative isoelectric focusing in agarose/sephadex gels was used to separate SAAL is. Monoclonal antibodies (m. abs.) to SAAL and to AA were prepared by hybridization of P3XU-1 nonsecretory murine myeloma cells with murine spleen cells from Balb/c mice immunized with pooled SAAL and AA respectively. Four distinctly migrating SAAL isomers with PI's of 4.9, 5.8, 6.6, and 7.2 were isolated from 6 pts. while only three isomers were separated from the pt. with myasthenia gravis. Four m. abs. to SAAL, one to AA, six m. abs. to SAAL-2 is. and one to SAAL-1 is. were generated in murine ascitic fluid. Dishes coated with the four human SAA is., human AA, various mammalian and human proteins as well as with serum from 31 pts. with metastatic Ca. and 23 pts. with inflammatory diseases (ID) were reacted with the m. abs. The amount of binding was determined using 125I labelled goat antimouse serum. The m. abs. to SAA were found specific for human SAA recognizing two different patterns in relationship to the intensity of binding to SAA is. One of them (7A2-43) had a greater affinity for SAA from pts with ID, while the other (5A6-5) reacted stronger with SAA from pts with metastatic Ca

  11. Heterogeneous physical and chemical processes in a rarefied-gas flow in channels

    Science.gov (United States)

    Rebrov, A. K.; Yudin, I. B.

    2016-05-01

    A flow with physical and chemical reactions on hot surfaces is investigated. On the basis of physical experiments, determining the hydrogen-dissociation degree in rarefied gas and calculation of the flow by the method of direct simulation Monte Carlo (DSMC), it is possible to specify certain unknown constants of interaction of molecules and atoms with a tungsten surface. By the example of the hydrogen flow in a hightemperature tungsten cylindrical channel, the role of dissociation, sorption, and recombination processes is shown in a wide range of flow regimes from free-molecular to continuum.

  12. NANOSTRUCTURED POROUS SILICON AND LUMINESCENT POLYSILOLES AS CHEMICAL SENSORS FOR CARCINOGENIC CHROMIUM(VI) AND ARSENIC(V)

    Science.gov (United States)

    The chief goal is to develop new selective solid state sensors for carcinogenic and toxic chromium(VI) and arsenic(V) in water based on redox quenching of the luminescence from nanostructured porous silicon and polysiloles.

  13. Long-lived proterozoic chemical heterogeneity of the sub-continental lithospheric mantle beneath northeastern Brazil

    International Nuclear Information System (INIS)

    Mechanisms suggested for lithospheric enrichment include the influx of metasomatizing agents derived from subducting slabs (Jahn et al., 1999, Peccerillo, 1999) or infiltration by asthenospheric melts during periods of regional extension (e.g., Beraton, 1999). These processes redistribute incompatible trace elements and lead to anomalous enrichment, a diagnostic feature of mantle metasomatism (Roden and Murthy, 1985). Enrichment in light rare earth elements and accompanying fractionation between Sm and Nd occur as a consequence of such processes, causing the decrease in the Sm/Nd ratio of the modified mantle reservoir. This behavior makes Sm-Nd model ages useful tool for constraining the timing of chemical changes in the mantle. This paper reports Sr-Nd isotope features of magmas generated from the sub-continental lithospheric mantle (SCLM) beneath the Borborema Province, northeastern Brazil. For this study, we focus on regional mantle-derived magmatism ranging in age from late-Neoproterozoic to Mesozoic and Cenozoic in the Rio Grande do Norte Domain (RGND), in the northernmost portion of the Borborema Province where the resulting mafic rocks are well exposed. The isotope data allow us to establish correlation between the timing of chemical modification processes in the mantle and the chronology of tectonic events previously defined for the Borborema Province (au)

  14. Treatment of Actual Chemical Wastewater by a Heterogeneous Fenton Process Using Natural Pyrite.

    Science.gov (United States)

    Sun, Liang; Li, Yan; Li, Aimin

    2015-11-01

    Wastewater from chemical plants has remarkable antibiotic effects on the microorganisms in traditional biological treatment processes. An enhanced Fenton system catalyzed by natural pyrite was developed to degrade this kind of wastewater. Approximately 30% chemical oxygen demand (COD) was removed within 120 min when 50 mmol/L H₂O₂ and 10 g/L natural pyrite were used at initial pH from 1.8 to 7. A BOD₅/COD enhancement efficiency of 210% and an acute biotoxicity removal efficiency of 84% were achieved. The COD removal efficiency was less sensitive to initial pH than was the classic Fenton process. Excessive amounts of pyrite and H₂O₂ did not negatively affect the pyrite Fenton system. The amount of aniline generated indicated that nitrobenzene reduction by pyrite was promoted using a low initial concentration of H₂O₂ (<5 mmol/L). Fluorescence excitation emission matrix analyses illustrated that H₂O₂ facilitated the reduction by natural pyrite of organic molecules containing an electron-withdrawing group to electron-donating group. Thus, the Fenton-like process catalyzed by pyrite can remediate wastewater containing organic pollutants under mild reaction conditions and provide an alternative environmentally friendly method by which to reuse natural pyrite. PMID:26516893

  15. Hierarchical porous NiCo2S4 hexagonal plates: Formation via chemical conversion and application in high performance supercapacitors

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Hierarchical porous NiCo2S4 hexagonal plates are prepared via hydrothermal method. • The architecture of hexagonal plates is composed by numbers of nanoparticles. • The evolution of phase and morphology are confirmed by XRD and SEM measurements. • NiCo2S4 hexagonal plates exhibit excellent cycling stability and rate performance. - Abstract: Design: and prepare electrode material with porous structure is an effective method to enhance the electrochemical performance in supercapacitors. In this work, we developed hierarchical porous NiCo2S4 hexagonal plates via hydrothermal method by controlling sulfidation process. Measurements, such as XRD and SEM, are used to investigate the morphological and structural evolution of the hierarchical porous NiCo2S4 hexagonal plates. With advantages of high electronic conductivity, the interconnected nanometer-sized subunits of the material and the existence of porous, which cause shorter distance for transportation of electrolyte ion, excellent electrochemical performances exhibit with a high specific capacitance of 852.5 F g−1 after 5000 cycles at a current density of 10 A g−1. The outstanding properties indicate hierarchical porous NiCo2S4 hexagonal plates are promising future electrode materials for supercapacitors

  16. Numerical investigation of variable viscosities and thermal stratification effects on MHD mixed convective heat and mass transfer past a porous wedge in the presence of a chemical reaction

    Institute of Scientific and Technical Information of China (English)

    I. Muhaimin; R. Kandasamy; Azme B. Khamis

    2009-01-01

    An analysis is presented to investigate the effects of variable viscosities and thermal stratification on the MHD mixed convective heat and mass transfer of a viscous, incompressible, and electrically conducting fluid past a porous wedge in the presence of a chemical reaction. The wall of the wedge is embedded in a uniform non-Darcian porous medium in order to allow for possible fluid wall suction or injection. The governing boundary layer equations are written into a dimensionless form by similarity transformations. The transformed coupled nonlinear ordinary differential equations are solved numerically with finite difference methods. Numerical calculations up to the third-order level of truncation are carried out for different values of dimensionless parameters. The results are presented graphically, and show that the flow field and other quantities of physical interest are significantly influenced by these parameters. The results are compared with those available in literature, and show excellent agreement.

  17. Morphological and optical properties changes in nanocrystalline Si (nc-Si) deposited on porous aluminum nanostructures by plasma enhanced chemical vapor deposition for Solar energy applications

    Energy Technology Data Exchange (ETDEWEB)

    Ghrib, M., E-mail: mondherghrib@yahoo.fr [Laboratoire de Photovoltaique (L.P.V.), Centre de Recherche et des Technologies de l' Energie, BP 95, Hammam-Lif 2050 (Tunisia); Gaidi, M.; Ghrib, T.; Khedher, N. [Laboratoire de Photovoltaique (L.P.V.), Centre de Recherche et des Technologies de l' Energie, BP 95, Hammam-Lif 2050 (Tunisia); Ben Salam, M. [L3M, Department of Physics, Faculty of Sciences of Bizerte, 7021 Zarzouna (Tunisia); Ezzaouia, H. [Laboratoire de Photovoltaique (L.P.V.), Centre de Recherche et des Technologies de l' Energie, BP 95, Hammam-Lif 2050 (Tunisia)

    2011-08-15

    Photoluminescence (PL) spectroscopy was used to determine the electrical band gap of nanocrystalline silicon (nc-Si) deposited by plasma enhancement chemical vapor deposition (PECVD) on porous alumina structure by fitting the experimental spectra using a model based on the quantum confinement of electrons in Si nanocrystallites having spherical and cylindrical forms. This model permits to correlate the PL spectra to the microstructure of the porous aluminum silicon layer (PASL) structure. The microstructure of aluminum surface layer and nc-Si films was systematically studied by atomic force microscopy (AFM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray diffraction (XRD). It was found that the structure of the nanocrystalline silicon layer (NSL) is dependent of the porosity (void) of the porous alumina layer (PAL) substrate. This structure was performed in two steps, namely the PAL substrate was prepared using sulfuric acid solution attack on an Al foil and then the silicon was deposited by plasma enhanced chemical vapor deposition (PECVD) on it. The optical constants (n and k as a function of wavelength) of the deposited films were obtained using variable angle spectroscopic ellipsometry (SE) in the UV-vis-NIR regions. The SE spectrum of the porous aluminum silicon layer (PASL) was modeled as a mixture of void, crystalline silicon and aluminum using the Cauchy model approximation. The specific surface area (SSA) was estimated and was found to decrease linearly when porosity increases. Based on this full characterization, it is demonstrated that the optical characteristics of the films are directly correlated to their micro-structural properties.

  18. Chemical Heterogeneity on Mercury's Surface Revealed by the MESSENGER X-ray Spectrometer

    Science.gov (United States)

    Weider, Shoshana Z.; Nittler, Larry R.; Starr, Richard D.; McCoy, Timothy J.; Stockstill-Cahill, Karen R.; Byrne, Paul K.; Denevi, Brett W.; Head, James W.; Solomon, Sean C.

    2012-01-01

    We present the analysis of 205 spatially resolved measurements of the surfacecomposition of Mercury from MESSENGERs X-Ray Spectrometer. The surfacefootprints of these measurements are categorized according to geological terrain. Northernsmooth plains deposits and the plains interior to the Caloris basin differ compositionallyfrom older terrain on Mercury. The older terrain generally has higher MgSi, SSi, andCaSi ratios, and a lower AlSi ratio than the smooth plains. Mercurys surface mineralogyis likely dominated by high-Mg mafic minerals (e.g., enstatite), plagioclase feldspar, andlesser amounts of Ca, Mg, andor Fe sulfides (e.g., oldhamite). The compositionaldifference between the volcanic smooth plains and the older terrain reflects differentabundances of these minerals and points to the crystallization of the smooth plains from amore chemically evolved magma source. High-degree partial melts of enstatite chondritematerial provide a generally good compositional and mineralogical match for much ofthe surface of Mercury. An exception is Fe, for which the low surface abundance onMercury is still higher than that of melts from enstatite chondrites and may indicate anexogenous contribution from meteoroid impacts.

  19. Advances and Recent Trends in Heterogeneous Photo(Electro-Catalysis for Solar Fuels and Chemicals

    Directory of Open Access Journals (Sweden)

    James Highfield

    2015-04-01

    Full Text Available In the context of a future renewable energy system based on hydrogen storage as energy-dense liquid alcohols co-synthesized from recycled CO2, this article reviews advances in photocatalysis and photoelectrocatalysis that exploit solar (photonic primary energy in relevant endergonic processes, viz., H2 generation by water splitting, bio-oxygenate photoreforming, and artificial photosynthesis (CO2 reduction. Attainment of the efficiency (>10% mandated for viable techno-economics (USD 2.00–4.00 per kg H2 and implementation on a global scale hinges on the development of photo(electrocatalysts and co-catalysts composed of earth-abundant elements offering visible-light-driven charge separation and surface redox chemistry in high quantum yield, while retaining the chemical and photo-stability typical of titanium dioxide, a ubiquitous oxide semiconductor and performance “benchmark”. The dye-sensitized TiO2 solar cell and multi-junction Si are key “voltage-biasing” components in hybrid photovoltaic/photoelectrochemical (PV/PEC devices that currently lead the field in performance. Prospects and limitations of visible-absorbing particulates, e.g., nanotextured crystalline α-Fe2O3, g-C3N4, and TiO2 sensitized by C/N-based dopants, multilayer composites, and plasmonic metals, are also considered. An interesting trend in water splitting is towards hydrogen peroxide as a solar fuel and value-added green reagent. Fundamental and technical hurdles impeding the advance towards pre-commercial solar fuels demonstration units are considered.

  20. Advances and recent trends in heterogeneous photo(electro)-catalysis for solar fuels and chemicals.

    Science.gov (United States)

    Highfield, James

    2015-01-01

    In the context of a future renewable energy system based on hydrogen storage as energy-dense liquid alcohols co-synthesized from recycled CO2, this article reviews advances in photocatalysis and photoelectrocatalysis that exploit solar (photonic) primary energy in relevant endergonic processes, viz., H2 generation by water splitting, bio-oxygenate photoreforming, and artificial photosynthesis (CO2 reduction). Attainment of the efficiency (>10%) mandated for viable techno-economics (USD 2.00-4.00 per kg H2) and implementation on a global scale hinges on the development of photo(electro)catalysts and co-catalysts composed of earth-abundant elements offering visible-light-driven charge separation and surface redox chemistry in high quantum yield, while retaining the chemical and photo-stability typical of titanium dioxide, a ubiquitous oxide semiconductor and performance "benchmark". The dye-sensitized TiO2 solar cell and multi-junction Si are key "voltage-biasing" components in hybrid photovoltaic/photoelectrochemical (PV/PEC) devices that currently lead the field in performance. Prospects and limitations of visible-absorbing particulates, e.g., nanotextured crystalline α-Fe2O3, g-C3N4, and TiO2 sensitized by C/N-based dopants, multilayer composites, and plasmonic metals, are also considered. An interesting trend in water splitting is towards hydrogen peroxide as a solar fuel and value-added green reagent. Fundamental and technical hurdles impeding the advance towards pre-commercial solar fuels demonstration units are considered. PMID:25884553

  1. Fabrication and Characterization of a Porous Silicon Drug Delivery System with an Initiated Chemical Vapor Deposition Temperature-Responsive Coating.

    Science.gov (United States)

    McInnes, Steven J P; Szili, Endre J; Al-Bataineh, Sameer A; Vasani, Roshan B; Xu, Jingjing; Alf, Mahriah E; Gleason, Karen K; Short, Robert D; Voelcker, Nicolas H

    2016-01-12

    This paper reports on the fabrication of a pSi-based drug delivery system, functionalized with an initiated chemical vapor deposition (iCVD) polymer film, for the sustainable and temperature-dependent delivery of drugs. The devices were prepared by loading biodegradable porous silicon (pSi) with a fluorescent anticancer drug camptothecin (CPT) and coating the surface with temperature-responsive poly(N-isopropylacrylamide-co-diethylene glycol divinyl ether) (pNIPAM-co-DEGDVE) or non-stimulus-responsive poly(aminostyrene) (pAS) via iCVD. CPT released from the uncoated oxidized pSi control with a burst release fashion (∼21 nmol/(cm(2) h)), and this was almost identical at temperatures both above (37 °C) and below (25 °C) the lower critical solution temperature (LCST) of the switchable polymer used, pNIPAM-co-DEGDVE (28.5 °C). In comparison, the burst release rate from the pSi-pNIPAM-co-DEGDVE sample was substantially slower at 6.12 and 9.19 nmol/(cm(2) h) at 25 and 37 °C, respectively. The final amount of CPT released over 16 h was 10% higher at 37 °C compared to 25 °C for pSi coated with pNIPAM-co-DEGDVE (46.29% vs 35.67%), indicating that this material can be used to deliver drugs on-demand at elevated temperatures. pSi coated with pAS also displayed sustainable drug delivery profiles, but these were independent of the release temperature. These data show that sustainable and temperature-responsive delivery systems can be produced by functionalization of pSi with iCVD polymer films. Benefits of the iCVD approach include the application of the iCVD coating after drug loading without causing degradation of the drug commonly caused by exposure to factors such as solvents or high temperatures. Importantly, the iCVD process is applicable to a wide array of surfaces as the process is independent of the surface chemistry and pore size of the nanoporous matrix being coated. PMID:26654169

  2. Unsteady Natural Convective Flow over an Impulsively Started Semi-Infinite Vertical Plate in the Presence of Porous Medium with Chemical Reaction

    Directory of Open Access Journals (Sweden)

    LOGANATHAN PARASURAM

    2016-01-01

    Full Text Available An investigation is carried out to analyze the effects of heat and mass transfer over an impulsively started vertical plate in the presence of porous medium with chemical reaction. The unsteady, non-linear, coupled partial differential equations are solved by implicit finite difference scheme of Crank Nicolson type. The influence of various parameters like Prandtl number, Schmidt number, first order chemical reaction on the velocity, temperature and concentration are analyzed. The local skin friction, local Nusselt number, local Sherwood number, average skin friction, average Nusselt number and average Sherwood numbers are investigated. It is observed that the velocity and concentration boundary layer decreases with increasing chemical reaction. An increase in the Schmidt number reduces the concentration boundary layer thickness.

  3. High-speed deposition of dense, dendritic and porous SiO2 films by Nd: YAG laser chemical vapor deposition

    International Nuclear Information System (INIS)

    Dense, dendritic and porous SiO2 films were prepared by laser chemical vapor deposition (LCVD) using a high-power continuous-wave mode Nd: YAG laser (206 W) and a TEOS (tetraethyl orthosilicate) precursor. The effects of laser power (PL) and total chamber pressure (Ptot) on the microstructure and deposition rate (Rdep) were investigated. Amorphous SiO2 films were obtained independent of PL and Ptot. Flame formation was observed between the nozzle and the substrate at PL > 160 W and Ptot > 15 kPa. At PL = 206 W, dense, dendritic and porous SiO2 films were obtained at Ptot tot = 23 kPa and Ptot > 25 kPa, respectively. The Rdep increased thousands of times under flame formation conditions, the highest Rdep being reached at 1200 μm h-1, 22,000 μm h-1 and 28,000 μm h-1 for the dense, dendritic and porous SiO2 films, respectively.

  4. A highly porous NiO/polyaniline composite film prepared by combining chemical bath deposition and electro-polymerization and its electrochromic performance

    Science.gov (United States)

    Xia, X. H.; Tu, J. P.; Zhang, J.; Wang, X. L.; Zhang, W. K.; Huang, H.

    2008-11-01

    A highly porous NiO/polyaniline (PANI) composite film was prepared on ITO glass by combining the chemical bath deposition and electro-polymerization methods, successively. The porous NiO film acts as a template for the preferential growth of PANI along NiO flakes, and the NiO/PANI composite film has an intercrossing net-like morphology. The electrochromic performance of the NiO/PANI composite film was investigated in 1 M LiClO4+1 mM HClO4/propylene carbonate (PC) by means of transmittance, cyclic voltammetry (CV) and chronoamperometry (CA) measurements. The NiO/PANI thin film exhibits a noticeable electrochromism with reversible color changes from transparent yellow to purple and presents quite good transmittance modulation with a variation of transmittance up to 56% at 550 nm. The porous NiO/polyaniline (PANI) composite film also shows good reaction kinetics with fast switching speed, and the response time for oxidation and reduction is 90 and 110 ms, respectively.

  5. A highly porous NiO/polyaniline composite film prepared by combining chemical bath deposition and electro-polymerization and its electrochromic performance

    International Nuclear Information System (INIS)

    A highly porous NiO/polyaniline (PANI) composite film was prepared on ITO glass by combining the chemical bath deposition and electro-polymerization methods, successively. The porous NiO film acts as a template for the preferential growth of PANI along NiO flakes, and the NiO/PANI composite film has an intercrossing net-like morphology. The electrochromic performance of the NiO/PANI composite film was investigated in 1 M LiClO4+1 mM HClO4/propylene carbonate (PC) by means of transmittance, cyclic voltammetry (CV) and chronoamperometry (CA) measurements. The NiO/PANI thin film exhibits a noticeable electrochromism with reversible color changes from transparent yellow to purple and presents quite good transmittance modulation with a variation of transmittance up to 56% at 550 nm. The porous NiO/polyaniline (PANI) composite film also shows good reaction kinetics with fast switching speed, and the response time for oxidation and reduction is 90 and 110 ms, respectively.

  6. Chemical reaction effect on an unsteady MHD free convection flow past a vertical porous plate in the presence of suction or injection

    Directory of Open Access Journals (Sweden)

    Shivaiah S.

    2012-01-01

    Full Text Available The objective of this paper is to analyze the effect of chemical reaction on unsteady magneto hydrodynamic free convective fluid flow past a vertical porous plate in the presence of suction or injection. The governing equations of the flow field are solved numerically by a finite element method. The effects of the various parameters on the velocity, temperature and concentration profiles are presented graphically and values of skin-friction coefficient, Nusselt number and Sherwood number for various values of physical parameters are presented through tables.

  7. Effects of chemical reaction in thermal and mass diffusion of micropolar fluid saturated in porous regime with radiation and ohmic heating

    Directory of Open Access Journals (Sweden)

    Kumar Hitesh

    2016-01-01

    Full Text Available The present paper analyzes the chemically reacting free convection MHD micropolar flow, heat and mass transfer in porous medium past an infinite vertical plate with radiation and viscous dissipation. The non-linear coupled partial differential equations are solved numerically using an implicit finite difference scheme known as Keller-box method. The results for concentration, transverse velocity, angular velocity and temperature are obtained and effects of various parameters on these functions are presented graphically. The numerical discussion with physical interpretations for the influence of various parameters also presented.

  8. On Combined Effects of Heat Transfer and Chemical Reaction for the Flow through an Asymmetric Channel with Orthogonally Deformable Porous Walls

    Directory of Open Access Journals (Sweden)

    Syed Tauseef Mohyud-Din

    2016-01-01

    Full Text Available The combined effects of heat transfer and chemical reaction are studied for the flow through a semi-infinite asymmetric channel with orthogonally deformable porous walls. The similarity transforms have been used to reduce the conservation laws to a corresponding system of nonlinear ordinary differential equations. The resulting equations are solved, both analytically and numerically, by using Homotopy Analysis Method (HAM and the fourth-order Runge-Kutta (RK-4 method, respectively. The convergence of the analytical solution is assured through the so-called total squared residual error analysis. The optimal values of auxiliary parameters are obtained by minimizing the total squared residual error.

  9. Effect of chemical heterogeneity of biodegradable polymers on surface energy: A static contact angle analysis of polyester model films.

    Science.gov (United States)

    Belibel, R; Avramoglou, T; Garcia, A; Barbaud, C; Mora, L

    2016-02-01

    Biodegradable and bioassimilable poly((R,S)-3,3 dimethylmalic acid) (PDMMLA) derivatives were synthesized and characterized in order to develop a new coating for coronary endoprosthesis enabling the reduction of restenosis. The PDMMLA was chemically modified to form different custom groups in its side chain. Three side groups were chosen: the hexyl group for its hydrophobic nature, the carboxylic acid and alcohol groups for their acid and neutral hydrophilic character, respectively. The sessile drop method was applied to characterize the wettability of biodegradable polymer film coatings. Surface energy and components were calculated. The van Oss approach helped reach not only the dispersive and polar acid-base components of surface energy but also acid and basic components. Surface topography was quantified by atomic force microscopy (AFM) and subnanometer average values of roughness (Ra) were obtained for all the analyzed surfaces. Thus, roughness was considered to have a negligible effect on wettability measurements. In contrast, heterogeneous surfaces had to be corrected by the Cassie-Baxter equation for copolymers (10/90, 20/80 and 30/70). The impact of this correction was quantified for all the wettability parameters. Very high relative corrections (%) were found, reaching 100% for energies and 30% for contact angles. PMID:26652458

  10. Porous silicon gettering

    Energy Technology Data Exchange (ETDEWEB)

    Tsuo, Y.S.; Menna, P.; Al-Jassim, M. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1995-08-01

    We have studied a novel extrinsic gettering method that utilizes the very large surface areas, produced by porous silicon etch on both front and back surfaces of the silicon wafer, as gettering sites. In this method, a simple and low-cost chemical etching is used to generate the porous silicon layers. Then, a high-flux solar furnace (HFSF) is used to provide high-temperature annealing and the required injection of silicon interstitials. The gettering sites, along with the gettered impurities, can be easily removed at the end the process. The porous silicon removal process consists of oxidizing the porous silicon near the end the gettering process followed by sample immersion in HF acid. Each porous silicon gettering process removes up to about 10 {mu}m of wafer thickness. This gettering process can be repeated so that the desired purity level is obtained.

  11. TOUGH2, Unsaturated Ground Water and Heat Transfer - T2VOC, H2O, Air, VOC Flow Simulation in Porous Multidimensional Media - iTOUGH2, Inverse Modeling for TOUGH2 Multiphase Flow Simulators - TOUGHREACT, Chemically reactive non-isothermal flows of multiphase fluids in porous and fractured media - TMVOCV1.0, Multicomponent, multiphase, nonisothermal flows of water, soil gas, volatile organic chemicals (VOCs) - ECO2N, a TOUGH2 fluid property module for mixtures of water-NaCl-CO2

    International Nuclear Information System (INIS)

    1 - Description of program or function: TOUGH2V2.0 is a new and improved version of TOUGH2 for simulating fluid flow and heat transfer in porous media. It is upwardly compatible with and includes all of the capabilities of the earlier version, including the flexibility to handle different fluid mixtures (water, water with tracer; water, CO2; water, air; water, air, with vapor pressure lowering; and water, hydrogen), facilities for processing of geometric data (computational grids), and an internal version control system to ensure referenceability of code applications. Improvements in TOUGH2V2.0 include (1) several new EOS modules for different fluid mixtures, including brines and water-soluble and volatile tracers, (2) enhanced capabilities for previously released fluid property modules, (3) description of diffusion and dispersion in multiphase systems, (4) strongly coupled flow and transport processes, (5) coupling between flow in geothermal reservoirs and well-bores in two-phase conditions, (6) tracer transport with sorption and radioactive decay, (7) flow in media with strong heterogeneity, and (8) a new package of preconditioned conjugate gradient routines for more robust solution of numerically difficult problems. In addition, numerous enhancements were made to facilitate applications to more diverse and demanding flow problems. The TZVOC code for three phase flow of water, air, and a non-aqueous phase liquid (NAPL) has been fully integrated into and is now part of the TOUGH2V2.0 program package. TOUGH2V2.0 comes with a new self-contained users guide that includes technical specifications, a complete reference of input data formats and a collection of sample problems. TOUGH2V2.0 is a multi-dimensional numerical model for simulating the coupled transport of water, vapor, air, and other fluids, and heat in porous and fractured media. iTOUGH2 (inverse TOUGH2) is a computer program that provides inverse modeling capabilities for the TOUGH2 code, a simulator for

  12. COF-Net on CNT-Net as a Molecularly Designed, Hierarchical Porous Chemical Trap for Polysulfides in Lithium-Sulfur Batteries.

    Science.gov (United States)

    Yoo, JongTae; Cho, Sung-Ju; Jung, Gwan Yeong; Kim, Su Hwan; Choi, Keun-Ho; Kim, Jeong-Hoon; Lee, Chang Kee; Kwak, Sang Kyu; Lee, Sang-Young

    2016-05-11

    The hierarchical porous structure has garnered considerable attention as a multiscale engineering strategy to bring unforeseen synergistic effects in a vast variety of functional materials. Here, we demonstrate a "microporous covalent organic framework (COF) net on mesoporous carbon nanotube (CNT) net" hybrid architecture as a new class of molecularly designed, hierarchical porous chemical trap for lithium polysulfides (Li2Sx) in Li-S batteries. As a proof of concept for the hybrid architecture, self-standing COF-net on CNT-net interlayers (called "NN interlayers") are fabricated through CNT-templated in situ COF synthesis and then inserted between sulfur cathodes and separators. Two COFs with different micropore sizes (COF-1 (0.7 nm) and COF-5 (2.7 nm)) are chosen as model systems. The effects of the pore size and (boron-mediated) chemical affinity of microporous COF nets on Li2Sx adsorption phenomena are theoretically investigated through density functional theory calculations. Benefiting from the chemical/structural uniqueness, the NN interlayers effectively capture Li2Sx without impairing their ion/electron conduction. Notably, the COF-1 NN interlayer, driven by the well-designed microporous structure, allows for the selective deposition/dissolution (i.e., facile solid-liquid conversion) of electrically inert Li2S. As a consequence, the COF-1 NN interlayer provides a significant improvement in the electrochemical performance of Li-S cells (capacity retention after 300 cycles (at charge/discharge rate = 2.0 C/2.0 C) = 84% versus 15% for a control cell with no interlayer) that lies far beyond those accessible with conventional Li-S technologies. PMID:27104986

  13. On the propagation of a quasi-static disturbance in a heterogeneous, deformable, and porous medium with pressure-dependent properties

    Energy Technology Data Exchange (ETDEWEB)

    Vasco, D.W.

    2011-10-01

    Using an asymptotic technique, valid when the medium properties are smoothly-varying, I derive a semi-analytic expression for the propagation velocity of a quasi-static disturbance traveling within a nonlinear-elastic porous medium. The phase, a function related to the propagation time, depends upon the properties of the medium, including the pressure-sensitivities of the medium parameters, and on pressure and displacement amplitude changes. Thus, the propagation velocity of a disturbance depends upon its amplitude, as might be expected for a nonlinear process. As a check, the expression for the phase function is evaluated for a poroelastic medium, when the material properties do not depend upon the fluid pressure. In that case, the travel time estimates agree with conventional analytic estimates, and with values calculated using a numerical simulator. For a medium with pressure-dependent permeability I find general agreement between the semi-analytic estimates and estimates from a numerical simulation. In this case the pressure amplitude changes are obtained from the numerical simulator.

  14. Transport in porous media

    Energy Technology Data Exchange (ETDEWEB)

    Dickenson, Eric [Univ. of California, Davis, CA (United States)

    1996-05-01

    A novel non-intrusive fluorescence imaging technique is used to study microscopic transport within porous media. The system consists of a column packed with heterogeneous-transparent particles and a refractive index-matched aqueous fluid seeded with fluorescent tracer particles or an organic dye. The flow through the column is illuminated by a planar sheet of laser beam and details of flow and transport through the porous regions can be observed microscopically and qualitative and quantitative transport information can be obtained. Various geometric, flow, and concentration quantities can be determined over a three dimensional volume within the column. The quantities include local and volumetrically averaged porosities, velocity and concentration fields, microscopic and volumetrically averaged dispersive fluxes and the dispersion coefficient. The qualitative and quantitative results will provide a better understanding for modeling of transport in porous media.

  15. Analysis of chemical dissolution of the barrier layer of porous oxide on aluminum thin films using a re-anodizing technique

    International Nuclear Information System (INIS)

    Chemical dissolution of the barrier layer of porous oxide formed on thin aluminum films (99.9% purity) in the 4% oxalic acid after immersion in 2 mol dm-3 sulphuric acid at 50 deg. C has been studied. The barrier layer thickness before and after dissolution was calculated using a re-anodizing technique. It has been shown that above 57 V the change in the growth mechanism of porous alumina films takes place. As a result, the change in the amount of regions in the barrier oxide with different dissolution rates is observed. The barrier oxide contains two layers at 50 V: the outer layer with the highest dissolution rate and the inner layer with a low dissolution rate. Above 60 V the barrier oxide contains three layers: the outer layer with a high dissolution rate, the middle layer with the highest dissolution rate and the inner layer with a low dissolution rate. We suggest that the formation of the outer layer of barrier oxide with a high dissolution rate is linked with the injection of protons or H3O+ ions from the electrolyte into the oxide film at the anodizing voltages above 57 V

  16. The influence of chemical post-etching and UV irradiation on the optical absorption and thermal diffusivity of porous silicon studied by photoacoustic technique

    International Nuclear Information System (INIS)

    We applied a photoacoustic (PA) technique to study the optical absorption and thermal diffusivity of porous silicon (PSi) samples. The PSi layers were formed on p-type Si wafers in an HF electrolyte. Three kinds of PSi samples that had undergone chemical post-etching were studied before and after UV irradiation for 2 h. We observed that a strong confinement effect occurred in all of the PSi samples from the blue shift of the band gap energy compared with that of crystalline Si, while the effective thermal diffusivities were almost two orders of the magnitude smaller than that of conventional Si crystals. The band gap shifted to higher energy and the effective thermal diffusivity decreased as the post-etching time increased. In the case of a PSi sample that was not chemically post-etched, the optical absorption and effective thermal diffusivity before and after UV irradiation were almost unchanged. However, for the PSi samples that were chemically post-etched, the optical absorption decreased and the effective thermal diffusivity increased after UV irradiation. This indicates that PSi samples that are post-etched are more readily affected by UV irradiation, i.e., oxidized by replacing Si-H x bonds by Si-O x, than those that do not undergo post-etching

  17. Probabilistic human health risk assessment of degradation-related chemical mixtures in heterogeneous aquifers: Risk statistics, hot spots, and preferential channels

    Science.gov (United States)

    Henri, Christopher V.; Fernández-Garcia, Daniel; Barros, Felipe P. J.

    2015-06-01

    The increasing presence of toxic chemicals released in the subsurface has led to a rapid growth of social concerns and the need to develop and employ models that can predict the impact of groundwater contamination on human health risk under uncertainty. Monitored natural attenuation is a common remediation action in many contamination cases. However, natural attenuation can lead to the production of daughter species of distinct toxicity that may pose challenges in pollution management strategies. The actual threat that these contaminants pose to human health depends on the interplay between the complex structure of the geological media and the toxicity of each pollutant byproduct. This work addresses human health risk for chemical mixtures resulting from the sequential degradation of a contaminant (such as a chlorinated solvent) under uncertainty through high-resolution three-dimensional numerical simulations. We systematically investigate the interaction between aquifer heterogeneity, flow connectivity, contaminant injection model, and chemical toxicity in the probabilistic characterization of health risk. We illustrate how chemical-specific travel times control the regime of the expected risk and its corresponding uncertainties. Results indicate conditions where preferential flow paths can favor the reduction of the overall risk of the chemical mixture. The overall human risk response to aquifer connectivity is shown to be nontrivial for multispecies transport. This nontriviality is a result of the interaction between aquifer heterogeneity and chemical toxicity. To quantify the joint effect of connectivity and toxicity in health risk, we propose a toxicity-based Damköhler number. Furthermore, we provide a statistical characterization in terms of low-order moments and the probability density function of the individual and total risks.

  18. Voltammetry at porous electrodes: A theoretical study

    OpenAIRE

    Barnes, Edward O; Chena, Xiaojun; Li, Peilin; Compton, Richard G.

    2014-01-01

    Theory is presented to simulate both chronoamperometry and cyclic voltammetry at porous electrodes fabricated by means of electro-deposition around spherical templates. A theoretical method to extract heterogeneous rate constants for quasireversible and irreversible systems is proposed by the approximation of decoupling of the diffusion within the porous electrode and of bulk diffusion to the electrode surface.

  19. MHD Flow Heat and Mass Transfer of Micropolar Fluid over a Nonlinear Stretching Sheet with Variable Micro Inertia Density, Heat Flux and Chemical Reaction in a Non-darcy Porous Medium

    OpenAIRE

    . Dr. S. Rawat; Kapoor Saurabh; Prof R Bhargava

    2016-01-01

    This paper investigates the two dimensional flow, heat and mass transfer of chemically reacting Micropolar fluid over a non-linear stretching sheet with variable heat flux in a non-darcy porous medium. The rate of chemical reaction is assumed to be constant throughout the fluid i.e. homogenous. Using a similarity transformation, the governing partial differential equations are transformed into a system of ordinary differential equation, which is then solved using Finite element me...

  20. Complexity of Soils Porous Structure: A Simple Question

    Science.gov (United States)

    Benito, R. M.; Cardenas, J. P.; Santiago, A.; Borondo, F.; Losada, J. C.; Tarquis, A. M.; Grupo de Sistemas Complejos

    2011-12-01

    In the last decades scientist have realized that soil processes are implicated the biggest global challenges facing humanity such as soil aeration, sequestration or emission of greenhouse gasses, volatilization of volatile organic chemicals among other phenomena. Progress in these challenges will depend on being able to understand the integrated behavior of soil as a system, and dealing with the complexity in describing soil in these terms. In this work we focus in one of the critical soil issues: soil structure and pore connectivity. A quantitative and explicit characterization of soil structure is difficult because of the complexity of the pore space. We proposed a model to attempt to capture the complexity of the system in which we interpret porous soils as heterogeneous networks, where pores are represented by nodes and the links representing flows between them. Pore properties such as position and size are described by fixed states in a metric space, while an affinity function is introduced to bias the attachment probabilities of links according to these properties taking in account soil texture. These types of models are named as Heterogeneous Preferential Attachment (HPA). We perform an analytical study of the degree distributions in the soil model and show that under reasonable conditions all the model variants yield a multiscaling behavior in the connectivity degrees, leaving an empirically testable signature of heterogeneity in the topology of pore networks. With the aim to study in more detail topological properties of these networks, for different real soils samples an analysis of the community structure have been applied and studied depending on the values of the parameters of the porous soil model used. The detection of communities of pores, as groups densely connected with only sparser connections between groups, could contribute to understand the mechanisms of the diffusion phenomena in soils. References Cardenas, J. P. Cardenas, A. M. Tarquis, J. C

  1. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    Directory of Open Access Journals (Sweden)

    M. De Lucia

    2014-09-01

    Full Text Available Fully-coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i that the presence of CO2 is the only driving force for chemical reactions and (ii that its migration in the reservoir is only marginally affected by immobilization due to chemical reactions. In the simplified coupling, the exposure time to CO2 of each element of the hydrodynamic grid is estimated by non-reactive simulations and the reaction path of one single batch geochemical model is applied to each grid element during its exposure time. In heterogeneous settings, analytical scaling relationships provide the dependency of velocity and amount of reactions to porosity and gas saturation. The analysis of TOUGHREACT fully coupled reactive transport simulations of CO2 injection in saline aquifer, inspired to the Ketzin pilot site (Germany, both in homogeneous and heterogeneous settings, confirms that the reaction paths predicted by fully coupled simulations in every element of the grid show a high degree of self-similarity. A threshold value for the minimum concentration of dissolved CO2 considered chemically active is showed to mitigate the effects of the discrepancy between dissolved CO2 migration in non-reactive and fully coupled simulations. In real life, the optimal threshold value is unknown and has to be estimated, e.g., by means of 1-D or 2-D simulations, resulting in an uncertainty ultimately due to the process de-coupling. However, such uncertainty is more than acceptable given that the alternative coupling enables using grids in the order of million elements, profiting from much better description of heterogeneous reservoirs at a fraction of the calculation time of fully coupled models.

  2. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    Science.gov (United States)

    De Lucia, M.; Kempka, T.; Kühn, M.

    2015-02-01

    Fully coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i) that the presence of CO2 is the only driving force for chemical reactions and (ii) that its migration in the reservoir is only marginally affected by immobilisation due to chemical reactions. In the simplified coupling, the exposure time to CO2 of each element of the hydrodynamic grid is estimated by non-reactive simulations and the reaction path of one single batch geochemical model is applied to each grid element during its exposure time. In heterogeneous settings, analytical scaling relationships provide the dependency of velocity and amount of reactions to porosity and gas saturation. The analysis of TOUGHREACT fully coupled reactive transport simulations of CO2 injection in saline aquifer, inspired to the Ketzin pilot site (Germany), both in homogeneous and heterogeneous settings, confirms that the reaction paths predicted by fully coupled simulations in every element of the grid show a high degree of self-similarity. A threshold value for the minimum concentration of dissolved CO2 considered chemically active is shown to mitigate the effects of the discrepancy between dissolved CO2 migration in non-reactive and fully coupled simulations. In real life, the optimal threshold value is unknown and has to be estimated, e.g. by means of 1-D or 2-D simulations, resulting in an uncertainty ultimately due to the process de-coupling. However, such uncertainty is more than acceptable given that the alternative coupling enables using grids of the order of millions of elements, profiting from much better description of heterogeneous reservoirs at a fraction of the calculation time of fully coupled models.

  3. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    Directory of Open Access Journals (Sweden)

    M. De Lucia

    2015-02-01

    Full Text Available Fully coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i that the presence of CO2 is the only driving force for chemical reactions and (ii that its migration in the reservoir is only marginally affected by immobilisation due to chemical reactions. In the simplified coupling, the exposure time to CO2 of each element of the hydrodynamic grid is estimated by non-reactive simulations and the reaction path of one single batch geochemical model is applied to each grid element during its exposure time. In heterogeneous settings, analytical scaling relationships provide the dependency of velocity and amount of reactions to porosity and gas saturation. The analysis of TOUGHREACT fully coupled reactive transport simulations of CO2 injection in saline aquifer, inspired to the Ketzin pilot site (Germany, both in homogeneous and heterogeneous settings, confirms that the reaction paths predicted by fully coupled simulations in every element of the grid show a high degree of self-similarity. A threshold value for the minimum concentration of dissolved CO2 considered chemically active is shown to mitigate the effects of the discrepancy between dissolved CO2 migration in non-reactive and fully coupled simulations. In real life, the optimal threshold value is unknown and has to be estimated, e.g. by means of 1-D or 2-D simulations, resulting in an uncertainty ultimately due to the process de-coupling. However, such uncertainty is more than acceptable given that the alternative coupling enables using grids of the order of millions of elements, profiting from much better description of heterogeneous reservoirs at a fraction of the calculation time of fully coupled models.

  4. Heterogeneous adsorption and catalytic oxidation of benzene, toluene and xylene over spent and chemically regenerated platinum catalyst supported on activated carbon

    Science.gov (United States)

    Shim, Wang Geun; Kim, Sang Chai

    2010-06-01

    The heterogeneous adsorption and catalytic oxidation of benzene, toluene and o-xylene (BTX) over the spent platinum catalyst supported on activated carbon (Pt/AC) as well as the chemically treated spent catalysts were studied to understand their catalytic and adsorption activities. Sulfuric aqueous acid solution (0.1N, H 2SO 4) was used to regenerate the spent Pt/AC catalyst. The physico-chemical properties of the catalysts in the spent and chemically treated states were analyzed by using nitrogen adsorption-desorption isotherm and elemental analysis (EDX). The gravimetric adsorption and the light-off curve analysis were employed to study the BTX adsorption and oxidation on the spent catalyst and its modified Pt/AC catalysts. The experimental results indicate that the spent Pt/AC catalyst treated with the H 2SO 4 aqueous solution has a higher toluene adsorption and conversion ability than that of the spent Pt/AC catalyst. A further studies of H 2SO 4 treated Pt/AC catalyst on their catalytic and heterogeneous adsorption behaviours for BTX revealed that the activity of the H 2SO 4 treated Pt/AC catalyst follows the sequence of benzene > toluene > o-xylene. The adsorption equilibrium isotherms of BTX on the H 2SO 4 treated Pt/AC were measured at different temperatures ranging from 120 to 180 °C. To correlate the equilibrium data and evaluate their adsorption affinity for BTX, the two sites localized Langmuir (L2m) isotherm model was employed. The heterogeneous surface feature of the H 2SO 4 treated Pt/AC was described in detail with the information obtained from the results of isosteric enthalpy of adsorption and adsorption energy distributions. Furthermore, the activity of H 2SO 4 treated Pt/AC about BTX was found to be directly related to the Henry's constant, isosteric enthalpy of adsorption and adsorption energy distribution functions.

  5. Homochiral porous metal-organic frameworks: Why and how?

    International Nuclear Information System (INIS)

    This paper highlights the most significant recent advances in the synthesis, characterization, and applications of single-crystalline homochiral porous metal-organic frameworks (MOFs). The motivations for the synthesis of homochiral porous solids and the strategies on how they can be designed are provided. The latest examples of chiral separation and Lewis acid heterogeneous asymmetric catalysis using homochiral porous MOFs are presented

  6. Non-equilibrium thermo-chemical heat storage in porous media: Part 2 – A 1D computational model for a calcium hydroxide reaction system

    International Nuclear Information System (INIS)

    Thermal energy storage technologies can facilitate the transition to an energy system based largely on renewable sources and enable efficiency gains for industrial processes in general. Due to their specific advantages, various concepts of thermo-chemical storage systems are being developed. They share characteristic features of mass and heat transport that are strongly coupled through a variety of physical and chemical phenomena. To facilitate the understanding of the coupled multi-physics processes inside such systems, a versatile conceptual model for directly permeated reactive beds was developed in part 1 of this work. It was based on thermodynamic principles and the Theory of Porous Media. The model was then implemented into OpenGeoSys, a scientific finite element simulation software. In this article, the model is specified to the well-studied calcium hydroxide reaction system to illustrate its practical applicability. Sensitivity analyses reveal the influence of particle diameter, porosity, permeability, mass flux, and reaction rate. Two distinct “reaction waves” are identified to migrate through the reactor. The power required to pump the gas stream was decomposed into parts related to the classical mechanical pressure drop and to the chemical reaction. The results can be used for the optimization of thermochemical heat storage systems. - Highlights: • Detailed investigation of coupled multiphysics in thermochemical heat storage. • Thermodynamically consistent model for thermochemical heat storage systems. • Analysis of thermal power depending on material and process parameters. • Two reaction waves are identified that traverse the reactor. • Mechanical pumping power splits into mechanically and chemically induced parts

  7. Improvement of solar cells performances by surface passivation using porous silicon chemically treated with LiBr solution

    Energy Technology Data Exchange (ETDEWEB)

    Haddadi, Ikbel; Dimassi, Wissem; Bousbih, Rabaa; Hajji, Massoud; Kanzari, M. Ali; Ezzaouia, Hatem [Laboratoire de Photovoltaique, Centre de Recherche et des Technologies de l' Energie, Hammam Lif (Tunisia)

    2011-03-15

    Solar cells need efficient light absorption to achieve high efficiencies. In this paper, we present a study on the immersion effect of porous silicon (PS) in a Lithium Bromide (LiBr) aqueous solution, followed by thermal annealing at 100 C for 30 min under nitrogen atmosphere on solar cells performances. The surface morphology was studied by Atomic Force Microscopy (AFM). All samples were analyzed by Fourier transmission infrared spectroscopy (FTIR) before and after LiBr immersion. Good electrical properties were observed after thermal annealing at 100 C for 30 min under nitrogen atmosphere. The reflection spectra of PS, before and after LiBr treatment, performed in the 300-1200 nm wavelength range, showed an important decrease of the reflectivity by this new treatment. A significant increase of the photoluminescence (PL) intensity was obtained after LiBr treatment. An enhancement of the light beam induced current (LBIC) as well as the internal quantum efficiency (IQE) were shown after LiBr treatment. I-V characteristics, under AM1.5 illumination, were improved owing to the increase of the minority carrier diffusion length (L) and an excellent enhancement of the surface recombination velocity (V{sub s}) (copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Study the effect of chemical reaction and variable viscosity on free convection MHD radiating flow over an inclined plate bounded by porous medium

    Science.gov (United States)

    Ali, M.; Alim, M. A.; Nasrin, R.; Alam, M. S.

    2016-07-01

    An analysis is performed to study the free convection heat and mass transfer flow of an electrically conducting incompressible viscous fluid about a semi-infinite inclined porous plate under the action of radiation, chemical reaction in presence of magnetic field with variable viscosity. The dimensionless governing equations are steady, two-dimensional coupled and non-linear ordinary differential equation. Nachtsgeim-Swigert shooting iteration technique along with Runge-Kutta integration scheme is used to solve the non-dimensional governing equations. The effects of magnetic parameter, viscosity parameter and chemical reaction parameter on velocity, temperature and concentration profiles are discussed numerically and shown graphically. Therefore, the results of velocity profile decreases for increasing values of magnetic parameter and viscosity parameter but there is no effect for reaction parameter. The temperature profile decreases in presence of magnetic parameter, viscosity parameter and Prandtl number but increases for radiation parameter. Also, concentration profile decreases for the increasing values of magnetic parameter, viscosity parameter and reaction parameter. All numerical calculations are done with respect to salt water and fixed angle of inclination of the plate.

  9. Percolation in Heterogeneous Media

    International Nuclear Information System (INIS)

    This work is a theoretical reflection on the problematic of the modeling of heterogeneous media, that is on the way of their simple representation conserving their characteristic features. Two particular problems are addressed in this thesis. Firstly, we study the transport in porous media, that is in a heterogeneous media which structure is quenched. A pore space is represented in a simple way - a pore is symbolized as a tube of a given length and a given diameter. The fact that the correlations in the distribution of pore sizes are taken into account by a construction of a hierarchical network makes possible the modeling of porous media with a porosity distributed over several length scales. The transport in the hierarchical network shows qualitatively different phenomena from those observed in simpler models. A comparison of numerical results with experimental data shows that the hierarchical network gives a good qualitative representation of the structure of real porous media. Secondly, we study a problem of the transport in a heterogeneous media which structure is evolving during the time. The models where the evolution of the structure is not influenced by the transport are studied in detail. These models present a phase transition of the same nature as that observed on the percolation networks. We propose a new theoretical description of this transition, and we express critical exponents describing the evolution of the conductivity as a function of fundamental exponents of percolation theory. (author)

  10. Ionic Diffusion and Kinetic Homogeneous Chemical Reactions in the Pore Solution of Porous Materials with Moisture Transport

    DEFF Research Database (Denmark)

    Johannesson, Björn

    2009-01-01

    ’s law of diffusion and the generalized Darcy’s law will be used together with derived constitutive equations for chemical reactions within phases. The mass balance equations for the constituents and the phases together with the constitutive equations gives the coupled set of non-linear differential...... general description of chemical reactions among constituents is described. The Petrov – Galerkin approach are used in favour of the standard Galerkin weighting in order to improve the solution when the convective part of the problem is dominant. A modified type of Newton – Raphson scheme is derived for...

  11. Effect of age and chemical treatments on characteristic parameters for active and porous sublayers of polymeric composite membranes.

    Science.gov (United States)

    Benavente, J; Vázquez, M I

    2004-05-15

    Changes in the transport parameters and the chemical nature of the surface of composite polyamide/polysulfone membranes due to both aging and treatment with chemical products (HCl, H(3)NO, and NaOH) have been considered. Hydraulic and salt permeability were obtained from water flow and salt diffusion measurements, respectively, and their values seem to indicate a modification in the structural parameters (porosity/thickness) of aging samples, while HCl and HNO(3) treatments will act in the opposite way. Chemical modifications in the membrane surfaces were studied by X-ray photoelectron spectroscopy (XPS), which mainly show the effect of H(3)NO and HCl on the polyamide active layer of the membranes (polyamide oxidation), but no chemical damage for that sublayer. Electrical characterization of both sublayers of the composite membranes were determined from impedance spectroscopy (IS) measurements using equivalent circuits as models, and these results indicate: (i) a strong increase of the membrane electrical resistance as a consequence of aging, mainly that associated with the active sublayer (30 times higher for an old sample than for a fresh one) and treatment with NaOH; (ii) the reduction of this effect when the samples were treated with HCl and HNO(3) solutions. Changes in the values of the electrical resistance of the composite membranes are in agreement with those obtained for permeabilities, but the electrical parameter also allows the determination of the contribution of each sublayer. PMID:15082393

  12. Solute transport through porous media using asymptotic dispersivity

    Indian Academy of Sciences (India)

    P K Sharma; Teodrose Atnafu Abgaze

    2015-08-01

    In this paper, multiprocess non-equilibrium transport equation has been used, which accounts for both physical and chemical non-equilibrium for reactive transport through porous media. An asymptotic distance dependent dispersivity is used to embrace the concept of scale-dependent dispersion for solute transport in heterogeneous porous media. Semi-analytical solution has been derived of the governing equations with an asymptotic distance dependent dispersivity by using Laplace transform technique and the power series method. For application of analytical model, we simulated observed experimental breakthrough curves from 1500 cm long soil column experiments conducted in the laboratory. The simulation results of break-through curves were found to deviate from the observed breakthrough curves for both mobile–immobile and multiprocess non-equilibrium transport with constant dispersion models. However, multiprocess non-equilibrium with an asymptotic dispersion model gives better fit of experimental breakthrough curves through long soil column and hence it is more useful for describing anomalous solute transport through hetero-geneous porous media. The present model is simpler than the stochastic numerical method.

  13. Radiative heat transfer to steady flow of a chemically reacting fluid in a horizontal porous channel with variable wall temperature

    International Nuclear Information System (INIS)

    Fluid motion in a horizontal channel at very high temperatures is studied when the radiative heat flux is expressible in general differential form. On the assumption that the fluid is chemically reacting while the temperatures of the channel walls vary linearly with axial distance, the problem is reduced to a set of coupled nonlinear ordinary integro-differential equations when only linear terms in the axial distance are retained. An iterative sequence is established in which the eventual linear equations are discretized by employing finite differences for derivatives and trapazium rule for integrals. The effect of the chemical rate constant and the radiative parameters on the flow are discussed. (author). 5 refs, 2 figs

  14. Chemical characteristics of ice residual nuclei in anvil cirrus clouds: evidence for homogeneous and heterogeneous ice formation

    Directory of Open Access Journals (Sweden)

    C. H. Twohy

    2005-01-01

    Full Text Available A counterflow virtual impactor was used to collect residual particles larger than about 0.1 μm diameter from anvil cirrus clouds generated over Florida in the southern United States. A wide variety of particle types were found. About one-third of the nuclei were salts, with varying amounts of crustal material, industrial metals, carbonaceous particles, and sulfates. Ambient aerosol particles near the anvils were found to have similar compositions, indicating that anvils act to redistribute particles over large regions of the atmosphere. Sampling occurred at a range of altitudes spanning temperatures from −21 to −56°C. More insoluble (crustal and metallic particles typical of heterogeneous ice nuclei were found in ice crystals at warmer temperatures, while more soluble salts and sulfates were present at cold temperatures. At temperatures below about −35 to −40°C, soluble nuclei outnumbered insoluble nuclei, evidently reflecting the transition from primarily heterogeneous to primarily homogeneous freezing as a source of anvil ice.

  15. Dilution and reactive mixing in three-dimensional helical flows in porous media

    Science.gov (United States)

    Chiogna, Gabriele; Ye, Yu; Grathwohl, Peter; Cirpka, Olaf A.; Rolle, Massimo

    2016-04-01

    Dilution under steady-state flow and transport conditions in porous media occurs primarily by lateral mass exchange at the fringe of solute plumes. This process controls the fate and transport of scalars in groundwater and in chemical reactors and it is fundamental for the understanding of many reactive processes. Three-dimensional flow fields can be characterized by a complex topological structure, which may greatly influence dilution and dilution enhancement of dissolved plumes, which is quantified by the exponential of the Shannon entropy [1]. In previous works, we identified the necessary conditions to obtain helical flow fields in non-stationary anisotropic heterogeneous porous media [2, 3]. To prove our theoretical findings, we perform steady-state bench-scale experiments with a conservative tracer and we provide a model-based investigation of the results [4]. The relevance of transverse mixing enhancement for the case of reactive solute transport is computed numerically using, as metrics of mixing, the length of a reactive plume undergoing an instantaneous complete bimolecular reaction and its critical dilution index. [1] Cirpka O.A., Chiogna G., Rolle M. and A. Bellin (2015). Transverse mixing in three-dimensional non-stationary anisotropic heterogeneous porous media. Water Resources Research, 51, DOI: 10.1002/2014WR015331. [2] Chiogna G., Cirpka O.A., Rolle M. and A. Bellin (2015). Helical flow streamlines in three-dimensional nonstationary anisotropic heterogeneous porous media. Water Resources Research, 51, DOI:10.1002/2014WR015330. [3] Chiogna G., Rolle M., Bellin A. and O.A. Cirpka (2014). Helicity and flow topology in three dimensional porous media. Advances in Water Resources, 73, 134-143, DOI: 10.1016/j.advwatres.2014.06.017. [4] Ye Y., Chiogna G., Cirpka O.A., Grathwohl P., and M. Rolle (2015). Experimental evidence of helical flow in porous media. Phys. Rev. Lett., 115, 194502, DOI: 10.1103/PhysRevLett.115.194502

  16. Chemical synthesis of magnetic nanocrystals: Recent progress

    International Nuclear Information System (INIS)

    Colloidal chemical synthesis of various types of magnetic nanocrystals is discussed with regard to recent discoveries. We first outline the chemical preparation of single-component magnetic nanocrystals with controlled size, shape, and uniformity based on several solution-phase methods, especially thermal decomposition and/or reduction method. Then we discuss the synthetic strategies of multi-component nanocrystals incorporating at least one magnetic component by manipulating heterogeneous nucleation and growth process. Toward the end, approaches for preparing hollow/porous magnetic nanocrystals are highlighted. We believe that the summarized chemical synthesis will pave the way for the future development of extraordinary magnetic nanocrystals. (topical review - magnetism, magnetic materials, and interdisciplinary research)

  17. Convection in Porous Media

    CERN Document Server

    Nield, Donald A

    2013-01-01

    Convection in Porous Media, 4th Edition, provides a user-friendly introduction to the subject, covering a wide range of topics, such as fibrous insulation, geological strata, and catalytic reactors. The presentation is self-contained, requiring only routine mathematics and the basic elements of fluid mechanics and heat transfer. The book will be of use not only to researchers and practicing engineers as a review and reference, but also to graduate students and others entering the field. The new edition features approximately 1,750 new references and covers current research in nanofluids, cellular porous materials, strong heterogeneity, pulsating flow, and more. Recognized as the standard reference in the field Includes a comprehensive, 250-page reference list Cited over 2300 times to date in its various editions Serves as an introduction for those entering the field and as a comprehensive reference for experienced researchers Features new sections on nanofluids, carbon dioxide sequestration, and applications...

  18. Particle dispersion and deposition in porous media: a computational perspective

    Science.gov (United States)

    Boccardo, Gianluca; Crevacore, Eleonora; Sethi, Rajandrea; Marchisio, Daniele

    2015-11-01

    This work investigates particle dispersion in porous media, which is of central relevance in a number of applications ranging from groundwater remediation tochemical engineering. The challenge lies in studying the complex fluid dynamics behavior arising at the microscale (very difficult to observe experimentally) and obtaining transport models to be employed at the macroscopic scale of interest. While a wealth of studies have approached this problem, the case of particle transport with a concurrent heterogeneous chemical reaction (e.g.: particle deposition) still lacks a satisfactory description, especially when considering a polydisperse population of solid particles. Moreover, the oft-used simplified descriptions of the porous medium (via array of spheres or similar strategies) fail to fully take into account the effect of the packing structure. Our novel approach relies on an ``in-silico'' procedure where many 3-D realistic porous media models are constructed via rigid-body simulations and fluid flowand particle transport are then investigated through computational fluid dynamics. The results evidence the need for a deeper look, afforded by these methodology, into the influence of the features of realistic porous media on particle transport and deposition.

  19. Soft chemical synthesis of carbon-modified Ti3+ self-doped hierarchical porous TiO2 with enhanced photocatalysis

    Science.gov (United States)

    Zhao, Chunxia; Wang, Zongsheng; Chen, Wen; Song, Yanbao; Chen, Xuehua; Xie, Tao

    2016-03-01

    Carbon-modified Ti3+ self-doped hierarchical porous titanium dioxides were synthesized by one-step soft chemical method. The contents of carbon and Ti3+ of the catalysts were tuned through a facile heat treatment. The prepared photocatalysts possess well-packed uniform macropores with the size of ˜200nm, mesoporous structure with the pore size of 5.9-6.8nm, and the specific surface area of 50-200m2/g. The results illustrate the carbon combined with TiO2 via the interfacial C‑O‑Ti bonds and the rich existence of Ti3+. The catalyst with 18wt.% carbon content exhibits a degradation ratio of crystal violet up to 97.5%. The enhanced photocatalysis is ascribed to the synergistic effect of carbon and Ti3+. The interfacial C‑O‑Ti bonds act as the pathway to transfer excited electrons and the Ti3+ can trap the electrons to hinder the recombination of electrons and holes.

  20. Combined Influence of Thermal Diffusion and Diffusion Thermo on Unsteady MHD Free Convective Fluid Flow Past an Infinite Vertical Porous Plate in Presence of Chemical Reaction

    Science.gov (United States)

    Srinivasa Raju, Rallabandi

    2016-06-01

    The present investigation is concerned with the effects of thermal diffusion (Soret) and diffusion thermo (Dufour) on an unsteady MHD free convective flow with heat and mass transfer of an electrically conducting fluid in the presence of chemical reaction. A uniform magnetic field acts perpendicular to the porous surface, which absorbs the fluid with a suction velocity varying with time. The problem is governed by coupled non-linear partial differential equations with appropriate boundary conditions. A finite element numerical solution is developed to solve the resulting well-posed two-point boundary value problem. The present numerical results are compared with available data and are found in an excellent agreement. The expressions for velocity, temperature and concentration fields are obtained. With the aid of these, the expressions for the coefficient of skin-friction, the rate of heat transfer in the form of Nusselt number and the rate of mass transfer in the form of Sherwood number are derived. Finally the effects of various physical parameters of the flow quantities are studied with the help of graphs and tables.

  1. Preparation of core–shell porous magnetite@carbon nanospheres through chemical vapor deposition as anode materials for lithium-ion batteries

    International Nuclear Information System (INIS)

    Highlights: • Fe3O4/C composites are prepared through hydrothermal treatment and subsequent CVD. • Monodispersed core–shell Fe3O4@C nanospheres are connected with 3D carbon networks. • Fe3O4@C composites exhibit high reversible capacity and excellent rate capability. - Abstract: Monodispersed core-shell porous Fe3O4@C nanospheres are prepared through hydrothermal treatment and subsequent chemical vapor deposition (CVD). Specially, the magnetite reduction and carbon coating are completed via CVD simultaneously and the process is verified by X-ray diffraction, scanning electron microscope and transmission electron microscope. Fe3O4@C composites exhibit high reversible capacity (∼1100 mA h g−1 at 100 mA g−1 after 60 cycles), excellent cyclic stability and good rate performance. The carbon coating layer serves as a highly conducting framework and provides a flexible space for buffering strain and stress, and the pores facilitate ion transport during electrochemical cycling. More importantly, the core-shell Fe3O4@C composite is connected by carbon to form a three-dimensional network, which contributes to the relief of inner strain and the fast transport of electrons and lithium ions

  2. Heterogeneous Photocatalysis and Photoelectrocatalysis: From Unselective Abatement of Noxious Species to Selective Production of High-Value Chemicals.

    Science.gov (United States)

    Augugliaro, Vincenzo; Camera-Roda, Giovanni; Loddo, Vittorio; Palmisano, Giovanni; Palmisano, Leonardo; Soria, Javier; Yurdakal, Sedat

    2015-05-21

    Heterogeneous photocatalysis and photoelectrocatalysis have been considered as oxidation technologies to abate unselectively noxious species. This article focuses instead on the utilization of these methods for selective syntheses of organic molecules. Some promising reactions have been reported in the presence of various TiO2 samples and the important role played by the amorphous phase has been discussed. The low solubility of most of the organic compounds in water limits the utilization of photocatalysis. Dimethyl carbonate has been proposed as an alternative green organic solvent. The recovery of the products by coupling photocatalysis with pervaporation membrane technology seems to be a solution for future industrial applications. As far as photoelectrocatalysis is concerned, a decrease in recombination of the photogenerated pairs occurs, enhancing the rate of the oxidation reactions and the quantum yield. Another benefit is to avoid reaction(s) between the intermediates and the substrate, as anodic and cathodic reactions take place in different places. PMID:26263277

  3. Automated separation for heterogeneous immunoassays

    OpenAIRE

    Truchaud, A.; Barclay, J; Yvert, J. P.; Capolaghi, B.

    1991-01-01

    Beside general requirements for modern automated systems, immunoassay automation involves specific requirements as a separation step for heterogeneous immunoassays. Systems are designed according to the solid phase selected: dedicated or open robots for coated tubes and wells, systems nearly similar to chemistry analysers in the case of magnetic particles, and a completely original design for those using porous and film materials.

  4. Optical Characteristics of Porous Glasses Matrix and Its Light-conducted Mechanism

    Institute of Scientific and Technical Information of China (English)

    GUO Li-ping; CHEN Yong-xi; LI Ying-xia; LEI Jia-heng; LIU Wei; XIONG Hong-chao

    2004-01-01

    The optical properties of matrix of porous glasses and phase-separated glasses were investigated by visible spectroscopy and infrared spectroscopy. The experimental results show that, both the porous glasses and phase-separated glasses have very good light transmission in visible light region that wavelenth is longer than 560nm. The micropores of porous glasses and the boron-rich phase of phase-separated glasses have strong Rayleigh scatter effects on the visible light, the largest scatter occurrs at 360-370nm; the thicker the glasses, the larger the light scattering. Thus, the pore size distribution and the size of heterogeneous micro zone in boron-rich phase of phase-separated glasses can be measured. After coupled into porours glasses, the most intense absorption of hydrated ions of [Co(H2O)6]2+ shifts from 508nm to 515nm. The production of the most intense absorption and the red shift were owed to Jahn-Teller effect of octahedral field formed by six H2O molecular and perturbation effect resulted by microporous of porous glasses for its physics-chemical circumstance. As a result, the porous glasses are perfect optical function materials in visible region, which can be assembled by chemical method.

  5. OpenGeoSys: An Open-Source Initiative for Numerical Simulation of Thermo-Hydro-Mechanical/Chemical (THM/C) Processes in Porous Media

    Science.gov (United States)

    Watanabe, N.; Bilke, L.; Fischer, T.; Kalbacher, T.; Nagel, T.; Naumov, D.; Rink, K.; Shao, H.; Wang, W.; Kolditz, O.

    2014-12-01

    In this paper we describe the OpenGeoSys (OGS) project, which is a scientific open-source initiative for numerical simulations of thermo-hydro-mechanical/chemical processes in fractured porous media. The basic concept is to provide a flexible numerical framework (using primarily the Finite Element Method (FEM)) for solving multi-field problems in porous and fractured media for applications in geoscience, hydrology and energy conversion. To this purpose OGS is based on an object-oriented (OO) FEM concept including a broad spectrum of interfaces for pre- and post-processing. OGS has been developed since the mid-eighties, has been continuously improved in concept and evolved through Fortran, C, and C++ implementations. The idea behind OGS is to provide an open platform to the scientific community featuring professional software-engineering tools such as platform-independent compiling and automated benchmarking. Comprehensive benchmarking books (Kolditz et al. 2012, 2014) and tutorials (Sachse et al. 2014) are being published. Benchmarking has proven to be a valuable tool for cooperation between different developer teams, for example, for code comparison and validation purposes (DEVOVALEX, CO2 BENCH and SSBENCH projects). The computational efficiency of OO codes is very important in scientific computing (Wang et al. 2009). We have already parallelized the OO codes by using both custom schemes and the PETSc library (Wang et al. 2014). Meanwhile the 6th version, ogs6, is under construction to further foster various parallel computing techniques and to improve code modularity for enhancing collaborative development by several researchers. The code is openly accessible via GitHub (https://github.com/ufz/ogs) and our development workflow extensively builds on Git features such as branching, merging automatic compiling, executing unit tests and code review to improve communication among developers and maintain code quality. OGS also provides a graphical user interface (Data

  6. Mixed convective MHD flow of a micropolar fluid with ohmic heating, radiation and viscous dissipation over a chemically reacting porous plate subjected to a constant heat flux and concentration gradient

    OpenAIRE

    Kumar Hitesh

    2014-01-01

    In the present paper analysis of a chemically reacting mixed convection MHD micropolar flow, heat and mass transfer in porous medium with the effects of ohmic heating, radiation and viscous dissipation past an infinite vertical plate which is subjected to a constant heat flux and the concentration gradient. The non-linear coupled partial differential equations are solved numerically using an implicit finite difference scheme known as Keller-box method. The ...

  7. The Effects of Variable Viscosity, Viscous Dissipation and Chemical Reaction on Heat and Mass Transfer Flow of MHD Micropolar Fluid along a Permeable Stretching Sheet in a Non-Darcian Porous Medium

    OpenAIRE

    Salem, A. M.

    2013-01-01

    A numerical model is developed to study the effects of temperature-dependent viscosity on heat and mass transfer flow of magnetohydrodynamic(MHD) micropolar fluids with medium molecular weight along a permeable stretching surface embedded in a non-Darcian porous medium in the presence of viscous dissipation and chemical reaction. The governing boundary equations for momentum, angular momentum (microrotation), and energy and mass transfer are transformed to a set of nonlinear ordinary differen...

  8. Physico-Chemical Heterogeneity of Organic-Rich Sediments in the Rifle Aquifer, CO: Impact on Uranium Biogeochemistry.

    Science.gov (United States)

    Janot, Noémie; Lezama Pacheco, Juan S; Pham, Don Q; O'Brien, Timothy M; Hausladen, Debra; Noël, Vincent; Lallier, Florent; Maher, Kate; Fendorf, Scott; Williams, Kenneth H; Long, Philip E; Bargar, John R

    2016-01-01

    The Rifle alluvial aquifer along the Colorado River in west central Colorado contains fine-grained, diffusion-limited sediment lenses that are substantially enriched in organic carbon and sulfides, as well as uranium, from previous milling operations. These naturally reduced zones (NRZs) coincide spatially with a persistent uranium groundwater plume. There is concern that uranium release from NRZs is contributing to plume persistence or will do so in the future. To better define the physical extent, heterogeneity and biogeochemistry of these NRZs, we investigated sediment cores from five neighboring wells. The main NRZ body exhibited uranium concentrations up to 100 mg/kg U as U(IV) and contains ca. 286 g of U in total. Uranium accumulated only in areas where organic carbon and reduced sulfur (as iron sulfides) were present, emphasizing the importance of sulfate-reducing conditions to uranium retention and the essential role of organic matter. NRZs further exhibited centimeter-scale variations in both redox status and particle size. Mackinawite, greigite, pyrite and sulfate coexist in the sediments, indicating that dynamic redox cycling occurs within NRZs and that their internal portions can be seasonally oxidized. We show that oxidative U(VI) release to the aquifer has the potential to sustain a groundwater contaminant plume for centuries. NRZs, known to exist in other uranium-contaminated aquifers, may be regionally important to uranium persistence. PMID:26651843

  9. Untangling the Chemical Evolution of Titan's Atmosphere and Surface -- From Homogeneous to Heterogeneous Chemistry

    Energy Technology Data Exchange (ETDEWEB)

    Kaiser, Ralf I.; Maksyutenko, Pavlo; Ennis, Courtney; Zhang, Fangtong; Gu, Xibin; Krishtal, Sergey P.; Mebel, Alexander M.; Kostko, Oleg; Ahmed, Musahid

    2010-03-16

    The arrival of the Cassini-Huygens probe at Saturn's moon Titan - the only Solar System body besides Earth and Venus with a solid surface and a thick atmosphere with a pressure of 1.4 atm at surface level - in 2004 opened up a new chapter in the history of Solar System exploration. The mission revealed Titan as a world with striking Earth-like landscapes involving hydrocarbon lakes and seas as well as sand dunes and lava-like features interspersed with craters and icy mountains of hitherto unknown chemical composition. The discovery of a dynamic atmosphere and active weather system illustrates further the similarities between Titan and Earth. The aerosol-based haze layers, which give Titan its orange-brownish color, are not only Titan's most prominent optically visible features, but also play a crucial role in determining Titan's thermal structure and chemistry. These smog-like haze layers are thought to be very similar to those that were present in Earth's atmosphere before life developed more than 3.8 billion years ago, absorbing the destructive ultraviolet radiation from the Sun, thus acting as 'prebiotic ozone' to preserve astrobiologically important molecules on Titan. Compared to Earth, Titan's low surface temperature of 94 K and the absence of liquid water preclude the evolution of biological chemistry as we know it. Exactly because of these low temperatures, Titan provides us with a unique prebiotic 'atmospheric laboratory' yielding vital clues - at the frozen stage - on the likely chemical composition of the atmosphere of the primitive Earth. However, the underlying chemical processes, which initiate the haze formation from simple molecules, have been not understood well to date.

  10. Spatially orthogonal chemical functionalization of a hierarchical pore network for catalytic cascade reactions

    Science.gov (United States)

    Parlett, Christopher M. A.; Isaacs, Mark A.; Beaumont, Simon K.; Bingham, Laura M.; Hondow, Nicole S.; Wilson, Karen; Lee, Adam F.

    2016-02-01

    The chemical functionality within porous architectures dictates their performance as heterogeneous catalysts; however, synthetic routes to control the spatial distribution of individual functions within porous solids are limited. Here we report the fabrication of spatially orthogonal bifunctional porous catalysts, through the stepwise template removal and chemical functionalization of an interconnected silica framework. Selective removal of polystyrene nanosphere templates from a lyotropic liquid crystal-templated silica sol-gel matrix, followed by extraction of the liquid crystal template, affords a hierarchical macroporous-mesoporous architecture. Decoupling of the individual template extractions allows independent functionalization of macropore and mesopore networks on the basis of chemical and/or size specificity. Spatial compartmentalization of, and directed molecular transport between, chemical functionalities affords control over the reaction sequence in catalytic cascades; herein illustrated by the Pd/Pt-catalysed oxidation of cinnamyl alcohol to cinnamic acid. We anticipate that our methodology will prompt further design of multifunctional materials comprising spatially compartmentalized functions.

  11. Computational Modeling of Heterogeneous Reactive Materials at the Mesoscale

    Energy Technology Data Exchange (ETDEWEB)

    BAER, MARVIN R.

    1999-09-22

    The mesoscopic processes of consolidation, deformation and reaction of shocked porous energetic materials are studied using shock physics analysis of impact on a collection of discrete ''crystals.'' Highly resolved three-dimensional CTH simulations indicate that rapid deformation occurs at material contact points causing large amplitude fluctuations of stress states with wavelengths of the order of several particle diameters. Localization of energy produces ''hot-spots'' due to shock focusing and plastic work near internal boundaries as material flows into interstitial regions. Numerical experiments indicate that ''hot-spots'' are strongly influenced by multiple crystal interactions. Chemical reaction processes also produce multiple wave structures associated with particle distribution effects. This study provides new insights into the micromechanical behavior of heterogeneous energetic materials strongly suggesting that initiation and sustained reaction of shocked heterogeneous materials involves states distinctly different from single jump state descriptions.

  12. XANES and IR spectroscopy study of the electronic structure and chemical composition of porous silicon on n- and p-type substrates

    Energy Technology Data Exchange (ETDEWEB)

    Lenshin, A. S., E-mail: lenshinas@phys.vsu.ru; Kashkarov, V. M.; Seredin, P. V. [Voronezh State University (Russian Federation); Spivak, Yu. M.; Moshnikov, V. A. [LETI St. Petersburg State Electrotechnical University (Russian Federation)

    2011-09-15

    The differences in the electronic structure and composition of porous silicon samples obtained under identical conditions of electrochemical etching on the most commonly used n- and p-type substrates with different conductivities are demonstrated by X-ray absorption near-edge spectroscopy (XANES) and Fourier transform IR spectroscopy (FTIR) methods. It is shown that significantly higher oxidation and saturation with hydrogen is observed for the porous layer on n-type substrates.

  13. XANES and IR spectroscopy study of the electronic structure and chemical composition of porous silicon on n- and p-type substrates

    International Nuclear Information System (INIS)

    The differences in the electronic structure and composition of porous silicon samples obtained under identical conditions of electrochemical etching on the most commonly used n- and p-type substrates with different conductivities are demonstrated by X-ray absorption near-edge spectroscopy (XANES) and Fourier transform IR spectroscopy (FTIR) methods. It is shown that significantly higher oxidation and saturation with hydrogen is observed for the porous layer on n-type substrates.

  14. Sequence heterogeneity of cannabidiolic- and tetrahydrocannabinolic acid-synthase in Cannabis sativa L. and its relationship with chemical phenotype.

    Science.gov (United States)

    Onofri, Chiara; de Meijer, Etienne P M; Mandolino, Giuseppe

    2015-08-01

    Sequence variants of THCA- and CBDA-synthases were isolated from different Cannabis sativa L. strains expressing various wild-type and mutant chemical phenotypes (chemotypes). Expressed and complete sequences were obtained from mature inflorescences. Each strain was shown to have a different specificity and/or ability to convert the precursor CBGA into CBDA and/or THCA type products. The comparison of the expressed sequences led to the identification of different mutations, all of them due to SNPs. These SNPs were found to relate to the cannabinoid composition of the inflorescence at maturity and are therefore proposed to have a functional significance. The amount of variation was found to be higher within the CBDAS sequence family than in the THCAS family, suggesting a more recent evolution of THCA-forming enzymes from the CBDAS group. We therefore consider CBDAS as the ancestral type of these synthases. PMID:25865737

  15. Three-dimensional simulation of chemically reacting gas flows in the porous support structure of an integrated-planar solid oxide fuel cell

    Energy Technology Data Exchange (ETDEWEB)

    Haberman, B.A.; Young, J.B. [Cambridge Univ., Engineering Dept., Cambridge (United Kingdom)

    2004-08-01

    The behaviour of an integrated-planar solid oxide fuel cell (IP-SOFC) strongly depends on the reactive diffusive flows within its porous support structure. Fuel is transported through the porous structure to the anodes of the electrochemical cells and the structure may be impregnated with the required catalysts for the steam reforming of methane. It is important to be able to calculate the distribution of gas properties within the porous structure in order to predict the performance of each cell and to determine the amount of internal reforming that takes place. This paper describes a three-dimensional numerical calculation method which has been developed to solve the governing equations in the porous structure. The calculation method includes the interaction between the flow in the porous medium and that in the adjacent fuel supply channel. The results highlight the importance of the kinetics of the reforming reaction and the thermal boundary conditions, both of which have a significant effect on the flow field within the porous structure. (Author)

  16. Heterogeneous atmospheric chemistry

    Science.gov (United States)

    Schryer, D. R.

    1982-01-01

    The present conference on heterogeneous atmospheric chemistry considers such topics concerning clusters, particles and microparticles as common problems in nucleation and growth, chemical kinetics, and catalysis, chemical reactions with aerosols, electron beam studies of natural and anthropogenic microparticles, and structural studies employing molecular beam techniques, as well as such gas-solid interaction topics as photoassisted reactions, catalyzed photolysis, and heterogeneous catalysis. Also discussed are sulfur dioxide absorption, oxidation, and oxidation inhibition in falling drops, sulfur dioxide/water equilibria, the evidence for heterogeneous catalysis in the atmosphere, the importance of heterogeneous processes to tropospheric chemistry, soot-catalyzed atmospheric reactions, and the concentrations and mechanisms of formation of sulfate in the atmospheric boundary layer.

  17. Development of Nested, Heterogeneous Ground-Water Flow Models for Study of Transport and Fate of Agricultural Chemicals, Merced County, California

    Science.gov (United States)

    Phillips, S. P.; Green, C. T.; Zamora, C.

    2006-05-01

    Multi-scale models of ground-water flow were developed as part of a study of the transport and fate of agricultural chemicals by the National Water-Quality Assessment (NAWQA) Program of the US Geological Survey. Agricultural chemicals of interest included forms of nitrogen and selected pesticides A three- dimensional local-scale model (17 square km) surrounds a well-instrumented, 1-km transect near the Merced River within a principally agricultural land-use setting. This model is nested within a regional-scale model (2,700 square km) of northeastern San Joaquin Valley, California, which provides hydrologically reasonable boundary conditions for the local model. Boundary fluxes were passed from the regional to local model using a hydraulic-conductivity-weighted distribution. The heterogeneity of aquifer materials was incorporated explicitly into the regional and local models. Three-dimensional kriging was used to interpolate sediment texture data from about 3,500 drillers' logs in the regional model area. The resulting distribution of sediment texture was used to estimate hydraulic parameters for each cell in the 16-layer regional model. A subset of these data was used to generate multiple transition-probability-based realizations of hydrofacies distributions for the 110-layer local model. Explicit depiction of heterogeneity in hydraulic conductivity and porosity in the local model incorporates macro-scale hydrodynamic dispersion into the flow model, allowing more direct comparison of particle-tracking results to tracer-derived estimates of ground-water age. Water levels measured in multi-depth wells along the 1-km transect were used to calibrate the local model (median error 0.12 m). Two-dimensional heat-flow models calibrated using continuous multi-depth temperature data from below the bed of the Merced River suggest an annual range of ground-water inflow of about 0-2.4 cm/d for water year 2005. This estimate compares reasonably well to the 4 cm/d simulated in the

  18. The spatial distribution and chemical heterogeneity of clinoptilolite at Yucca Mountain, Nye County, Nevada: Evidence for polygenetic hypogene alteration

    International Nuclear Information System (INIS)

    This part of TRAC's Annual Report for 1993 summarizes the finding of previous reports on the major element geochemistry of zeolitic alteration of the tuffs at Yucca Mountain and updates the status of work. In this report we examine the spatial distribution of zeolites by stratigraphic units and boreholes and the various types of chemical alteration of clinoptilolite indicated by the data reported in Broxton et al. and Bish and Chipera. The purpose is to evaluate the extent of the metasomatic alteration and to test the hypogene hypothesis of Szymanski. In this regard, it is of prime importance to evaluate whether the metasomatic alteration at Yucca Mountain is due to supergene or hypogene processes. In this report, the term open-quotes supergeneclose quotes denotes alteration and mineralization produced by fluids derived directly from atmospheric precipitation and infiltration through the vadose zone, and the term open-quotes hypogeneclose quotes denotes alteration and mineralization produced by fluids from the phreatic zone regardless of their former location or residence time in the Earth's crust. This report begins with a review of previous work on the genesis of zeolites of the Nevada Test Site

  19. Modeling Coupled Thermal-Hydrological-Chemical Processes in the Unsaturated Fractured Rock of Yucca Mountain, Nevada: Heterogeneity and Seepage

    International Nuclear Information System (INIS)

    An understanding of processes affecting seepage into emplacement tunnels is needed for correctly predicting the performance of underground radioactive waste repositories. It has been previously estimated that the capillary and vaporization barriers in the unsaturated fractured rock of Yucca Mountain are enough to prevent seepage under present day infiltration conditions. It has also been thought that a substantially elevated infiltration flux will be required to cause seepage after the thermal period is over. While coupled thermal-hydrological-chemical (THC) changes in Yucca Mountain host rock due to repository heating has been previously investigated, those THC models did not incorporate elements of the seepage model. In this paper, we combine the THC processes in unsaturated fractured rock with the processes affecting seepage. We observe that the THC processes alter the hydrological properties of the fractured rock through mineral precipitation and dissolution. We show that such alteration in the hydrological properties of the rock often leads to local flow channeling. We conclude that such local flow channeling may result in seepage under certain conditions, even with nonelevated infiltration fluxes

  20. The spatial distribution and chemical heterogeneity of clinoptilolite at Yucca Mountain, Nye County, Nevada: Evidence for polygenetic hypogene alteration

    Energy Technology Data Exchange (ETDEWEB)

    Livingston, D.E.; Szymanski, J.S.

    1994-01-01

    This part of TRAC`s Annual Report for 1993 summarizes the finding of previous reports on the major element geochemistry of zeolitic alteration of the tuffs at Yucca Mountain and updates the status of work. In this report we examine the spatial distribution of zeolites by stratigraphic units and boreholes and the various types of chemical alteration of clinoptilolite indicated by the data reported in Broxton et al. and Bish and Chipera. The purpose is to evaluate the extent of the metasomatic alteration and to test the hypogene hypothesis of Szymanski. In this regard, it is of prime importance to evaluate whether the metasomatic alteration at Yucca Mountain is due to supergene or hypogene processes. In this report, the term {open_quotes}supergene{close_quotes} denotes alteration and mineralization produced by fluids derived directly from atmospheric precipitation and infiltration through the vadose zone, and the term {open_quotes}hypogene{close_quotes} denotes alteration and mineralization produced by fluids from the phreatic zone regardless of their former location or residence time in the Earth`s crust. This report begins with a review of previous work on the genesis of zeolites of the Nevada Test Site.

  1. Fluid flow and heat transfer in rotating porous media

    CERN Document Server

    Vadasz, Peter

    2016-01-01

    This Book concentrates the available knowledge on rotating fluid flow and heat transfer in porous media in one single reference. Dr. Vadasz develops the fundamental theory of rotating flow and heat transfer in porous media and introduces systematic classification and identification of the relevant problems. An initial distinction between rotating flows in isothermal heterogeneous porous systems and natural convection in homogeneous non-­‐isothermal porous systems provides the two major classes of problems to be considered. A few examples of solutions to selected problems are presented, highlighting the significant impact of rotation on the flow in porous media.

  2. Porous Hydrogels

    Czech Academy of Sciences Publication Activity Database

    Přádný, Martin; Michálek, Jiří; Širc, Jakub

    New York: Nova Science Publishers, 2009 - (Acosta, J.; Camacho, A.), s. 57-74 ISBN 978-1-60741-401-8 R&D Projects: GA AV ČR 1QS400500558; GA MŠk 1M0538 Institutional research plan: CEZ:AV0Z40500505 Keywords : hydrogels * porous * tissue engineering Subject RIV: CD - Macromolecular Chemistry

  3. Modelling of the solidification process and the chemical heterogeneity of a 26NiCrMoV115 steel ingot: Modeliranje procesa strjevanja in kemične heterogenosti ingota iz jekla 26NiCrMoV115:

    OpenAIRE

    Balcar, Martin; Bažan, Jiří; Fila, Pavel; Martínek, Ludvík; Železný, Rudolf

    2007-01-01

    Steel making at ŽĎAS, a.s. using secondary metallurgy technology makes it possible to produce liquid metal with high levels of metallurgical cleanliness. During the casting and subsequent cooling of forging ingots, the steel solidification takes place. Directional material solidification, grain size, chemical heterogeneity and discontinuities can have a negative effect on the products' final properties. The comparison of the chemical composition based on a numerical calculation with the heter...

  4. Determination of chemical oxygen demand in heterogeneous solid or semisolid samples using a novel method combining solid dilutions as a preparation step followed by optimized closed reflux and colorimetric measurement

    OpenAIRE

    Noguerol Arias, Joan; Rodríguez-Abalde, Ángela; Romero, Eva; Flotats Ripoll, Xavier

    2012-01-01

    This paper reports the development of an innovative sample preparation method for the determination of the chemical oxygen demand (COD) in heterogeneous solid or semisolid samples, with high suspended solids and COD concentrations, using an optimized closed re flux colorimetric method.

  5. MRI of Heterogeneous Hydrogenation Reactions Using Parahydrogen Polarization

    Energy Technology Data Exchange (ETDEWEB)

    Burt, Scott Russell [Univ. of California, Berkeley, CA (United States)

    2008-01-01

    The power of magnetic resonance imaging (MRI) is its ability to image the internal structure of optically opaque samples and provide detailed maps of a variety of important parameters, such as density, diffusion, velocity and temperature. However, one of the fundamental limitations of this technique is its inherent low sensitivity. For example, the low signal to noise ratio (SNR) is particularly problematic for imaging gases in porous materials due to the low density of the gas and the large volume occluded by the porous material. This is unfortunate, as many industrially relevant chemical reactions take place at gas-surface interfaces in porous media, such as packed catalyst beds. Because of this severe SNR problem, many techniques have been developed to directly increase the signal strength. These techniques work by manipulating the nuclear spin populations to produce polarized} (i.e., non-equilibrium) states with resulting signal strengths that are orders of magnitude larger than those available at thermal equilibrium. This dissertation is concerned with an extension of a polarization technique based on the properties of parahydrogen. Specifically, I report on the novel use of heterogeneous catalysis to produce parahydrogen induced polarization and applications of this new technique to gas phase MRI and the characterization of micro-reactors. First, I provide an overview of nuclear magnetic resonance (NMR) and how parahydrogen is used to improve the SNR of the NMR signal. I then present experimental results demonstrating that it is possible to use heterogeneous catalysis to produce parahydrogen-induced polarization. These results are extended to imaging void spaces using a parahydrogen polarized gas. In the second half of this dissertation, I demonstrate the use of parahydrogen-polarized gas-phase MRI for characterizing catalytic microreactors. Specifically, I show how the improved SNR allows one to map parameters important for characterizing the heat and mass

  6. Porous substrates filled with nanomaterials

    Science.gov (United States)

    Worsley, Marcus A.; Baumann, Theodore F.; Satcher, Jr., Joe H.; Stadermann, Michael

    2014-08-19

    A composition comprising: at least one porous carbon monolith, such as a carbon aerogel, comprising internal pores, and at least one nanomaterial, such as carbon nanotubes, disposed uniformly throughout the internal pores. The nanomaterial can be disposed in the middle of the monolith. In addition, a method for making a monolithic solid with both high surface area and good bulk electrical conductivity is provided. A porous substrate having a thickness of 100 microns or more and comprising macropores throughout its thickness is prepared. At least one catalyst is deposited inside the porous substrate. Subsequently, chemical vapor deposition is used to uniformly deposit a nanomaterial in the macropores throughout the thickness of the porous substrate. Applications include electrical energy storage, such as batteries and capacitors, and hydrogen storage.

  7. Vibrational modes of porous silicon

    International Nuclear Information System (INIS)

    On the basis of theoretical and experimental investigations, the origin of room temperature photoluminescence (PL) from porous silicon is found to related to chemical complexes constituted the surface, in particular, SiHx, SiOx and SiOH groups. Ab initio atomic and molecular electronic structure calculations on select siloxane compounds were used for imitation of infrared (IR) spectra of porous silicon. These are compared to the IR spectra of porous silicon recorded by using Fourier Transform Infrared Spectroscopy (FTIR). In contrast to linear siloxane, the suggested circular siloxane terminated with linear siloxane structure is found to well-imitate the experimental spectra. These results are augmented with EDX (energy dispersive x-ray spectroscopy) measurements, which showed that the increase of SiOx content in porous silicon due to rapid oxidation process results in considerable decrease in PL peak intensity and a blue shift in the peak position. (author)

  8. Tritium transport in lithium ceramics porous media

    Energy Technology Data Exchange (ETDEWEB)

    Tam, S.W.; Ambrose, V.

    1991-12-31

    A random network model has been utilized to analyze the problem of tritium percolation through porous Li ceramic breeders. Local transport in each pore channel is described by a set of convection-diffusion-reaction equations. Long range transport is described by a matrix technique. The heterogeneous structure of the porous medium is accounted for via Monte Carlo methods. The model was then applied to an analysis of the relative contribution of diffusion and convective flow to tritium transport in porous lithium ceramics. 15 refs., 4 figs.

  9. Tritium transport in lithium ceramics porous media

    Energy Technology Data Exchange (ETDEWEB)

    Tam, S.W.; Ambrose, V.

    1991-01-01

    A random network model has been utilized to analyze the problem of tritium percolation through porous Li ceramic breeders. Local transport in each pore channel is described by a set of convection-diffusion-reaction equations. Long range transport is described by a matrix technique. The heterogeneous structure of the porous medium is accounted for via Monte Carlo methods. The model was then applied to an analysis of the relative contribution of diffusion and convective flow to tritium transport in porous lithium ceramics. 15 refs., 4 figs.

  10. Tritium transport in lithium ceramics porous media

    International Nuclear Information System (INIS)

    A random network model has been utilized to analyze the problem of tritium percolation through porous Li ceramic breeders. Local transport in each pore channel is described by a set of convection-diffusion-reaction equations. Long range transport is described by a matrix technique. The heterogeneous structure of the porous medium is accounted for via Monte Carlo methods. The model was then applied to an analysis of the relative contribution of diffusion and convective flow to tritium transport in porous lithium ceramics. 15 refs., 4 figs

  11. Simulation of Tracer Transport in Porous Media: Application to Bentonites

    International Nuclear Information System (INIS)

    We present a formal framework to describe tracer transport in heterogeneous media, such as porous media like bentonites. In these media, mean field approximation is not valid because there exist some geometrical constraints and the transport is anomalous. (Author)

  12. Multiphase multicomponent nonisothermal reactive transport in partially saturated porous media

    International Nuclear Information System (INIS)

    A numerical model MULTIFLO is developed for describing reactive transport in a multiphase-multicomponent, nonisothermal, partially saturated porous medium. The model includes chemical reactions between aqueous, gaseous and solid phases. Reactions involving minerals are considered to be irreversible and described through appropriate kinetic rate laws. Homogeneous reactions within the aqueous phase and heterogeneous reactions between aqueous and gaseous phases are assumed to be reversible, their reaction rates controlled by transport and local equilibrium mass action relations. Flow of aqueous and gaseous phases is described by Darcy's law in a partially saturated porous medium. Solute transport includes contributions from advection, diffusion and dispersion. Enhanced binary diffusion of water vapor for transport in a two-phase system is taken into account. A sequential solution algorithm is used to couple transport of water, air and heat to solute and minor gas components, and solids. Changes in porosity and permeability caused by chemical reactions are coupled to the flow field. Several options are available for solving numerically the solute and gaseous transport equations including fully implicit, explicit and operator splitting methods. Mineral mass transfer equations are solved using an explicit finite difference scheme. The coupled flow and transport model is applied to the proposed high-level nuclear waste storage facility located in unsaturated rock at Yucca Mountain, Nevada. A repository-scale model is used to calculate the redistribution of moisture, heat, and various chemical constituents caused by the thermal perturbation produced by the waste. (author)

  13. Mixed convective MHD flow of a micropolar fluid with ohmic heating, radiation and viscous dissipation over a chemically reacting porous plate subjected to a constant heat flux and concentration gradient

    Directory of Open Access Journals (Sweden)

    Kumar Hitesh

    2014-01-01

    Full Text Available In the present paper analysis of a chemically reacting mixed convection MHD micropolar flow, heat and mass transfer in porous medium with the effects of ohmic heating, radiation and viscous dissipation past an infinite vertical plate which is subjected to a constant heat flux and the concentration gradient. The non-linear coupled partial differential equations are solved numerically using an implicit finite difference scheme known as Keller-box method. The results for concentration, transverse velocity, angular velocity and temperature are obtained and illustrated graphically to observe the effects of various parameters, and the numerical discussion is presented with physical interpretations.

  14. Multiphase, Multicomponent Fluid Flow in Homogeneous and Heterogeneous Porous Media Écoulement de fluides multiconstituants polyphasiques dans des milieux poreux homogènes et hétérogènes

    Directory of Open Access Journals (Sweden)

    Chella R.

    2006-12-01

    Full Text Available The flow of several components and several phases through a porous medium is generally described by introducing macroscopic mass-balance equations under the form of generalized dispersion equations. This model raises several questions that are discussed in this paper on the basis of results obtained from the volume averaging method, coupled with pore-scale simulations of the multiphase flow. The study is limited to a binary, two-phase system, and we assume that the momentum equations can be solved independently from the diffusion/advection equations. The assumption of local-equilibrium is discussed and several length-scale and time-scale constraints are provided. A key issue concerns the impact on the dispersion tensors of the pore-scale equilibrium condition at the interface between the different phases. Our results show that this phenomenon may lead to significant variations of the dispersion coefficients with respect to passive dispersion, i. e. , dispersion without interfacial mass fluxes. Macroscopic equations are then obtained in the general case, and several local closure problems are provided that allow one to calculate the dispersion tensors and others properties, from the pore-scale geometry, velocities, and fluid characteristics. Examples of solutions of these closure problems are given in the case of two-dimensional representative unit cells. The two-phase flow equations are solved in two different ways : a boundary element technique, or a modified lattice Boltzmann approach. Solutions of the closure problems associated with the dispersion equations are then given using a finite volume element formulation of the partial differential equations. The results show the influence of velocity and saturation on the effective parameters. They emphasize the importance of geometry on the behavior of the dispersion tensor. Extension of these results to a larger-scale including the effect of heterogeneities is proposed in a limited case

  15. Chemical stability of 99mTc–DTPA under aerobic and microbially mediated Fe(III)-reducing conditions in porous media

    International Nuclear Information System (INIS)

    99mTc–DTPA has been used as a conservative tracer to quantify water transport through porous media. However, more information on the reactivity of this 99mTc compound under varying geochemical conditions is desirable to better understand its potential uses. We measured the speciation of Tc following amendment of 99mTc–DTPA to batch systems spanning a range of controlled biogeochemical conditions. Our results suggest that 99mTc–DTPA is stable under the reducing conditions tested. However, freshly precipitated Al–ferrihydrite may displace Tc(IV) from DTPA in the absence of Fe(III)-reducing conditions. - Highlights: • 99mTc–DTPA has been used to quantify water transport through porous media • 99mTc–DTPA does not always behave conservatively • Iron mineral surfaces can sometimes competitively bind DTPA • Reactivity of 99mTc–DTPA should be evaluated according to factors discussed

  16. Effect of Thermo-Diffusion and Chemical Reaction on Mixed Convective Heat And Mass Transfer Through A Porous Medium In Cylindrical Annulus With Heat Source.

    Directory of Open Access Journals (Sweden)

    Dr.K.Gnaneswar

    2014-09-01

    Full Text Available A finite element study of combined heat and mass transfer flow through a porous medium in a circular cylindrical annulus with Soret and Dufour effects in the presence of heat sources has been analyzed. The coupled velocity, energy, and diffusion equations are solved numerically by using Galerkin- finite element technique. Shear stress, Nusslet number and Sherwood number are evaluated numerically for different values of the governing parameters under consideration and are shown in tabular form.

  17. Effect of Thermo-Diffusion and Chemical Reaction on Mixed Convective Heat And Mass Transfer Through A Porous Medium In Cylindrical Annulus With Heat Source.

    OpenAIRE

    Dr.K.Gnaneswar

    2014-01-01

    A finite element study of combined heat and mass transfer flow through a porous medium in a circular cylindrical annulus with Soret and Dufour effects in the presence of heat sources has been analyzed. The coupled velocity, energy, and diffusion equations are solved numerically by using Galerkin- finite element technique. Shear stress, Nusslet number and Sherwood number are evaluated numerically for different values of the governing parameters under consideration and are shown...

  18. Influence of permeability anisotropy on mixing controlled reactive transport simulations in porous media

    Science.gov (United States)

    Chiogna, Gabriele; Herrera, Paulo

    2015-04-01

    Several studies have demonstrated how plume deformation induced by flow heterogeneity in porous media can enhance mixing of reactants. This enhancement can have important impact on mixing controlled reactions such a biodegradation of plumes of organic compounds. On the other hand, recent studies have indicated the possibility of observing complex flow topology on groundwater flow that occurs in anisotropic yet homogenous porous media. Moreover, it has been demonstrated that those complex flow topologies can also enhance solute mixing. We study the effect of medium anisotropy on reactive solute transport for the case of a chemical reactor composed of two homogeneous anisotropic layers. We simulate different injection strategies for different chemical reactions that involve two reactants. We demonstrate the effect of the medium anisotropy by analyzing the results of the simulations and identify best strategies for the operation and design of the system to maximize reaction rates. These findings could have potential application in the design of new remediation systems for contaminated groundwater, chemical reactors and other engineering problems that involve flow through porous media.

  19. Heterogeneous Catalysis.

    Science.gov (United States)

    Miranda, R.

    1989-01-01

    Described is a heterogeneous catalysis course which has elements of materials processing embedded in the classical format of catalytic mechanisms and surface chemistry. A course outline and list of examples of recent review papers written by students are provided. (MVL)

  20. Methane Activation by Heterogeneous Catalysis

    OpenAIRE

    Horn, R.; Schlögl, R.

    2015-01-01

    Methane activation by heterogeneous catalysis will play a key role to secure the supply of energy, chemicals and fuels in the future. Methane is the main constituent of natural gas and biogas and it is also found in crystalline hydrates at the continental slopes of many oceans and in permafrost areas. In view of this vast reserves and resources, the use of methane as chemical feedstock has to be intensified. The present review presents recent results and developments in heterogeneous catalyti...

  1. Chemical modulation on heterogeneous growth in Prochilodus lineatus (Valenciennes, 1847) (Pisces; Characiformes) Modulação química sobre o crescimento heterogêneo em Prochilodus lineatus (Valenciennes, 1847) (Pisces; Characiformes)

    OpenAIRE

    JM. Barbosa; GL. Volpato

    2007-01-01

    In the present study, the effect of chemical factors released by conspecifics on growth variability (heterogeneous growth - HetG) in a gregarious fish species (Prochilodus lineatus) was tested. HetG was assessed by the weight variation coefficient in two consecutive 21-day periods. The fish were grouped in tanks (4 fish in each) that received running water with constant draining. The tanks contained either conspecifics (C) or non-conspecifics (N). Four conditions were established in accordanc...

  2. Modification of chemical and physical factors in steamflood to increase heavy oil recovery

    Energy Technology Data Exchange (ETDEWEB)

    Yortsos, Y.C.

    1990-02-01

    This report summarizes research progress made during the period October 1, 1988--September 30, 1989. We report advances in the following general areas: (1) chemical-steam simulation model, (2) vapor-liquid flow in porous media, (3) foam flow in porous media, (4) caustic flooding at elevated temperatures, and (5) reservoir heterogeneity. Additional efforts have been devoted in the last quarter of the past year in upgrading and debugging the simulator. New features were added in three-phase relative permeabilities, the vertical equilibrium and the phase behavior subroutines. 123 refs., 79 figs., 2 tabs.

  3. A computer model for one-dimensional mass and energy transport in and around chemically reacting particles, including complex gas-phase chemistry, multicomponent molecular diffusion, surface evaporation, and heterogeneous reaction

    Science.gov (United States)

    Cho, S. Y.; Yetter, R. A.; Dryer, F. L.

    1992-01-01

    Various chemically reacting flow problems highlighting chemical and physical fundamentals rather than flow geometry are presently investigated by means of a comprehensive mathematical model that incorporates multicomponent molecular diffusion, complex chemistry, and heterogeneous processes, in the interest of obtaining sensitivity-related information. The sensitivity equations were decoupled from those of the model, and then integrated one time-step behind the integration of the model equations, and analytical Jacobian matrices were applied to improve the accuracy of sensitivity coefficients that are calculated together with model solutions.

  4. Heterogeneous catalysis fundamentals and applications

    CERN Document Server

    Ross, Julian RH

    2011-01-01

    Heterogeneous catalysis plays a part in the production of more than 80% of all chemical products. It is therefore essential that all chemists and chemical engineers have an understanding of the fundamental principles as well as the applications of heterogeneous catalysts. This book introduces the subject, starting at a basic level, and includes sections on adsorption and surface science, catalytic kinetics, experimental methods for preparing and studying heterogeneous catalysts, as well as some aspects of the design of industrial catalytic reactors. It ends with a chapter that covers a range

  5. Porous Ascend

    DEFF Research Database (Denmark)

    Riiber, Jacob; Tamke, Martin; Ramsgaard Thomsen, Mette

    2012-01-01

    towards a novel approach to working with, and reproducing, complexity within collections of architectural components. With no predefined coordinization mapping the ever changing fractal pattern, building proceeds by a locally defined identification and pairing of elements. In this way the project......The Porous Ascend project investigates how algorithmic and generative approaches allows for the utilization of complex, and by other means inaccessible, ways of devising the schema by which we arrange the parts of an architectural object. It does so by pursuing to physically realize a structure of...... folded elements, based on the concept of applying recursion to the geometry of the non-periodic Penrose tiling. Within this process the project explores questions regarding the making of bespoke digital design tools, digital production, material behaviour and assemblage strategies. The project points...

  6. CHEMICALS

    CERN Multimedia

    Medical Service

    2002-01-01

    It is reminded that all persons who use chemicals must inform CERN's Chemistry Service (TIS-GS-GC) and the CERN Medical Service (TIS-ME). Information concerning their toxicity or other hazards as well as the necessary individual and collective protection measures will be provided by these two services. Users must be in possession of a material safety data sheet (MSDS) for each chemical used. These can be obtained by one of several means : the manufacturer of the chemical (legally obliged to supply an MSDS for each chemical delivered) ; CERN's Chemistry Service of the General Safety Group of TIS ; for chemicals and gases available in the CERN Stores the MSDS has been made available via EDH either in pdf format or else via a link to the supplier's web site. Training courses in chemical safety are available for registration via HR-TD. CERN Medical Service : TIS-ME :73186 or service.medical@cern.ch Chemistry Service : TIS-GS-GC : 78546

  7. Heterogeneous reactors

    International Nuclear Information System (INIS)

    The microscopic study of a cell is meant for the determination of the infinite multiplication factor of the cell, which is given by the four factor formula: K(infinite) = n(epsilon)pf. The analysis of an homogeneous reactor is similar to that of an heterogeneous reactor, but each factor of the four factor formula can not be calculated by the formulas developed in the case of an homogeneous reactor. A great number of methods was developed for the calculation of heterogeneous reactors and some of them are discussed. (Author)

  8. Heterogeneous chromium catalysts

    OpenAIRE

    2005-01-01

    The present invention relates to a heterogeneous chromium catalyst system for the polymerisation of ethylene and/or alpha olefins prepared by the steps of: (a) providing a silica-containing support, (b) treating the silica-containing support with a chromium compound to form a chromium-based silica-containing support, (c) activating the chromium-based silica-containing support, (d) chemically reducing the activated chromium-based silica-containing support to produce a precursor catalyst, (e) r...

  9. Modeling of Mineral Precipitation and Dissolution for Various Reactant Mixing Patterns in Porous Media

    Science.gov (United States)

    Guo, L.; Huang, H.; Redden, G. D.; Fox, D. T.; Hu, B. X.

    2008-12-01

    Spatial and temporal distribution of mineral precipitates in porous media depends on how amendments are delivered and mineral-forming substrates are mixed. The spatial and temporal distribution of precipitation products are determined mainly by the injection geometry, the sequence of reactant injection, and physical and chemical heterogeneity of the system. In this study, two scenarios for mixing Ca2+ and bicarbonate in porous media are simulated using TOUGHREACT: parallel injection and sequential injection. For parallel flow injection scenario in which solutions containing mineral-forming solutes are injected side-by-side, a relatively wide mixing zone is formed. However, a much narrower precipitation zone is observed to evolve in the simulation, which is consistent with laboratory flow cell experiments. When the feedback effects between changes in porosity and permeability and mineral precipitation are not considered, the precipitation zone propagates towards the bicarbonate solution due to chemical asymmetry with respect to proton activities on both sides of the precipitation zone. Sensitivity studies of precipitation to diffusion coefficient, reaction network, kinetic reaction rate formula, and reaction rate constant are conducted to investigate controlling mechanisms and parameters mostly relevant to experiment conditions. In sequential injection scenario in which solutions containing Ca2+ and bicarbonate are injected one after the other, a migrating mixing and precipitation zone is formed and travels through the simulated porous medium, which is consistent with our laboratory flow cell experiments.

  10. Superhydrophobicity on nanostructured porous hydrophilic material

    Science.gov (United States)

    Jiang, Hong-Ren; Chan, Deng-Chi

    2016-04-01

    By applying laser oxidation, ablation, and plasma treatment to modify a surface of polydimethylsiloxane, we show that creating hydrophobic sites on an originally superhydrophilic nanostructured porous surface greatly changes the wetting properties of the surface. The modified surface may even become superhydrophobic while the ratio of added hydrophobic site to the surface is relatively low. The relation between the contact angles and the effect of hydrophobic sites is further tested in blade scraping method and a similar result is also obtained. This method to achieve superhydrophobicity on the hydrophilic nanostructured porous material may open possibilities for achieving superhydrophobicity and enable functional superhydrophobic surfaces with heterogeneous components.

  11. MHD Flow Heat and Mass Transfer of Micropolar Fluid over a Nonlinear Stretching Sheet with Variable Micro Inertia Density, Heat Flux and Chemical Reaction in a Non-darcy Porous Medium

    Directory of Open Access Journals (Sweden)

    . Dr. S. Rawat

    2016-01-01

    Full Text Available This paper investigates the two dimensional flow, heat and mass transfer of chemically reacting Micropolar fluid over a non-linear stretching sheet with variable heat flux in a non-darcy porous medium. The rate of chemical reaction is assumed to be constant throughout the fluid i.e. homogenous. Using a similarity transformation, the governing partial differential equations are transformed into a system of ordinary differential equation, which is then solved using Finite element method. Numerical results regarding local Nussult No. are shown graphically with Magnetic number (ܰ݉௫ for variation in heat transfer exponent (n. This study also analyzes the effect of velocity exponent m, heat transfer exponent n, material parameter K, Magnetic Number(ܰ݉௫Darcy NumberDax, Forchheimer Number Nfx, Prandtl number Pr, Schmidt Number Sc and Chemical reaction rate parameter x on velocity, microrotation, temperature and concentration profiles. Velocity exponent m has a positive effect on the velocity, temperature and concentration profiles while microrotation decreases as m increases. Graphical results shows that the thermal boundary layer thickness decreases at and near the wall with the increase in heat flux exponent n. Also an increase in K leads to a decrease in skin friction parameter as well as the wall couple stress.

  12. Measuring Heterogeneous Reaction Rates with ATR-FTIR Spectroscopy to Evaluate Chemical Fates in an Atmospheric Environment: A Physical Chemistry and Environmental Chemistry Laboratory Experiment

    Science.gov (United States)

    Roberts, Jason E.; Zeng, Guang; Maron, Marta K.; Mach, Mindy; Dwebi, Iman; Liu, Yong

    2016-01-01

    This paper reports an undergraduate laboratory experiment to measure heterogeneous liquid/gas reaction kinetics (ozone-oleic acid and ozone-phenothrin) using a flow reactor coupled to an attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectrometer. The experiment is specially designed for an upper-level undergraduate Physical…

  13. Mesoscale poroelasticity of heterogeneous media

    Science.gov (United States)

    Monfared, Siavash; Laubie, Hadrien; Radjai, Farhang; Pellenq, Roland; Ulm, Franz-Josef

    Poroelastic behavior of heterogeneous media is revisited. Lattice Element Method (LEM) is used to model interaction between solid constituents due to a pressurized pore space. Exploring beyond mean-field based theories in continuum microporomechanics, local textural variations and its contribution to the global anisotropic poroelastic behavior of real multiphase porous media are captured. To this end, statistical distributions of mesoscale poroelastic coefficients from numerical simulations on X-ray microscopy scans of two different organic-rich shales with different microtextures are presented. The results are compared with predictions using mean-field based tools of continuum micromechanics. The textural dependency of strain localization and stress chain formation captured in this framework promises a powerful tool for modeling poroelastic response of complex porous composites and a path to incorporate local textural and elastic variations into a continuum description. Visiting Scientist, CNRS-MIT, MIT.

  14. 多孔阳极氧化铝的化学修饰及其应用于过氧化氢的测定%Chemical Modification of Porous Anodic Alumina and Application in Detection of Hydrogen Peroxide

    Institute of Scientific and Technical Information of China (English)

    徐国荣; 唐安平

    2011-01-01

    A new hydrogen peroxide electrochemical biosensor was fabricated through adsorbed cytochrome C in porous anodic alumina chemically modified. The barrier layer at the bottom of the porous anodic alumina was erased by chemical and electrochemical erosion. The Au nano particles were deposited in porous anodic alumina by two-step electroless deposition, and then the cytochrome C was immobilization on Nano Au bed in solution including L-cyste-ine through self-assembled technology. Then a new hydrogen peroxide biosensor was fabricated. The electrochemical and electro catalytic behavior of the cytochrome C electrode was characterized by cyclic voltammetry and chrono-amperometry. The cytochrome C electrode showed a pair of stable and well-defined peaks at about -50 mV and -190 mV at 80 mV/s in pH 7.0 PBS and displayed excellent electro catalytic responses to the reduction of hydrogen peroxide with linear relationship over a concentration range from 1.5xl0-5 mol/L to 4. 8xl0-4 mol/L,and a detection limit of 3.5 x10-6 mol/L( S/N = 3). The results of this study reveal porous anodic alumina chemically modified could be used for the design of biosensors with good operational lifetimes.%多孔阳极氧化铝经化学修饰后吸附细胞色素C,制备了过氧化氢生物传感器电极。多孔阳极氧化铝通过电化学和化学腐蚀阻挡层后,用两步无电沉积方法制备了纳米金修饰的多孔阳极氧化铝电极,再在含有L-半胱氨酸的细胞色素C的溶液中通过吸附制备细胞色素C电极。用循环伏安法和计时电流法测试细胞色素C电极的电化学性能及催化对过氧化氢的还原。结果表明,包覆的细胞色素C电极显示较好的稳定性,在扫描速度为80 mV/s时于-50 mV、-190mV附近出现一对稳定的氧化还原峰。该电极对过氧化氢具有良好的电催化还原性能,在1.5×10-5mol/L~4.8×10-4 mol/L浓度范围内,电流与浓度呈良好的线性关系。多孔阳极氧化铝

  15. Convection in porous media

    CERN Document Server

    Nield, Donald A

    1992-01-01

    This book provides a user-friendly introduction to the topic of convection in porous media The authors as- sume that the reader is familiar with the basic elements of fluid mechanics and heat transfer, but otherwise the book is self-contained The book will be useful both as a review (for reference) and as a tutorial work, suitable as a textbook in a graduate course or seminar The book brings into perspective the voluminous research that has been performed during the last two decades The field has recently exploded because of worldwide concern with issues such as energy self-sufficiency and pollution of the environment Areas of application include the insulation of buildings and equipment, energy storage and recovery, geothermal reservoirs, nuclear waste disposal, chemical reactor engineering, and the storage of heat-generating materials such as grain and coal Geophysical applications range from the flow of groundwater around hot intrusions to the stability of snow against avalanches

  16. Amine Functionalized Porous Network

    KAUST Repository

    Eddaoudi, Mohamed

    2015-05-28

    Amine groups can be introduced in porous materials by a direct (one pot) or post-synthetic modification (PSM) process on aldehyde groups, and the resulting porous materials have increased gas affinity.

  17. Chemical, thermal and mechanical stabilities of metal-organic frameworks

    Science.gov (United States)

    Howarth, Ashlee J.; Liu, Yangyang; Li, Peng; Li, Zhanyong; Wang, Timothy C.; Hupp, Joseph T.; Farha, Omar K.

    2016-03-01

    The construction of thousands of well-defined, porous, metal-organic framework (MOF) structures, spanning a broad range of topologies and an even broader range of pore sizes and chemical functionalities, has fuelled the exploration of many applications. Accompanying this applied focus has been a recognition of the need to engender MOFs with mechanical, thermal and/or chemical stability. Chemical stability in acidic, basic and neutral aqueous solutions is important. Advances over recent years have made it possible to design MOFs that possess different combinations of mechanical, thermal and chemical stability. Here, we review these advances and the associated design principles and synthesis strategies. We focus on how these advances may render MOFs effective as heterogeneous catalysts, both in chemically harsh condensed phases and in thermally challenging conditions relevant to gas-phase reactions. Finally, we briefly discuss future directions of study for the production of highly stable MOFs.

  18. Evaluation of the effects of microscale chemical and isotopic heterogeneity of coral skeleton on conventional Sr/Ca and O paleothermometers

    Science.gov (United States)

    Mitsuguchi, Takehiro

    2013-10-01

    Recent studies using secondary ion mass spectrometry revealed microscale heterogeneity of Sr/Ca and O in shallow-water coral skeletons, i.e., Sr/Ca and O differ significantly between two basic microfeatures of the skeleton: the center of calcification (COC) and surrounding fibrous skeleton (SFS). The COC, in contrast with the SFS, consists of highly irregular crystals intermingled with significant amount of organic matter; therefore, analyzing the SFS only would probably be favourable for paleotemperature reconstruction. Conventional Sr/Ca and O paleothermometers are, however, based on the analysis of the mixture of the COC and SFS, and thus may be significantly affected by the above-mentioned heterogeneity. In this study, I have evaluated the heterogeneity-induced effects on the conventional paleothermometers of Porites skeletons using published Sr/Ca, O and volume-fraction data of the COC and SFS and published observations of seasonal variability of bulk skeletal density. Results indicate that the effects may yield significant or serious errors in paleotemperature reconstruction.

  19. Evaluation of the effects of microscale chemical and isotopic heterogeneity of coral skeleton on conventional Sr/Ca and 18O paleothermometers

    Indian Academy of Sciences (India)

    Takehiro Mitsuguchi

    2013-10-01

    Recent studies using secondary ion mass spectrometry revealed microscale heterogeneity of Sr/Ca and 18O in shallow-water coral skeletons, i.e., Sr/Ca and 18O differ significantly between two basic microfeatures of the skeleton: the center of calcification (COC) and surrounding fibrous skeleton (SFS). The COC, in contrast with the SFS, consists of highly irregular crystals intermingled with significant amount of organic matter; therefore, analyzing the SFS only would probably be favourable for paleotemperature reconstruction. Conventional Sr/Ca and 18O paleothermometers are, however, based on the analysis of the mixture of the COC and SFS, and thus may be significantly affected by the above-mentioned heterogeneity. In this study, I have evaluated the heterogeneity-induced effects on the conventional paleothermometers of Porites skeletons using published Sr/Ca, 18O and volume-fraction data of the COC and SFS and published observations of seasonal variability of bulk skeletal density. Results indicate that the effects may yield significant or serious errors in paleotemperature reconstruction.

  20. Synthesis and characterization of a new material based on porous silica-Chemically immobilized C,N-pyridylpyrazole for heavy metals adsorption

    International Nuclear Information System (INIS)

    The immobilization of C,N-pyridylpyrazole on the surface of epoxy group containing silica gel phase for the formation of a newly synthesized material based on porous silica-bound C,N-pyridylpyrazole (SGPP) is described. The surface modification was characterized by 13C NMR of solid sample, elemental analysis and infrared spectra and was studied and evaluated by determination of the surface area using the BET equation, the adsorption and desorption capability using the isotherm of nitrogen and BJH pore sizes, respectively. The new material exhibits good thermal stability determined by thermogravimetry curves. The synthesized material was utilised in column and batch methods for separation and trace extraction of (Hg2+, Cd2+, Pb2+, Cu2+, Zn2+, K+, Na+ and Li+) and compared to results of classical liquid-liquid extraction with the unbound C,N-pyridylpyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the material exhibits a high selectivity toward Hg(II)

  1. Synthesis and characterization of a new material based on porous silica-Chemically immobilized C,N-pyridylpyrazole for heavy metals adsorption

    Energy Technology Data Exchange (ETDEWEB)

    Radi, Smaail [Laboratoire de Chimie Organique, Macromoleculaire et Produits Naturels, Departement de Chimie, Faculte des Sciences, Universite Mohamed 1er, BP 524, 60 000 Oujda (Morocco)], E-mail: radi_smaail@yahoo.fr; Attayibat, Ahmed [Laboratoire de Chimie Organique, Macromoleculaire et Produits Naturels, Departement de Chimie, Faculte des Sciences, Universite Mohamed 1er, BP 524, 60 000 Oujda (Morocco); Lekchiri, Yahya [Laboratoire de Biochimie, Departement de Biologie, Faculte des Sciences, Universite Mohamed 1er, BP 524, 60 000 Oujda (Morocco); Ramdani, Abdelkrim [Laboratoire de Chimie Organique, Macromoleculaire et Produits Naturels, Departement de Chimie, Faculte des Sciences, Universite Mohamed 1er, BP 524, 60 000 Oujda (Morocco); Bacquet, Maryse [Laboratoire de Chimie Macromoleculaire, Universite des Sciences et Technologies de Lille, 59655 Villeneuve d' Ascq (France)

    2008-10-15

    The immobilization of C,N-pyridylpyrazole on the surface of epoxy group containing silica gel phase for the formation of a newly synthesized material based on porous silica-bound C,N-pyridylpyrazole (SGPP) is described. The surface modification was characterized by {sup 13}C NMR of solid sample, elemental analysis and infrared spectra and was studied and evaluated by determination of the surface area using the BET equation, the adsorption and desorption capability using the isotherm of nitrogen and BJH pore sizes, respectively. The new material exhibits good thermal stability determined by thermogravimetry curves. The synthesized material was utilised in column and batch methods for separation and trace extraction of (Hg{sup 2+}, Cd{sup 2+}, Pb{sup 2+}, Cu{sup 2+}, Zn{sup 2+}, K{sup +}, Na{sup +} and Li{sup +}) and compared to results of classical liquid-liquid extraction with the unbound C,N-pyridylpyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the material exhibits a high selectivity toward Hg(II)

  2. Revisiting the Stӧber method: Design of nitrogen-doped porous carbon spheres from molecular precursors of different chemical structures.

    Science.gov (United States)

    Tian, Hao; Liu, Jian; O'Donnell, Kane; Liu, Tingting; Liu, Xinmei; Yan, Zifeng; Liu, Shaomin; Jaroniec, Mietek

    2016-08-15

    Porous polymer resins and carbon spheres have been successfully prepared by an extended Stӧber method using phenol derivatives of different functionality. Herein, the Stӧber method is revised and used for the preparation of phenolic resin spheres from a series of hetero-atoms containing phenol derivatives (such as nitrophenol, aminophenol and halide-substituted phenols), which upon carbonization are converted to heteroatom-doped carbon spheres. The use of 4-amino-3-nitrophenol affords monodispersed carbon spheres with unprecedentedly high nitrogen content of about 11.9wt%. In this synthesis phenolic resin is initially formed by polymerizing formaldehyde with one of the aforementioned phenol derivatives, which acts as a resin precursor and source of heteroatoms to be doped. When amino group in aminophenol is in meta position the monodisperse phenolic resin and subsequently converted-doped carbon spheres are obtained. The resultant carbon spheres were examined as potential CO2 adsorbents and electrode materials for supercapacitors, reaching CO2 uptake of 89cm(3) STP/g (at 273K and 1.0bar), and the electrochemical capacitance of 127 F/g under basic conditions, respectively. This study provides some guidelines for design of carbon spheres by selecting phenolic resin precursors with desired molecular structures and functionalities for specific applications. PMID:27208436

  3. Group theory transformation for Soret and Dufour effects on free convective heat and mass transfer with thermophoresis and chemical reaction over a porous stretching surface in the presence of heat source/sink

    Energy Technology Data Exchange (ETDEWEB)

    Kandasamy, R., E-mail: future990@gmail.com [Computational Fluid Dynamics, FSSW, Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johore (Malaysia); Hayat, T. [Department of Mathematics, Quaid-i-Azam University Islamabad (Pakistan); Department of Mathematics, College of Science, King Saud University, P.O. Box 2455, Riyadh 1451 (Saudi Arabia); Obaidat, S. [Department of Mathematics, College of Science, King Saud University, P.O. Box 2455, Riyadh 1451 (Saudi Arabia)

    2011-06-15

    Highlights: > The group theoretic method is of wide applicability. > Concentration boundary layer is significantly suppressed by the thermophoretic force. > Impact of Soret and Dufour effects in the presence of thermophoresis particle deposition with chemical reaction plays an important role on the flow field. - Abstract: The group theoretic method is applied for solving the problem of combined effect of thermal diffusion and diffusion thermo on free convective heat and mass transfer over a porous stretching surface in the presence of thermophoresis particle deposition with variable stream conditions. The application of one-parameter groups reduces the number of independent variables by one and consequently, the system of governing partial differential equations with the boundary conditions reduces to a system of ordinary differential equations with appropriate boundary conditions. The equations along with the boundary conditions are solved numerically by using Runge Kutta Gill integration scheme with shooting technique. Impact of Soret and Dufour effects in the presence of thermophoresis particle deposition with chemical reaction plays an important role on the flow field. The results thus obtained are presented graphically and discussed.

  4. Study of water radiolysis in porous media

    International Nuclear Information System (INIS)

    The understanding of the production of H2 in the radiolysis of water confined into pores of concrete is important for the disposal of radioactive waste. In order to describe the mechanisms of water radiolysis in such heterogeneous porous systems we have studied the behaviour under gamma radiation of water confined in porous silica glasses with pores going from 8 to 300 nm of diameter and meso-porous molecular sieves (MCM-41). The radiolytic yields of hydroxyl radicals, hydrated electron and dihydrogen, have been determined with respect to the pore size of materials. The increase of these radiolytic yields compared to those of free water allowed us to show a charge transfer from silica to confined water. On the other hand the kinetics of hydrated electron reactions measured by pulse radiolysis are not modified. (author)

  5. The code IVA 4: second law of thermodynamics for multi-phase multi-component flows in heterogeneous media

    International Nuclear Information System (INIS)

    Local volume and time averaging is used to derive rigorously energy equations for multi-phase flows in heterogeneous porous media. The flow is conditionally divided into three velocity fields. Each of the fields consists of several chemical components. Using the conservation equations for mass and momentum and the Gibbs equation, entropy equations are rigorously derived. It is shown that the use of the specific entropy as one of the dependent variables leads to the simplest way of describing and modeling such a complicated thermodynamic system. A working form of the final entropy equation is recommended for general use in multi-phase flow dynamics. (orig.)

  6. Chemical Heterogeneity of a Large Cluster IDP: Clues to its Formation History Using X-ray Fluorescence Mapping and XANES Spectroscopy

    Science.gov (United States)

    Wirick, S.; Flynn, G. J.; Sutton, S.; Zolensky, M. E.

    2013-01-01

    Chondritic porous IDPs may be among the most primitive objects found in our solar system [1]. They consist of many micron to submicron minerals, glasses and carbonaceous matter [2,3,4,5,6,7] with > 10(exp 4) grains in a 10 micron cluster [8]. Speculation on the environment where these fine grained, porous IDPs formed varies with possible sources being presolar dusty plasma clouds, protostellar condensation, solar asteroids or comets [4,6,9]. Also, fine grained dust forms in our solar system today [10,11]. Isotopic anomalies in some particles in IDPs suggest an interstellar source[4,7,12]. IDPs contain relic particles left from the dusty plasma that existed before the protostellar disk formed and other grains in the IDPs formed later after the cold dense nebula cloud collapsed to form our protostar and other grains formed more recently. Fe and CR XANES spectroscopy is used here to investigate the oxygen environment in a large (>50 10 micron or larger sub-units) IDP. Conclusions: Analyzing large (>50 10 micron or larger sub-units) CP IDPs gives one a view on the environments where these fine dust grains formed which is different from that found by only analyzing the small, 10 micron IDPs. As with cluster IDP L2008#5 [3], L2009R2 cluster #13 appears to be an aggregate of grains that sample a diversity of solar and perhaps presolar environments. Sub-micron, grain by grain measurement of trace element contents and elemental oxidation states determined by XANES spectroscopy offers the possibility of understanding the environments in which these grains formed when compared to standard spectra. By comparing thermodynamic modeling of condensates with analytical data an understanding of transport mechanisms operating in the early solar system may be attained.

  7. Photonic Crystal Sensors Based on Porous Silicon

    Directory of Open Access Journals (Sweden)

    Claudia Pacholski

    2013-04-01

    Full Text Available Porous silicon has been established as an excellent sensing platform for the optical detection of hazardous chemicals and biomolecular interactions such as DNA hybridization, antigen/antibody binding, and enzymatic reactions. Its porous nature provides a high surface area within a small volume, which can be easily controlled by changing the pore sizes. As the porosity and consequently the refractive index of an etched porous silicon layer depends on the electrochemial etching conditions photonic crystals composed of multilayered porous silicon films with well-resolved and narrow optical reflectivity features can easily be obtained. The prominent optical response of the photonic crystal decreases the detection limit and therefore increases the sensitivity of porous silicon sensors in comparison to sensors utilizing Fabry-Pérot based optical transduction. Development of porous silicon photonic crystal sensors which allow for the detection of analytes by the naked eye using a simple color change or the fabrication of stacked porous silicon photonic crystals showing two distinct optical features which can be utilized for the discrimination of analytes emphasize its high application potential.

  8. Heterogeneous Materials I and Heterogeneous Materials II

    International Nuclear Information System (INIS)

    In these two volumes the author provides a comprehensive survey of the various mathematically-based models used in the research literature to predict the mechanical, thermal and electrical properties of hetereogeneous materials, i.e., materials containing two or more phases such as fibre-reinforced polymers, cast iron and porous ceramic kiln furniture. Volume I covers linear properties such as linear dielectric constant, effective electrical conductivity and elastic moduli, while Volume II covers nonlinear properties, fracture and atomistic and multiscale modelling. Where appropriate, particular attention is paid to the use of fractal geometry and percolation theory in describing the structure and properties of these materials. The books are advanced level texts reflecting the research interests of the author which will be of significant interest to research scientists working at the forefront of the areas covered by the books. Others working more generally in the field of materials science interested in comparing predictions of properties with experimental results may well find the mathematical level quite daunting initially, as it is apparent that the author assumes a level of mathematics consistent with that taught in final year undergraduate and graduate theoretical physics courses. However, for such readers it is well worth persevering because of the in-depth coverage to which the various models are subjected, and also because of the extensive reference lists at the back of both volumes which direct readers to the various source references in the scientific literature. Thus, for the wider materials science scientific community the two volumes will be a valuable library resource. While I would have liked to see more comparison with experimental data on both ideal and 'real' heterogeneous materials than is provided by the author and a discussion of how to model strong nonlinear current--voltage behaviour in systems such as zinc oxide varistors, my overall

  9. Methane storage in advanced porous materials.

    Science.gov (United States)

    Makal, Trevor A; Li, Jian-Rong; Lu, Weigang; Zhou, Hong-Cai

    2012-12-01

    The need for alternative fuels is greater now than ever before. With considerable sources available and low pollution factor, methane is a natural choice as petroleum replacement in cars and other mobile applications. However, efficient storage methods are still lacking to implement the application of methane in the automotive industry. Advanced porous materials, metal-organic frameworks and porous organic polymers, have received considerable attention in sorptive storage applications owing to their exceptionally high surface areas and chemically-tunable structures. In this critical review we provide an overview of the current status of the application of these two types of advanced porous materials in the storage of methane. Examples of materials exhibiting high methane storage capacities are analyzed and methods for increasing the applicability of these advanced porous materials in methane storage technologies described. PMID:22990753

  10. Scaling Effects of Cr(VI) Reduction Kinetics. The Role of Geochemical Heterogeneity

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Li [Pennsylvania State Univ., State College, PA (United States); Li, Li [Pennsylvania State Univ., State College, PA (United States)

    2015-10-22

    The natural subsurface is highly heterogeneous with minerals distributed in different spatial patterns. Fundamental understanding of how mineral spatial distribution patterns regulate sorption process is important for predicting the transport and fate of chemicals. Existing studies about the sorption was carried out in well-mixed batch reactors or uniformly packed columns, with few data available on the effects of spatial heterogeneities. As a result, there is a lack of data and understanding on how spatial heterogeneities control sorption processes. In this project, we aim to understand and develop modeling capabilities to predict the sorption of Cr(VI), an omnipresent contaminant in natural systems due to its natural occurrence and industrial utilization. We systematically examine the role of spatial patterns of illite, a common clay, in determining the extent of transport limitation and scaling effects associated with Cr(VI) sorption capacity and kinetics using column experiments and reactive transport modeling. Our results showed that the sorbed mass and rates can differ by an order of magnitude due to of the illite spatial heterogeneities and transport limitation. With constraints from data, we also developed the capabilities of modeling Cr(VI) in heterogeneous media. The developed model is then utilized to understand the general principles that govern the relationship between sorption and connectivity, a key measure of the spatial pattern characteristics. This correlation can be used to estimate Cr(VI) sorption characteristics in heterogeneous porous media. Insights gained here bridge gaps between laboratory and field application in hydrogeology and geochemical field, and advance predictive understanding of reactive transport processes in the natural heterogeneous subsurface. We believe that these findings will be of interest to a large number of environmental geochemists and engineers, hydrogeologists, and those interested in contaminant fate and transport

  11. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    OpenAIRE

    De Lucia, M.; Kempka, T.; Kühn, M.

    2014-01-01

    Fully-coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i) that the presence of CO2 is the only driving force for chemical reactions and (ii) that its migration in the reservoir is only marginally affected by immobilization due to chemical reac...

  12. Visualizing Gas Adsorption on Porous Solids: Four Simple, Effective Demonstrations

    Science.gov (United States)

    Cheung, Ocean

    2014-01-01

    Gas adsorption on porous solids is a topic that is often discussed in an undergraduate chemistry or chemical engineering course. The idea of porosity and gas adsorption on a porous solid is usually discussed with adsorption isotherms recorded using commercially available equipment. This discussion can be rather abstract and can be difficult for…

  13. Natural Convection in Enclosed Porous or Fluid Media

    Science.gov (United States)

    Saatdjian, Esteban; Lesage, François; Mota, José Paulo B.

    2014-01-01

    In Saatdjian, E., Lesage, F., and Mota, J.P.B, "Transport Phenomena Projects: A Method to Learn and to Innovate, Natural Convection Between Porous, Horizontal Cylinders," "Chemical Engineering Education," 47(1), 59-64, (2013), the numerical solution of natural convection between two porous, concentric, impermeable cylinders was…

  14. High-quality elliptical iron glycolate nanosheets: selective synthesis and chemical conversion into FexOy nanorings, porous nanosheets, and nanochains with enhanced visible-light photocatalytic activity

    Science.gov (United States)

    Tong, Guoxiu; Liu, Yun; Wu, Tong; Ye, Yucheng; Tong, Chaoli

    2015-10-01

    This paper describes an original and facile polyol-mediated solvothermal synthesis of elliptical iron glycolate nanosheets (IGNSs) combined with precursor thermal conversion into γ-Fe2O3 and α-Fe2O3/γ-Fe2O3 porous nanosheets (PNSs), α-Fe2O3 nanochains (NCs), and elliptical Fe3O4 nanorings (NRs). The IGNSs were produced via the oxidation-reduction and co-precipitation reactions in the presence of iron(iii) salts, ethylene glycol, polyethylene glycol, and ethylenediamine. Control over Fe3+ concentration, temperature, and time can considerably modulate the size and phase of the products. The IGNSs can be transformed to γ-Fe2O3 and α-Fe2O3/γ-Fe2O3 PNSs, α-Fe2O3 NCs, and elliptical Fe3O4 NRs by heat treatment under various annealing temperatures and ambiences. The PNSs and NCs exhibited high soft magnetic properties and coercivity, respectively. Visible-light photocatalytic activity toward RhB in the presence of H2O2 by PNSs and NCs was phase-, SBET, size-, porosity-, and local structure-dependent, following the order: α-Fe2O3 NCs > α-Fe2O3/γ-Fe2O3 PNSs > γ-Fe2O3 PNSs > IGNSs. In particular, α-Fe2O3/γ-Fe2O3 PNSs possessed significantly enhanced photocatalytic activity with good recyclability and could be conveniently separated by an applied magnetic field because of high magnetization. We believe that the as-prepared α-Fe2O3/γ-Fe2O3 PNSs have potential practical use in waste water treatment and microwave absorption.This paper describes an original and facile polyol-mediated solvothermal synthesis of elliptical iron glycolate nanosheets (IGNSs) combined with precursor thermal conversion into γ-Fe2O3 and α-Fe2O3/γ-Fe2O3 porous nanosheets (PNSs), α-Fe2O3 nanochains (NCs), and elliptical Fe3O4 nanorings (NRs). The IGNSs were produced via the oxidation-reduction and co-precipitation reactions in the presence of iron(iii) salts, ethylene glycol, polyethylene glycol, and ethylenediamine. Control over Fe3+ concentration, temperature, and time can

  15. Two-Phase Flow in Heterogeneous Media

    CERN Document Server

    Ghaffari, Hamed O

    2009-01-01

    In this study, we investigate the appeared complexity of two-phase flow (air-water) in a heterogeneous soil where the supposed porous media is non-deformable media which is under the time-dependent gas pressure. After obtaining of governing equations and considering the capillary pressure-saturation and permeability functions, the evolution of the models unknown parameters were obtained. In this way, using COMSOL (FEMLAB) and fluid flow-script Module, the role of heterogeneity in intrinsic permeability was analysed. Also, the evolution of relative permeability of wetting and non-wetting fluid, capillary pressure and other parameters were elicited.

  16. Analysis Of Convective Plane Stagnation Point Chemically Reactive Mhd Flow Past A Vertical Porous Plate With A Convective Boundary Condition In The Presence Of A Uniform Magnetic Field.

    Directory of Open Access Journals (Sweden)

    Adeniyan, A.,

    2013-09-01

    Full Text Available The numerical investigation of a stagnation point boundary layer flow , mass and heat transfer of a steady two dimensional , incompressible , viscous electrically conducting, chemically reacting laminar fluid over a vertical convectively heated , electrically neutral flat plate exposed to a transverse uniform magnetic field has been carried out to examine the influence of the simultaneous presence of the effects of a convective boundary condition, chemical reaction, heat transfer and suction or injection. The governing coupled partial differential equations have been reduced to a set of coupled nonlinear ordinary differential equations by means of the similarity transformation , which has been solved using the classical fourth order Runge-Kutta method alongside with a shooting technique. The computational results have been presented by means of the table and discussed graphically. It has been observed that pertinent and invaluable engineering parameters such as the Skin-friction coefficient, the plate temperature distribution, the velocity , temperature and concentration profiles are appreciably influenced by flow parameters such as the magnetic field, convective heat parameters , Prandtl number, Sherwood number, Nusselt number, etc .

  17. The Effects of Variable Viscosity, Viscous Dissipation and Chemical Reaction on Heat and Mass Transfer Flow of MHD Micropolar Fluid along a Permeable Stretching Sheet in a Non-Darcian Porous Medium

    Directory of Open Access Journals (Sweden)

    A. M. Salem

    2013-01-01

    Full Text Available A numerical model is developed to study the effects of temperature-dependent viscosity on heat and mass transfer flow of magnetohydrodynamic(MHD micropolar fluids with medium molecular weight along a permeable stretching surface embedded in a non-Darcian porous medium in the presence of viscous dissipation and chemical reaction. The governing boundary equations for momentum, angular momentum (microrotation, and energy and mass transfer are transformed to a set of nonlinear ordinary differential equations by using similarity solutions which are then solved numerically by shooting technique. A comparison between the analytical and the numerical solutions has been included. The effects of the various physical parameters entering into the problem on velocity, microrotation, temperature and concentration profiles are presented graphically. Finally, the effects of pertinent parameters on local skin-friction coefficient, local Nusselt number and local Sherwood number are also presented graphically. One important observation is that for some kinds of mixtures (e.g., H2, air with light and medium molecular weight, the magnetic field and temperature-dependent viscosity effects play a significant role and should be taken into consideration as well.

  18. Heat and Mass Transfer Effects on Unsteady MHD Natural Convection Flow of a Chemically Reactive and Radiating Fluid through a Porous Medium Past a Moving Vertical Plate with Arbitrary Ramped Temperature

    Directory of Open Access Journals (Sweden)

    Gauri Shanker Seth

    2016-01-01

    Full Text Available Investigation of unsteady hydromagnetic natural convection flow with heat and mass transfer of a viscous, incompressible, electrically conducting, chemically reactive and optically thin radiating fluid past an exponentially accelerated moving vertical plate with arbitrary ramped temperature embedded in a fluid saturated porous medium is carried out. Exact solutions of momentum, energy and concentration equations are obtained in closed form by Laplace transform technique. The expressions for the shear stress, rate of heat transfer and rate of mass transfer at the plate for both ramped temperature and isothermal plates are derived. The numerical values of fluid velocity, fluid temperature and species concentration are displayed graphically whereas those of shear stress, rate of heat transfer and rate of mass transfer at the plate are presented in tabular form for various values of pertinent flow parameters. It is found that, for isothermal plate, the fluid temperature approaches steady state when t  1.5 . Consequently, the rate of heat transfer at isothermal plate approaches steady state when t  1.5 .

  19. Disordered hyperuniform heterogeneous materials.

    Science.gov (United States)

    Torquato, Salvatore

    2016-10-19

    Disordered hyperuniform many-body systems are distinguishable states of matter that lie between a crystal and liquid: they are like perfect crystals in the way they suppress large-scale density fluctuations and yet are like liquids or glasses in that they are statistically isotropic with no Bragg peaks. These systems play a vital role in a number of fundamental and applied problems: glass formation, jamming, rigidity, photonic and electronic band structure, localization of waves and excitations, self-organization, fluid dynamics, quantum systems, and pure mathematics. Much of what we know theoretically about disordered hyperuniform states of matter involves many-particle systems. In this paper, we derive new rigorous criteria that disordered hyperuniform two-phase heterogeneous materials must obey and explore their consequences. Two-phase heterogeneous media are ubiquitous; examples include composites and porous media, biological media, foams, polymer blends, granular media, cellular solids, and colloids. We begin by obtaining some results that apply to hyperuniform two-phase media in which one phase is a sphere packing in d-dimensional Euclidean space [Formula: see text]. Among other results, we rigorously establish the requirements for packings of spheres of different sizes to be 'multihyperuniform'. We then consider hyperuniformity for general two-phase media in [Formula: see text]. Here we apply realizability conditions for an autocovariance function and its associated spectral density of a two-phase medium, and then incorporate hyperuniformity as a constraint in order to derive new conditions. We show that some functional forms can immediately be eliminated from consideration and identify other forms that are allowable. Specific examples and counterexamples are described. Contact is made with well-known microstructural models (e.g. overlapping spheres and checkerboards) as well as irregular phase-separation and Turing-type patterns. We also ascertain a family

  20. In-situ characterization of heterogeneous catalysts

    CERN Document Server

    Rodriguez, Jose A; Chupas, Peter J

    2013-01-01

    Helps researchers develop new catalysts for sustainable fuel and chemical production Reviewing the latest developments in the field, this book explores the in-situ characterization of heterogeneous catalysts, enabling readers to take full advantage of the sophisticated techniques used to study heterogeneous catalysts and reaction mechanisms. In using these techniques, readers can learn to improve the selectivity and the performance of catalysts and how to prepare catalysts as efficiently as possible, with minimum waste. In-situ Characterization of Heterogeneous Catalysts feat

  1. Investigation of Heterogeneous Atmospheric Chlorine Chemistry: Modeling and Environmental Chamber Studies Authors: Cameron B. Faxon, Lea Hildebrandt Ruiz, and David Allen University of Texas at Austin, McKetta Department of Chemical Engineering

    Science.gov (United States)

    Faxon, C. B.; Hildebrandt Ruiz, L.; Allen, D.

    2013-12-01

    Previous work has shown that gas phase atomic chlorine radicals (Cl*) can influence tropospheric photochemistry, including concentrations of volatile organic compound (VOC) and ozone. These radicals are produced through both gas phase and heterogeneous pathways. This work presents computational and experimental investigation into the heterogeneous reactions of chloride aerosols. An overview of a sensitivity analysis of the physical parameters involved in the heterogeneous production of nitryl chloride (ClNO2) (R1-R5) will comprise the computational work presented. NO2(g) + NO3(g) ↔ N2O5(g) (R1) N2O5(aq) ↔ N2O5(aq) (R2) N2O5(aq) ↔ NO2+(aq) + NO3-(aq) (R3) NO2+(aq) + H2O(aq) → H3O+(aq) + HNO3(aq) (R4a) NO2+(aq) + Cl- → ClNO2 + H2O(aq) (R4b) NO3-(aq) + H+ ↔ HNO3+(aq) (R5) Relative parameters include the reactive uptake coefficient, ClNO2 yield, particle surface area, and gas phase concentrations of VOCs and NOx. The sensitivity analysis results were generated through photochemical box modeling and focus on the production of ClNO2 and impacts to ozone production. Results were compared to a base case scenario in which all heterogeneous reactions were absent. Parameter values reaching the upper limits reported in the literature were tested, and results indicate that ClNO2 chemistry can potentially change peak O3 concentrations by -10.5% to 27%. NOx availability was also found to play an important role. Experimental results of the heterogeneous reaction between OH* and particulate chloride (R6-R7) will also be discussed. The mechanism is shown below, and OH***Cl- represents an intermediate species forming at the particle surface. OH(g) + Cl-(aq) → OH***Cl-(aq) (R6) 2OH***Cl-(aq) → Cl2,g + 2OH-(aq) (R7) Environmental chamber experiments involving the exposure of NaCl aerosol particles to typical atmospheric conditions (HOx, NOx, O3 and UV radiation) were performed. A 10 cubic meter teflon reaction chamber equipped with UV lights was used to contain the

  2. Adsorption Kinetics in Nanoscale Porous Coordination Polymers

    Energy Technology Data Exchange (ETDEWEB)

    Nune, Satish K.; Thallapally, Praveen K.; McGrail, Benard Peter; Annapureddy, Harsha V. R.; Dang, Liem X.; Mei, Donghai; Karri, Naveen; Alvine, Kyle J.; Olszta, Matthew J.; Arey, Bruce W.; Dohnalkova, Alice

    2015-10-07

    Nanoscale porous coordination polymers were synthesized using simple wet chemical method. The effect of various polymer surfactants on colloidal stability and shape selectivity was investigated. Our results suggest that the nanoparticles exhibited significantly improved adsorption kinetics compared to bulk crystals due to decreased diffusion path lengths and preferred crystal plane interaction.

  3. Structure of random porous materials: Silica aerogel

    International Nuclear Information System (INIS)

    Using small-angle x-ray scattering, we show that porous silica aerogel has a fractal backbone structure. The observed structure is traced to the underlying chemical (polymerization) and physical (colloid aggregation) growth processes. Comparison of scattering curves for aerogel with silica aggregates confirms this interpretation

  4. Probabilistic human health risk assessment of degradation-related chemical mixtures in heterogeneous aquifers: risk statistics, hot spots, and preferential channels

    OpenAIRE

    Henri, Christopher Vincent; Fernández García, Daniel; Barros, Felipe de

    2015-01-01

    The increasing presence of toxic chemicals released in the subsurface has led to a rapid growth of social concerns and the need to develop and employ models that can predict the impact of groundwater contamination on human health risk under uncertainty. Monitored natural attenuation is a common remediation action in many contamination cases. However, natural attenuation can lead to the production of daughter species of distinct toxicity that may pose challenges in pollution management strateg...

  5. A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

    OpenAIRE

    De Lucia, M.; Kempka, T.; Kühn, M.

    2015-01-01

    Fully coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i) that the presence of CO2 is the only driving force for chemical reactions and (ii) that its migration in the reservoir is only marginally affected by immobilisation due to chem...

  6. Computational thermal, chemical, fluid, and solid mechanics for geosystems management.

    Energy Technology Data Exchange (ETDEWEB)

    Davison, Scott; Alger, Nicholas; Turner, Daniel Zack; Subia, Samuel Ramirez; Carnes, Brian; Martinez, Mario J.; Notz, Patrick K.; Klise, Katherine A.; Stone, Charles Michael; Field, Richard V., Jr.; Newell, Pania; Jove-Colon, Carlos F.; Red-Horse, John Robert; Bishop, Joseph E.; Dewers, Thomas A.; Hopkins, Polly L.; Mesh, Mikhail; Bean, James E.; Moffat, Harry K.; Yoon, Hongkyu

    2011-09-01

    This document summarizes research performed under the SNL LDRD entitled - Computational Mechanics for Geosystems Management to Support the Energy and Natural Resources Mission. The main accomplishment was development of a foundational SNL capability for computational thermal, chemical, fluid, and solid mechanics analysis of geosystems. The code was developed within the SNL Sierra software system. This report summarizes the capabilities of the simulation code and the supporting research and development conducted under this LDRD. The main goal of this project was the development of a foundational capability for coupled thermal, hydrological, mechanical, chemical (THMC) simulation of heterogeneous geosystems utilizing massively parallel processing. To solve these complex issues, this project integrated research in numerical mathematics and algorithms for chemically reactive multiphase systems with computer science research in adaptive coupled solution control and framework architecture. This report summarizes and demonstrates the capabilities that were developed together with the supporting research underlying the models. Key accomplishments are: (1) General capability for modeling nonisothermal, multiphase, multicomponent flow in heterogeneous porous geologic materials; (2) General capability to model multiphase reactive transport of species in heterogeneous porous media; (3) Constitutive models for describing real, general geomaterials under multiphase conditions utilizing laboratory data; (4) General capability to couple nonisothermal reactive flow with geomechanics (THMC); (5) Phase behavior thermodynamics for the CO2-H2O-NaCl system. General implementation enables modeling of other fluid mixtures. Adaptive look-up tables enable thermodynamic capability to other simulators; (6) Capability for statistical modeling of heterogeneity in geologic materials; and (7) Simulator utilizes unstructured grids on parallel processing computers.

  7. Porous Silicon & Titanium Dioxide Coatings Prepared by Atmospheric Pressure Plasma Jet Chemical Vapour Deposition Technique-A Novel Coating Technology for Photovoltaic Modules

    Directory of Open Access Journals (Sweden)

    S. Bhatt

    2011-01-01

    Full Text Available Atmospheric Pressure Plasma Jet (APPJ is an alternative for wet processes used to make anti reflection coatings and smooth substrate surface for the PV module. It is also an attractive technique because of it’s high growth rate, low power consumption, lower cost and absence of high cost vacuum systems. This work deals with the deposition of silicon oxide from hexamethyldisiloxane (HMDSO thin films and titanium dioxide from tetraisopropyl ortho titanate using an atmospheric pressure plasma jet (APPJ system in open air conditions. A sinusoidal high voltage with a frequency between 19-23 kHz at power up to 1000 W was applied between two tubular electrodes separated by a dielectric material. The jet, characterized by Tg ~ 600-800 K, was mostly laminar (Re ~ 1200 at the nozzle exit and became partially turbulent along the jet axis (Re ~ 3300. The spatially resolved emission spectra showed OH, N2, N2+ and CN molecular bands and O, H, N, Cu and Cr lines as well as the NO2 chemiluminescence continuum (450-800 nm. Thin films with good uniformity on the substrate were obtained at high deposition rate, between 800 -1000 nm.s-1, and AFM results revealed that coatings are relatively smooth (Ra ~ 2 nm. The FTIR and SEM analyses were better used to monitor the chemical composition and the morphology of the films in function of the different experimental conditions.

  8. Spectroscopic properties of porous silicon

    International Nuclear Information System (INIS)

    The research of composition and spectroscopic properties of porous silicon (por-Si) surface has been done. Complex of photoluminescence (PL), electroluminescence (EL), Auger electron spectroscopy (AES), thermostimulated exoelectron emission (TSEE), electron spin resonance (ESR) spectroscopy methods have been applied to study the chemical composition of the surface, that plays a decisive role in light-emitting properties of pot-Si. The studies were done on the composition of por-Si real surface containing pure silicon or SiHy species mixture with silicon oxides and carbon atoms as well as background impurities of chlorine, fluorine and nitrogen. (author)

  9. Positronium chemistry in porous adsorbents

    International Nuclear Information System (INIS)

    Kinetic studies on the annihilation of orthopositronium in porous adsorbents have been performed using lifetime spectroscopy. The positron source applied was 22Na with 0.2 MBq activity. The adsorbents investigated were silica gels of different particle size and pore structure. The appearance of the long-lived component in the lifetime spectra can be explained by the diffusion of the orthopositronium into the pores affected by the particle size and the pore size of the adsorbent, the coverage on it and the chemical nature of the adsorbate. The long-term aim of the work is to determine and to explain these effects. (author)

  10. Denitrification and chemotaxis of Pseudomonas stutzeri KC in porous media.

    Science.gov (United States)

    Roush, Caroline J; Lastoskie, Christian M; Worden, R Mark

    2006-01-01

    Chemotaxis is an important mechanism by which microorganisms are dispersed in porous media. A vigorous chemotactic response to concentration gradients formed by microbial consumption of chemoattractants can accelerate transport of bacteria to highly contaminated regions of soils and sediments, enhancing the efficiency of in situ bioremediation operations. Although chemotaxis plays a key role in establishment of biodegradation zones in the subsurface, the effects of physical heterogeneity on bacterial motility are poorly understood. To investigate the influence of porous media heterogeneity on microbial chemotaxis, swarm plate migration experiments were conducted using Pseudomonas stutzeri strain KC, a denitrifying bacterium used for in situ biodegradation of carbon tetrachloride in groundwater. Swarm plate measurements indicate that strain KC is strongly chemotactic toward both acetate and nitrate. A three-component mathematical model was developed to describe the migration of strain KC. Estimates of chemotactic sensitivity were obtained in the homogeneous (agar) phase and in a heterogeneous medium of aquifer solids extracted from the Schoolcraft bioremediation field site in western Michigan. Interestingly, the motility of strain KC is significantly larger in the porous medium than in the aqueous phase. We hypothesize that chemotactic response is enhanced within the heterogeneous medium because chemoattractant gradients formed by nitrate consumption are larger in the confined spaces of the porous medium than in unconfined agar solution. PMID:16760079

  11. Hierarchical Porous Structures

    Energy Technology Data Exchange (ETDEWEB)

    Grote, Christopher John [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-06-07

    Materials Design is often at the forefront of technological innovation. While there has always been a push to generate increasingly low density materials, such as aero or hydrogels, more recently the idea of bicontinuous structures has gone more into play. This review will cover some of the methods and applications for generating both porous, and hierarchically porous structures.

  12. Convection in porous media

    CERN Document Server

    Bejan, A

    2006-01-01

    Provides an introduction to convection in porous media, such as fibrous insulation, geological strata, and catalytic reactors. This third edition covers ""designed"" porous media, the theory of deformable media, modeling viscous dissipation in hyperporous media, and more. It is useful for researchers, practicing engineers and students.

  13. Porous media fluid transport and pore structure

    CERN Document Server

    Dullien, F A L

    1992-01-01

    This book examines the relationship between transport properties and pore structure of porous material. Models of pore structure are presented with a discussion of how such models can be used to predict the transport properties of porous media. Portions of the book are devoted to interpretations of experimental results in this area and directions for future research. Practical applications are given where applicable, and are expected to be useful for a large number of different fields, including reservoir engineering, geology, hydrogeology, soil science, chemical process engineering, biomedica

  14. An analysis of seismic attenuation in random porous media

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The attenuation of seismic wave in rocks has been one of the interesting research topics, but till now no poroelasticity models can thoroughly explain the strong attenuation of wave in rocks. In this paper, a random porous medium model is designed to study the law of wave propagation in complex rocks based on the theory of Biot poroelasticity and the general theory of stochastic process. This model sets the density of grain, porosity, permeability and modulus of frame as random parameters in space, and only one fluid infiltrates in rocks for the sake of better simulation effect in line with real rocks in earth strata. Numerical simulations are implemented. Two different inverse quality factors of fast P-wave are obtained by different methods to assess attenuation through records of virtual detectors in wave field (One is amplitude decay method in time domain and the other is spectral ratio method in frequency domain). Comparing the attenuation results of random porous medium with those of homogeneous porous medium, we conclude that the attenuation of seismic wave of homogeneous porous medium is far weaker than that of random porous medium. In random porous media, the higher heterogeneous level is, the stronger the attenuation becomes, and when heterogeneity σ = 0.15 in simulation, the attenuation result is consistent with that by actual observation. Since the central frequency (50 Hz) of source in numerical simulation is in earthquake band, the numerical results prove that heterogeneous porous structure is one of the important factors causing strong attenuation in real stratum at intermediate and low frequency.

  15. Coupling Hydrological and Geochemical Simulations to Assess Spatial Heterogeneity and Chemical Evolution of Groundwaters at Two Candidate Repository Sites in Sweden

    International Nuclear Information System (INIS)

    The chemical composition of groundwater surrounding a high level radioactive waste repository is of importance to many factors that affect repository performance. The geochemical characteristics of Swedish groundwater systems are governed by successive mixing events between several end-member waters during their paleogeographic evolution. An approach is proposed here to investigate the spatial and temporal evolution of groundwater geochemical conditions by coupling hydrogeological and geochemical models in a sequential way. The procedure combines hydrogeological results by others [1,2] of a discrete fracture network using CONNECTFLOW with a mixing and reaction-path simulation using PHREEQC. The hydrological results contain mixing proportions of four reference waters (a deep brine, glacial meltwater, marine water, and meteoric infiltration) at each time step and at every node of the 3D model domain. In this work, mixing fractions are fed into PHREEQC using software developed to build formatted input files and to extract the information from output files for subsequent plotting and analysis. The geochemical calculations included both chemical mixing and equilibrium reactions with selected minerals: calcite, chalcedony and an Fe(III) oxyhydroxide. Some results for the Forsmark site, about 170 km north of Stockholm, Sweden, are graphically presented. Cross sections, where each node is color-coded with respect to an important variable (pH, Eh or concentrations of main elements), are used to visualize the future evolution of the site. Sensitivity analyses were made to evaluate the effects of the different reactions and/or assumptions. The proposed methodology has proved useful for evaluating the future geochemical evolution of the repository sites and to increase the confidence in the site descriptions. (authors)

  16. Mechanics of fluids in porous media

    Science.gov (United States)

    Bear, Jacob; Corapcioglu, M. Yavuz

    Transport of quantities such as mass component of a phase and/or heat occurs in fields as diversified as petroleum reservoir engineering, groundwater hydraulics, soil mechanics, industrial filtration, water purification, wastewater treatment, soil drainage and irrigation, and geothermal energy production. In all these areas, scientists, engineers, and planners make use of mathematical models; these models describe the relevant transport processes that occur within controlled porous medium domains and enable forecasting of the future behavior of these domains in response to planned activities. The mathematical models, in turn, are based on the understanding of phenomena, often within the void space, and on theories that relate these phenomena to measurable quantities.Because of the pressing needs in areas of practical interest such as the development of groundwater energy storage and geothermal energy production, a vast amount of research in all these fields has contributed, especially in the last two decades, to our understanding and ability to describe transport phenomena in porous media. In recent years these research efforts have been significantly accelerated, attracting scientists from many disciplines. The practical needs of solving boundary value problems in heterogeneous domains, irregular boundaries, coupled phenomena and multiple dependent variables led to the development of a variety of powerful numerical techniques. The realization that fields are highly heterogeneous and that the degree of heterogeneity depends on the scale of the problem led to the introduction of stochastic concepts as an additional tool for the description of phenomena.

  17. New permeameter for geologic porous-media

    International Nuclear Information System (INIS)

    The use of a modified microbore HPLC/SFC system is described as an automated rapid-analysis permeameter for studying the interactions of liquid hazardous-waste leachates with low permeability geologic porous-media(1). Numerous advantages over currently described equipment for permeability and leachate/soil compatibility testing are shown. The system can operate in a constant pressure mode for generating precise and constant hydraulic-gradients on porous media samples, or in a constant flow-rate and mode. Both techniques allow continuous real-time monitoring of permeability changes. The system can also determine when steady-state baseline hydraulic conductivity of the porous media has been achieved and then automatically switch permeants for chemical interaction studies. The instrument continuously monitors and displays permeant flow-rate, permeameter cell pressure-drop and UV-VIS absorbance of contaminant species in solution

  18. Heterogeneous Metal Catalysts for Oxidation Reactions

    Directory of Open Access Journals (Sweden)

    Md. Eaqub Ali

    2014-01-01

    Full Text Available Oxidation reactions may be considered as the heart of chemical synthesis. However, the indiscriminate uses of harsh and corrosive chemicals in this endeavor are threating to the ecosystems, public health, and terrestrial, aquatic, and aerial flora and fauna. Heterogeneous catalysts with various supports are brought to the spotlight because of their excellent capabilities to accelerate the rate of chemical reactions with low cost. They also minimize the use of chemicals in industries and thus are friendly and green to the environment. However, heterogeneous oxidation catalysis are not comprehensively presented in literature. In this short review, we clearly depicted the current state of catalytic oxidation reactions in chemical industries with specific emphasis on heterogeneous catalysts. We outlined here both the synthesis and applications of important oxidation catalysts. We believe it would serve as a reference guide for the selection of oxidation catalysts for both industries and academics.

  19. Heterogeneous catalysis and the challenges of powering the planet, securing chemicals for civilised life, and clean efficient utilization of renewable feedstocks.

    Science.gov (United States)

    Thomas, John Meurig

    2014-07-01

    This article reviews, first, the prospects, practices and principles of generating solar fuels. It does so with an analysis of recent progress in the light-driven emission of H2 (and other fuels) as well as O2 from water. To place this challenge in perspective, some current practices entailing the use of well-proven solid catalysts developed for fossil-based feedstocks, are described. The massive differences between proven methods of generating fuel and chemicals from non-renewable and from solar radiation are emphasized with the aid of numerous quantitative examples. Whilst it is acknowledged that a key action in reducing the liberation of greenhouse gases (GHG) is to tackle the challenge of decreasing their evolution in power generation and in the production of steel, aluminium and other bulk commodities (metals, alloys, concrete and ceramics), nevertheless much can be done to diminish the emission of CO2 (and to use it as feedstock) through the agency of new, designed solid catalysts and microalgae. Solar-thermal converters are also attractive alternatives, even though they are more likely to be used centrally rather than in small modular units like 'artificial leaves,' some of which are promising for the purposes of generating energy (and perhaps fuel) in a delocalized, modular manner. PMID:24988917

  20. Heterogeneous Bunsen reaction : Analysis and experimental study of chemical absorption of sulfur dioxide and dissolution of iodine into aqueous reacting system

    International Nuclear Information System (INIS)

    Bunsen reaction is one of the three main reaction steps of Iodine-Sulphur (I-S) thermochemical water splitting process for production of hydrogen, utilizing nuclear heat. This complex multiphase-multispecies reaction has to be carried out optimally for harnessing the potential of I-S process for large scale production of hydrogen. Apart from strong influence of operating conditions, contacting scheme, reactor type and size have severe bearing on issues like overall process efficiency, product purity, separation, conversion etc. In this study sulphur dioxide (gas) and iodine (solid) are reacted in aqueous solution (liquid) with gas sparging and mechanical agitation at room temperature. Experimental results of this reacting ternary system are analyzed in terms of film theory of mass transfer. Chemical absorption of sulphur dioxide and enhanced dissolution of iodine solid into Bunsen reacting system are interpreted to deduce crucial engineering information like controlling resistance, regime, enhancement factor etc, which will help in selection of suitable contacting scheme and design of multiphase absorber-reactor for large-scale production of hydrogen. Behavior of this fluid-fluid-solid absorber - reactor can be construed kinetically as 'Fast psuedo first order reaction system'. (author)

  1. Fabricating porous silicon carbide

    Science.gov (United States)

    Shor, Joseph S. (Inventor); Kurtz, Anthony D. (Inventor)

    1994-01-01

    The formation of porous SiC occurs under electrochemical anodization. A sample of SiC is contacted electrically with nickel and placed into an electrochemical cell which cell includes a counter electrode and a reference electrode. The sample is encapsulated so that only a bare semiconductor surface is exposed. The electrochemical cell is filled with an HF electrolyte which dissolves the SiC electrochemically. A potential is applied to the semiconductor and UV light illuminates the surface of the semiconductor. By controlling the light intensity, the potential and the doping level, a porous layer is formed in the semiconductor and thus one produces porous SiC.

  2. FACADE SYSTEM MADE OF POROUS MATERIALS

    Directory of Open Access Journals (Sweden)

    Zhukov Aleksey Dmitrievich

    2012-10-01

    Full Text Available The proposed multi-component façade system is made of porous concretes employed both as bearing structures and for heat insulation and fireproofing purposes. The authors also provide their recommendations in respect of the mounting of the proposed façade system. The façade system considered in the article is composed of wall foam concrete blocks reinforced by basalt fibers (bearing elements of the structure, cellular concrete polystyrene (thermal insulation, and porous concrete (fireproofing and thermal insulation. Retained shuttering (in the fireproofing sections represents chrysolite cement sheets attached to the structures composed of glass-fiber plastic elements. The application of insulating porous concrete as a fireproofing material is based on the principle of adjustable stress-strained states of materials in the environment of variable pressure. This technology was developed at Moscow State University of Civil Engineering, and it was initially designated for the manufacturing of tailor-made products. The above concrete is also designated for retained shuttering and modified cavity masonry walls. Porous concrete that expands inside the fireproofing cavity ensures a tight contact both with the basic material and thermal insulation plates. The use of materials of the same origin (Portland cement means the formation of strong transition zones connecting the system components in the course of its hardening and further operation. The results of the thermotechnical calculation demonstrate that the thermal resistance registered on the surface of the wall that is 3 meters high (that has a 0.4 m fireproofing cavity is equal to 3.98 sq. m. C/Wt. The value of the coefficient of thermotechnical heterogeneity (r is equal to 0.86 with account for the thickness and thermal conductivity of point and linear elements. If the thermotechnical heterogeneity is taken into consideration, the thermal resistance of the proposed wall is equal to 3.42 m2 С/Wt.

  3. Porous structure formation in ion irradiated germanium

    International Nuclear Information System (INIS)

    The ion beam induced modification of amorphous germanium is characterised by the formation of voids close to the sample surface and the transformation into a sponge-like porous surface layer at high ion fluences. This extreme structural modification of the sample surface is independent of the (heavy) ion species used and accompanied by a strong volume expansion. Nevertheless, recently it was demonstrated that buried voids (and buried sponge-like layers) can be formed in the depth of the projected ion range, however, only for the irradiation with I-ions at high ion fluences. Thus, the ion species and their chemical properties seem to play an important role in the structural modification around the projected ion range. In this paper we investigate the influence of the ion species on the ion beam induced void formation in Ge for room temperature irradiation with 380 keV I- and Au-ions as a function of the ion fluence. Independent of the ion species, a strong volume expansion is observed caused by void formation and the transformation into a sponge-like porous surface layer. For both ion species used, the final porous layers are structurally identical as established by cross section and plan view electron microscopy investigations. Further ion irradiation of the sponge-like porous structure, however, leads to significant differences in the ion beam induced structural evolution. For the Au-ion irradiation the porous layer remains nearly unchanged, whereas for the irradiation with I-ions a transformation from sponge-like to netlike porous layers occurs which is accompanied again by an extreme volume expansion. The underlying mechanism will be discussed based on chemical properties of the implanted ions

  4. Applied heterogeneous catalysis

    International Nuclear Information System (INIS)

    This reference book explains the scientific principles of heterogeneous catalysis while also providing details on the methods used to develop commercially viable catalyst products. A section of the book presents reactor design engineering theory and practices for the profitable application of these catalysts in large-scale industrial processes. A description of the mechanisms and commercial applications of catalysis is followed by a review of catalytic reaction kinetics. There are five chapters on selecting catalyst agents, developing and preparing industrial catalysts, measuring catalyst properties, and analyzing the physico-chemical characteristics of solid catalyst particles. The final chapter reviews the elements of catalytic reactor design, with emphasis on flow regimes vs. reactor types, heat and mass transfer in reactor beds, single- and multi-phase flows, and the effects of thermodynamics and other catalyst properties on the process flow scheme

  5. Heterogeneity and Microeconometrics Modelling

    DEFF Research Database (Denmark)

    Browning, Martin; Carro, Jesus

    Presented at the 2005 Econometric Society World Congress Plenary Session on "Modelling Heterogeneity". We survey the treatment of heterogeneity in applied microeconometrics analyses. There are three themes. First, there is usually much more heterogeneity than empirical researchers allow for. Seco...... structures. The latter task is one for economists: "heterogeneity is too important to be left to the statisticians". The paper concludes with a report of our own research on dynamic discrete choice models that allow for maximal heterogeneity...

  6. Stochastic PDE's for water flow, solute transport and wave propagation phenomena in heterogeneous geologic media.

    OpenAIRE

    Ababou, Rachid

    2013-01-01

    This lecture will present stochastic PDE's (Partial Differential Equations) to model various "transport" phenomena like water flow, solute transport and wave propagation, in heterogeneous geologic porous media. The material properties are represented by random functions of space F(x) (random fields). The resulting transport PDE’s contain random field coefficients, and their solutions are stochastic (randomly heterogeneous).

  7. Tracer transfer in consolidated porous medium and fractured porous medium: experimentations and modelling

    International Nuclear Information System (INIS)

    We try to identify and model physical and chemical mechanisms governing the water flow and the solute transport in fractured consolidated porous medium. An original experimental device was built. The 'cube' consists of an idealized fractured medium reproduced by piling up consolidated porous cubes of 5 cm edge. Meanwhile, columns of the homogeneous consolidated porous medium are studied. The same anionic tracing technique is used in both cases. Using a system analysis approach, we inject concentration pulses in the device to obtain breakthrough curves. After identifying the mass balance and the residence time, we fit the CD and the MIM models to the experimental data. The MIM model is able to reproduce experimental curves of the homogeneous consolidated porous medium better than the CD model. The mobile water fraction is in accordance with the porous medium geometry. The study of the flow rate influence highlights an interference dispersion regime. It was not possible to highlight the observation length influence in this case. On the contrary, we highlight the effect of the observation scale on the fractured and porous medium, comparing the results obtained on a small 'cube' and a big 'cube'. The CD model is not satisfactory in this case. Even if the MIM model can fit the experimental breakthrough curves, it was not possible to obtain unique parameters for the set of experiments. (author)

  8. Chemical microreactor and method thereof

    Energy Technology Data Exchange (ETDEWEB)

    Morse, Jeffrey D. (Martinez, CA); Jankowski, Alan (Livermore, CA)

    2011-08-09

    A method for forming a chemical microreactor includes forming at least one capillary microchannel in a substrate having at least one inlet and at least one outlet, integrating at least one heater into the chemical microreactor, interfacing the capillary microchannel with a liquid chemical reservoir at the inlet of the capillary microchannel, and interfacing the capillary microchannel with a porous membrane near the outlet of the capillary microchannel, the porous membrane being positioned beyond the outlet of the capillary microchannel, wherein the porous membrane has at least one catalyst material imbedded therein.

  9. Metal filled porous carbon

    Science.gov (United States)

    Gross, Adam F.; Vajo, John J.; Cumberland, Robert W.; Liu, Ping; Salguero, Tina T.

    2011-03-22

    A porous carbon scaffold with a surface and pores, the porous carbon scaffold containing a primary metal and a secondary metal, where the primary metal is a metal that does not wet the surface of the pores of the carbon scaffold but wets the surface of the secondary metal, and the secondary metal is interspersed between the surface of the pores of the carbon scaffold and the primary metal.

  10. Combustion within Porous Waste

    OpenAIRE

    Pfahl, Ulrich; Shepherd, Joseph E.; Unal, Cetin

    1998-01-01

    Flammable gases (primarily hydrogen and nitrous oxide but also ammonia and methane) are continuously being generated within the waste contained in the tank farms at Hanford Site. Some portions of the waste are porous and conceivably, a combustion event could occur within the waste due to accidental ignition. This has been postulated as a potential hazard since deflagrations and detonations are observed in laboratory experiments to propagate through combustible gases in porous materials, or ...

  11. Effects of Post-SiH4 and Plasma Treatments on Chemical Vapor Deposited Cu Seeds with Chemical Vapor Deposited TiN Barrier in Porous Low Dielectric Constant and Cu Integration

    Science.gov (United States)

    Pyo, Sung Gyu; Park, Shangkyun; Park, Hansoo; Lee, Donghyun

    2011-07-01

    A Cu seed deposited by chemical vapor deposition (CVD) was integrated with a CVD TiN barrier and electroplated Cu in a double level metal interconnect scheme using a dual damascene process. The post-SiH4 treatment of CVD TiN inhibits agglomeration of thin Cu by improving the wettability of Cu seeds as well as reducing the TiN sheet resistance. Post-plasma treatment on CVD Cu seeds decreases impurities in CVD Cu and eliminates interface voids between the CVD Cu seed and electroplated Cu, improving the gap filling properties of electroplated Cu layers. Inherently poor adhesion of the CVD Cu layers between the Cu barrier metal and the electroplated Cu is overcome by CVD TiN post treatments and CVD Cu post-plasma treatment. Bias-thermal-stress (BTS) tests were performed to verify the effect of post-SiH4 treatment. The SiH4 treated CVD TiN barrier and CVD Cu seed show feasibility for 65-nm technology in terms of low via resistance and chain yields.

  12. Dispersivity in heterogeneous permeable media

    International Nuclear Information System (INIS)

    When one fluid displaces another through a one-dimensional porous medium, the composition changes from pure displacing fluid at the inlet to pure displaced fluid some distance downstream. The distance over which an arbitrary percentage of this change occurs is defined as the mixing zone length, which increases with increasing average distance traveled by the displacement front. For continuous injection, the mixing zone size can be determined from a breakthrough curve as the time required for the effluent displacing fluid concentration to change from, say, 10% to 90%. In classical dispersion theory, the mixing zone grows in proportion to the square root of the mean distance traveled, or, equivalently, to the square root of the mean breakthrough time. In a multi-dimensional heterogeneous medium, especially at field scales, the size of the mixing zone grows almost linearly with mean distance or travel time. If an observed breakthrough curve is forced to fit the, clinical theory, the resulting effective dispersivity, instead of being constant, also increases almost linearly with the spatial or temporal scale of the problem. This occurs because the heterogeneity in flow properties creates a corresponding velocity distribution along the different flow pathways from the inlet to the outlet of the system. Mixing occurs mostly at the outlet, or wherever the fluid is sampled, rather than within the medium. In this paper, we consider the effects. of this behavior on radionuclide or other contaminant migration

  13. Dispersivity in heterogeneous permeable media

    International Nuclear Information System (INIS)

    When one fluid displaces another through a one-dimensional porous medium, the composition changes from pure displacing fluid at the inlet to pure displaced fluid some distance downstream. The distance over which an arbitrary percentage (typically 80%) of this change occurs is defined as the mixing zone length, which increases with increasing average distance traveled by the displacement front. Alternatively, for continuous injection, the mixing zone size can be determined from a breakthrough curve as the time required for the effluent displacing fluid concentration to change from, say, 10% to 90%. In classical dispersion theory, the mixing zone grows in proportion to the square root of the mean distance traveled, or, equivalently, to the square root of the mean breakthrough time. In a multi-dimensional heterogeneous medium, especially at field scales, the size of the mixing zone grows almost linearly with mean distance or travel time. If an observed breakthrough curve is forced to fit the classical theory, the resulting effective dispersivity, instead of being constant, also increases almost linearly with the spatial or temporal scale of the problem. This occurs because the heterogeneity in flow properties creates a corresponding velocity distribution along the different flow pathways from the inlet to the outlet of the system. Mixing occurs mostly at the outlet, or wherever the fluid is sampled, rather than within the medium. In this paper, we consider the effects of this behavior on radionuclide or other contaminant migration

  14. Film boiling on porous layered brass sphere during quenching

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Jun-young; Kim, Seol Ha; Jo, Hangjin; Lee, Gi Cheol; Kiyofumi, Moriyama; Park, Hyun Sun [POSTECH, Pohang (Korea, Republic of); Kim, Moo Hwan [KOREA Institute of Nuclear Safety, Daejeon (Korea, Republic of)

    2015-05-15

    Fluid (liquid or gas) can afford to be permeable into porous layer on heat transfer surface and this phenomenon significantly affects phase-change heat transfer, especially boiling. The Corrosion Residual Unidentified Deposition (CRUD) which has generally micro-scaled pore geometry could have considered as porous layer and it was suggested that modification of heat transfer surface like CRUD can influence cooling rate during Loss-Of-Coolant Accident (LOCA) transient. Therefore, role of porous layer will be more emphasized at core-safety analysis, because, recently strategy of nuclear-fuel operation gradually becomes higher burn-up and longer cycle. As another aspect, study about film boiling has widely concerned due to its importance at core-coolability in LOCA, however, consideration of porous layer has relatively restricted because of difficulty of fabrication, excepting for horizontal surface. In this article, we briefly introduce experimental result of film boiling on porous layered surface during quenching. Laboratory-scaled quenching facility was applied and porous layer was fabricated by Electro-Chemical Deposition (ECD) method at spherical brass test section. We observed that the existence of porous layer on heat transfer surface considerable affected the cooling rate (t{sub cool,MPS}/t{sub cool,BBS}-12) during quenching in a saturated distilled water, therefore, it is expected that porous layer like CURD may have the potential able to affect LOCA transient.

  15. Neural Approach for Calculating Permeability of Porous Medium

    Institute of Scientific and Technical Information of China (English)

    ZHANG Ji-Cheng; LIU Li; SONG Kao-Ping

    2006-01-01

    @@ Permeability is one of the most important properties of porous media. It is considerably difficult to calculate reservoir permeability precisely by using single well-logging response and simple formula because reservoir is of serious heterogeneity, and well-logging response curves are badly affected by many complicated factors underground. We propose a neural network method to calculate permeability of porous media. By improving the algorithm of the back-propagation neural network, convergence speed is enhanced and better results can be achieved. A four-layer back-propagation network is constructed to effectively calculate permeability from well log data.

  16. Hydrodynamic dispersion within porous biofilms.

    Science.gov (United States)

    Davit, Y; Byrne, H; Osborne, J; Pitt-Francis, J; Gavaghan, D; Quintard, M

    2013-01-01

    Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behavior by controlling nutrient supply, evacuation of waste products, and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilm-scale in the case where the width of the channels is significantly smaller than the thickness of the biofilm. We show that solute transport may be described via two coupled partial differential equations or telegrapher's equations for the averaged concentrations. These models are particularly relevant for chemicals, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterized by a second-order tensor whose components depend on (1) the topology of the channels' network; (2) the solute's diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion dominated, this analysis shows that hydrodynamic dispersion effects may significantly contribute to transport. PMID:23410370

  17. Microelectromechanical pump utilizing porous silicon

    Science.gov (United States)

    Lantz, Jeffrey W.; Stalford, Harold L.

    2011-07-19

    A microelectromechanical (MEM) pump is disclosed which includes a porous silicon region sandwiched between an inlet chamber and an outlet chamber. The porous silicon region is formed in a silicon substrate and contains a number of pores extending between the inlet and outlet chambers, with each pore having a cross-section dimension about equal to or smaller than a mean free path of a gas being pumped. A thermal gradient is provided along the length of each pore by a heat source which can be an electrical resistance heater or an integrated circuit (IC). A channel can be formed through the silicon substrate so that inlet and outlet ports can be formed on the same side of the substrate, or so that multiple MEM pumps can be connected in series to form a multi-stage MEM pump. The MEM pump has applications for use in gas-phase MEM chemical analysis systems, and can also be used for passive cooling of ICs.

  18. The Flow of Saturated Vapors through Porous Vycor Glass

    Czech Academy of Sciences Publication Activity Database

    Loimer, T.; Uchytil, Petr; Petričkovič, Roman; Setničková, Kateřina

    - : -, 2009 - (Egrican, N.; Mohamad, A.), s. 126-131 ISBN N. [International Conference on Applications of Porous Media /4./. Istanbul (TR), 10.08.2009-12.08.2009] R&D Projects: GA ČR GA104/09/1165 Institutional research plan: CEZ:AV0Z40720504 Keywords : saturated vapors * porous vycor glass * experimental data Subject RIV: CI - Industrial Chemistry, Chemical Engineering http://icapm2009.yeditepe.edu.tr/

  19. Ultimate permeation across atomically thin porous graphene.

    Science.gov (United States)

    Celebi, Kemal; Buchheim, Jakob; Wyss, Roman M; Droudian, Amirhossein; Gasser, Patrick; Shorubalko, Ivan; Kye, Jeong-Il; Lee, Changho; Park, Hyung Gyu

    2014-04-18

    A two-dimensional (2D) porous layer can make an ideal membrane for separation of chemical mixtures because its infinitesimal thickness promises ultimate permeation. Graphene--with great mechanical strength, chemical stability, and inherent impermeability--offers a unique 2D system with which to realize this membrane and study the mass transport, if perforated precisely. We report highly efficient mass transfer across physically perforated double-layer graphene, having up to a few million pores with narrowly distributed diameters between less than 10 nanometers and 1 micrometer. The measured transport rates are in agreement with predictions of 2D transport theories. Attributed to its atomic thicknesses, these porous graphene membranes show permeances of gas, liquid, and water vapor far in excess of those shown by finite-thickness membranes, highlighting the ultimate permeation these 2D membranes can provide. PMID:24744372

  20. Reactive Transport Modeling of CO2-induced Porosity and Permeability Changes in Heterogeneous Carbonate Rocks

    Science.gov (United States)

    Hao, Y.; Smith, M. M.; Mason, H. E.; Carroll, S.

    2015-12-01

    It has long been appreciated that chemical interactions have a major effect on rock porosity and permeability evolution and may alter the behavior or performance of both natural and engineered reservoir systems. Such reaction-induced permeability evolution is of particular importance for geological CO2 sequestration and storage associated with enhanced oil recovery. In this study we used a three-dimensional Darcy scale reactive transport model to simulate CO2 core flood experiments in which the CO2-equilibrated brine was injected into dolostone cores collected from the Arbuckle carbonate reservoir, Wellington, Kansas. Heterogeneous distributions of macro pores, fractures, and mineral phases inside the cores were obtained from X-ray computed microtomography (XCMT) characterization data, and then used to construct initial model macroscopic properties including porosity, permeability, and mineral compositions. The reactive transport simulations were performed by using the Nonisothermal Unsaturated Flow and Transport (NUFT) code, and their results were compared with experimental data. It was observed both experimentally and numerically that the dissolution fronts became unstable in highly heterogeneous and less permeable formations, leading to the development of highly porous flow paths or wormholes. Our model results indicate that the continuum-scale reactive transport models are able to adequately capture the evolution of distinct dissolution fronts as observed in carbonate rocks at a core scale. The impacts of rock heterogeneity, chemical kinetics and porosity-permeability relationships were also examined in this study. The numerical model developed in this study will not only help improve understanding of coupled physical and chemical processes controlling carbonate dissolution, but also provide a useful basis for upscaling transport and reaction properties from core scale to field scale. This work was performed under the auspices of the U.S. Department of Energy

  1. Porous multi-component material for the capture and separation of species of interest

    Energy Technology Data Exchange (ETDEWEB)

    Addleman, Raymond S.; Chouyyok, Wilaiwan; Li, Xiaohong S.; Cinson, Anthony D.; Gerasimenko, Aleksandr A

    2016-06-21

    A method and porous multi-component material for the capture, separation or chemical reaction of a species of interest is disclosed. The porous multi-component material includes a substrate and a composite thin film. The composite thin film is formed by combining a porous polymer with a nanostructured material. The nanostructured material may include a surface chemistry for the capture of chemicals or particles. The composite thin film is coupled to the support or device surface. The method and material provides a simple, fast, and chemically and physically benign way to integrate nanostructured materials into devices while preserving their chemical activity.

  2. Porous hydroxyapatite for artificial bone applications

    OpenAIRE

    I. Sopyan et al

    2007-01-01

    Hydroxyapatite (HA) has been used clinically for many years. It has good biocompatibility in bone contact as its chemical composition is similar to that of bone material. Porous HA ceramics have found enormous use in biomedical applications including bone tissue regeneration, cell proliferation, and drug delivery. In bone tissue engineering it has been applied as filling material for bone defects and augmentation, artificial bone graft material, and prosthesis revision surgery. Its high surfa...

  3. Shock wave induced vaporization of porous solids

    OpenAIRE

    Shen, Andy H.; Ahrens, Thomas J.; O'Keefe, John D.

    2003-01-01

    Strong shock waves generated by hypervelocity impact can induce vaporization in solid materials. To pursue knowledge of the chemical species in the shock-induced vapors, one needs to design experiments that will drive the system to such thermodynamic states that sufficient vapor can be generated for investigation. It is common to use porous media to reach high entropy, vaporized states in impact experiments. We extended calculations by Ahrens [J. Appl. Phys. 43, 2443 (1972)] and Ahrens and O'...

  4. Heterogeneous Catalyst Deactivation and Regeneration: A Review

    OpenAIRE

    Morris D. Argyle; Calvin H. Bartholomew

    2015-01-01

    Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with referen...

  5. Sucrose Inversion An Experiment on Heterogeneous Catalysis

    OpenAIRE

    Adélio Mendes; Magalhães, Fernão D.; Luis M. Madeira

    2003-01-01

    llustration of heterogeneous catalysis concepts in laboratory courses is not usually simple or economical. For our undergraduate senior lab course we have developed an environmentally friendly experiment dealing with several aspects of heterogeneous catalysis, having in mind the use of readily available and relatively inexpensive equipment, and chemicals on a compact setup, which students can safely operate. The experiment deals with the acid-catalyzed sucrose inversion, performed in packed b...

  6. A heterogeneous multiscale method for poroelasticity

    Science.gov (United States)

    Delgado, Paul M.

    In this thesis, we develop and analyze a heterogeneous multiscale model for coupled fluid flow and solid deformation in porous media based on operator splitting and finite volume method. The splitting method results in two elliptic multiscale PDE's in the form of a reaction diffusion equation and a linear elasticity equation. We extend our previous multiscale method from 1D to higher dimensions and develop new approaches for the inclusion of mixed boundary conditions and source terms. We derive an error estimate for our multiscale method and analyze the stability of our splitting method. We also test the effectiveness of our method in the case of steady state linear poroelasticity.

  7. Optical measurements of chemically heterogeneous particulate surfaces

    Science.gov (United States)

    Zubko, Nataliya; Gritsevich, Maria; Zubko, Evgenij; Hakala, Teemu; Peltoniemi, Jouni I.

    2016-07-01

    We experimentally study light scattering by particulate surfaces consisting of two high-contrast materials. Using the Finnish Geodetic Institute field goniospectropolarimeter, reflectance and degree of linear polarization are measured in dark volcanic sand, bright salt (NaCl) and bright ferric sulfate (Fe2(SO4)3); and in mixtures of bright and dark components. We found that the light-scattering response monotonically changes with volume ratio of dark and bright components. In contrast to previous finding, we do not detect an enhancement of the negative polarization amplitude in two-component high-contrast mixtures. Two-component mixtures reveal an inverse correlation between maximum of their linear polarization and reflectance near backscattering, the so-called Umov effect. In log-log scales this inverse correlation takes a linear form for the dark and moderate-dark samples, while for the brightest samples there is a noticeable deviation from the linear trend.

  8. Overview of medium heterogeneity and transport processes

    International Nuclear Information System (INIS)

    Medium heterogeneity can have significant impact on the behavior of solute transport. Tracer breakthrough curves from transport in a heterogeneous medium are distinctly different from that in a homogeneous porous medium. Usually the shape of the breakthrough curves are highly non-symmetrical with a fast rise at early times and very long tail at late times, and often, they consist of multiple peaks. Moreover, unlike transport in a homogeneous medium where the same transport parameters describe the entire medium, transport through heterogeneous media gives rise to breakthrough curves which have strong spatial dependence. These inherent characteristics of transport in heterogeneous medium present special challenge to the performance assessment of a potential high level nuclear waste repository with respect to the possible release of radio nuclides to the accessible environment. Since an inherently desirable site characteristic for a waste repository is that flow and transport should be slow, then transport measurements in site characterization efforts will necessarily be spatially small and temporally short compare to the scales which are of relevance to performance assessment predictions. In this paper we discuss the role of medium heterogeneity in site characterization and performance assessment. Our discussion will be based on a specific example of a 3D heterogeneous stochastic model of a site generally similar to, the Aespoe Island, the site of the Hard Rock Laboratory in Southern Sweden. For our study, alternative 3D stochastic fields of hydraulic conductivities conditioned on ''point'' measurements shall be generated. Results of stochastic flow and transport simulations would be used to address the issues of (1) the relationship of tracer breakthrough with the structure of heterogeneity, and (2) the inference from small scale testing results to large scale and long term predictions

  9. Modeling of Flow, Transport and Controlled Sedimentation Phenomena during Mixing of Salt Solutions in Complex Porous Formations

    Science.gov (United States)

    Skouras, Eugene D.; Jaho, Sofia; Pavlakou, Efstathia I.; Sygouni, Varvara; Petsi, Anastasia; Paraskeva, Christakis A.

    2015-04-01

    The deposition of salts in porous media is a major engineering phenomenon encountered in a plethora of industrial and environmental applications where in some cases is desirable and in other not (oil production, geothermal systems, soil stabilization etc). Systematic approach of these problems requires knowledge of the key mechanisms of precipitating salts within the porous structures, in order to develop new methods to control the process. In this work, the development and the solution of spatiotemporally variable mass balances during salt solution mixing along specific pores were performed. Both analytical models and finite differences CFD models were applied for the study of flow and transport with simultaneous homogeneous and heterogeneous nucleation (by crystal growth on the surface of the pores) in simple geometries, while unstructured finite elements and meshless methods were developed and implemented for spatial discretization, reconstruction, and solution of transport equations and homogeneous / heterogeneous reactions in more complex geometries. At initial stages of this work, critical problem parameters were identified, such as the characteristics of the porosity, the number of dissolved components, etc. The parameters were then used for solving problems which correspond to available experimental data. For each combination of ions and materials, specific data and process characteristics were included: (a) crystal kinetics (nucleation, growth rates or reaction surface rates of crystals, critical suspension concentrations), (b) physico-chemical properties (bulk density, dimensions of generated crystals, ion diffusion coefficients in the solution), (c) operating parameters (macroscopic velocity, flow, or pressure gradient of the solution, ion concentration) (d) microfluidic data (geometry, flow area), (e) porosity data in Darcy description (initial porosity, specific surface area, tortuosity). During the modeling of flow and transport in three

  10. Foams in porous media

    Energy Technology Data Exchange (ETDEWEB)

    Marsden, S.S.

    1986-07-01

    In 1978 a literature search on selective blocking of fluid flow in porous media was done by Professor S.S. Marsden and two of his graduate students, Tom Elson and Kern Huppy. This was presented as SUPRI Report No. TR-3 entitled ''Literature Preview of the Selected Blockage of Fluids in Thermal Recovery Projects.'' Since then a lot of research on foam in porous media has been done on the SUPRI project and a great deal of new information has appeared in the literature. Therefore we believed that a new, up-to-date search should be done on foam alone, one which would be helpful to our students and perhaps of interest to others. This is a chronological survey showing the development of foam flow, blockage and use in porous media, starting with laboratory studies and eventually getting into field tests and demonstrations. It is arbitrarily divided into five-year time periods. 81 refs.

  11. Diffusion in heterogeneous media

    Science.gov (United States)

    Zhang, Y.; Liu, L.

    2012-12-01

    Diffusion in heterogeneous media has been investigated for over forty years. However, the fundamental equations for bulk (effective) diffusivity in multi-phase systems were incorrect because of the use of an inappropriate similarity between diffusion and other physical properties such as thermal conductivity. The mistake has permeated through the literature and textbooks. Specifically, the role of concentration partitioning between different phases in diffusion was not considered in such similarity relations. In this work, we present the correct method to derive such relations in heterogeneous media. Barrer [1] used the similarity between diffusivity and thermal conductivity to derive the relation between the bulk (effective) diffusivity and the individual-phase diffusivities. The approach was followed by many others [2-4]. Unfortunately the similarity approach by Barrer [1] is incorrect because there is also dissimilarity. The key difference is that, even though heat conduction and mass diffusion are characterized by a similar flux equation, in heat conduction, T is continuous across phase boundaries, whereas in diffusion, C is usually not continuous across phase boundaries. The concentration in each phase plays a major role in controlling the contribution by the phase to the bulk diffusive flux and hence the bulk diffusivity. For example, if the concentration of a component in a phase is very low, even if the diffusivity in the phase is high, the contribution of diffusion in that phase to the bulk diffusion flux can still be negligible. Hence, previous models for diffusivity in composite materials or multi-mineral rocks, no matter how sophisticated, are fundamentally wrong because the foundation is a mistake. Correcting the mistake is straightforward. The mass flux can be written in terms of chemical potential and mobility [5,6]. Because chemical potential is continuous across phase boundaries, the relation between bulk mobility and individual-phase mobilities is

  12. Porous silicon gettering

    Energy Technology Data Exchange (ETDEWEB)

    Tsuo, Y.S.; Menna, P.; Pitts, J.R. [National Renewable Energy Lab., Golden, CO (United States)] [and others

    1996-05-01

    The authors have studied a novel extrinsic gettering method that uses the large surface areas produced by a porous-silicon etch as gettering sites. The annealing step of the gettering used a high-flux solar furnace. They found that a high density of photons during annealing enhanced the impurity diffusion to the gettering sites. The authors used metallurgical-grade Si (MG-Si) prepared by directional solidification casing as the starting material. They propose to use porous-silicon-gettered MG-Si as a low-cost epitaxial substrate for polycrystalline silicon thin-film growth.

  13. Understanding generalized inversions of nuclear magnetic resonance transverse relaxation time in porous media

    International Nuclear Information System (INIS)

    The nuclear magnetic resonance transverse relaxation time T2, measured using the Carr-Purcell-Meiboom-Gill (CPMG) experiment, is a powerful method for obtaining unique information on liquids confined in porous media. Furthermore, T2 provides structural information on the porous material itself and has many applications in petrophysics, biophysics, and chemical engineering. Robust interpretation of T2 distributions demands appropriate processing of the measured data since T2 is influenced by diffusion through magnetic field inhomogeneities occurring at the pore scale, caused by the liquid/solid susceptibility contrast. Previously, we introduced a generic model for the diffusion exponent of the form −antek (where n is the number and te the temporal separation of spin echoes, and a is a composite diffusion parameter) in order to distinguish the influence of relaxation and diffusion in CPMG data. Here, we improve the analysis by introducing an automatic search for the optimum power k that best describes the diffusion behavior. This automated method is more efficient than the manual trial-and-error grid search adopted previously, and avoids variability through subjective judgments of experimentalists. Although our method does not avoid the inherent assumption that the diffusion exponent depends on a single k value, we show through simulation and experiment that it is robust in measurements of heterogeneous systems that violate this assumption. In this way, we obtain quantitative T2 distributions from complicated porous structures and demonstrate the analysis with examples of ceramics used for filtration and catalysis, and limestone of relevance to the construction and petroleum industries

  14. Understanding generalized inversions of nuclear magnetic resonance transverse relaxation time in porous media

    Energy Technology Data Exchange (ETDEWEB)

    Mitchell, J., E-mail: JMitchell16@slb.com [Schlumberger Gould Research, High Cross, Madingley Road, Cambridge CB3 0EL (United Kingdom); Chandrasekera, T. C. [Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge CB2 3RA (United Kingdom)

    2014-12-14

    The nuclear magnetic resonance transverse relaxation time T{sub 2}, measured using the Carr-Purcell-Meiboom-Gill (CPMG) experiment, is a powerful method for obtaining unique information on liquids confined in porous media. Furthermore, T{sub 2} provides structural information on the porous material itself and has many applications in petrophysics, biophysics, and chemical engineering. Robust interpretation of T{sub 2} distributions demands appropriate processing of the measured data since T{sub 2} is influenced by diffusion through magnetic field inhomogeneities occurring at the pore scale, caused by the liquid/solid susceptibility contrast. Previously, we introduced a generic model for the diffusion exponent of the form −ant{sub e}{sup k} (where n is the number and t{sub e} the temporal separation of spin echoes, and a is a composite diffusion parameter) in order to distinguish the influence of relaxation and diffusion in CPMG data. Here, we improve the analysis by introducing an automatic search for the optimum power k that best describes the diffusion behavior. This automated method is more efficient than the manual trial-and-error grid search adopted previously, and avoids variability through subjective judgments of experimentalists. Although our method does not avoid the inherent assumption that the diffusion exponent depends on a single k value, we show through simulation and experiment that it is robust in measurements of heterogeneous systems that violate this assumption. In this way, we obtain quantitative T{sub 2} distributions from complicated porous structures and demonstrate the analysis with examples of ceramics used for filtration and catalysis, and limestone of relevance to the construction and petroleum industries.

  15. Modification of chemical and physical factors in steamflood to increase heavy oil recovery

    Energy Technology Data Exchange (ETDEWEB)

    Yortsos, Y.C.

    1991-04-01

    Three aspects of vapor-liquid flow in porous media were addressed: (i) Extension of a previous vapor-liquid model for solution gas-drive to a water liquid-water vapor (steam) system in a pore network; (ii) Visualization of steam injection in Hele-Shaw cells and glass micromodels; and (iii) Macroscopic description of concurrent vapor-liquid flow in porous media. Significant progress was made in the study of reservoir heterogeneity and its effects on flow processes. The authors have considered three general areas: (i) The representation of naturally fractured systems; (ii) The large-scale averaging (derivation of pseudo-functions) for displacement in macroscopically heterogeneous systems; and (iii) The study of parallel flow, typically encountered in long and narrow reservoirs. The third area of research in this report involves chemical additives for the improvement of recovery efficiencies. The authors have been studying the following three aspects: (i) Caustic additives at elevated temperatures; (ii) Foam generation; and (iii) Non-Newtonian flow in porous media. The study of caustic injection at elevated temperatures, specifically the silica dissolution and caustic consumption, has been terminated. A technical report will summarize the results obtained. Here, the authors address the remaining aspects (ii) and (iii). 107 refs., 87 figs., 4 tabs.

  16. Experimental and Theoretical Investigations of Reaction-Coupled Flow and Transport in Porous Media

    Science.gov (United States)

    Kim, J.; Schwartz, F. W.

    2004-12-01

    In some systems, it is possible to observe complex patterns of coupling between fluid and flow and mass transport when reactions involving a solid phase are operative. For example, dissolution and precipitation reactions can change a porous medium's physical properties such as porosity and permeability. These changes influence fluid flow, which affect the concentration of dissolved solids, the composition of solid phases, and the rate and direction of advective transport. Both experimental and modeling studies were conducted to investigate the coupling between flow and transport due to effects of fluid density, dissolution/precipitation reactions, and heterogeneity in medium properties. The complex chemical system is created by pumping a dilute Fe(ClO4)3 solution through a medium created by mixing glass beads and crushed calcite. Fe3+ rapidly hydrolyzes to produce hydroxo complexes and H+. As pH increases through reaction with calcite, a poorly crystallized solid, ferric oxyhydroxide precipitates. Two-dimensional flow tank studies are use to verify a novel modeling approach. In the model, there is full coupling of flow and transport due to permeability changes from dissolution/precipitation reactions. Further, TOUGHREACT is used to study reaction-front dynamics, and how the aqueous phase concentrations depend upon this pattern of evolution. Both the experimental and theoretical results highlight the complexity of coupling in systems with heterogeneous reactions. The important implication of this study is that details of interactions between pore fluid and the porous medium need to be well characterized in order to predict the changing aqueous concentrations.

  17. Porous block nanofiber composite filters

    Energy Technology Data Exchange (ETDEWEB)

    Ginley, David S.; Curtis, Calvin J.; Miedaner, Alexander; Weiss, Alan J.; Paddock, Arnold

    2016-08-09

    Porous block nano-fiber composite (110), a filtration system (10) and methods of using the same are disclosed. An exemplary porous block nano-fiber composite (110) includes a porous block (100) having one or more pores (200). The porous block nano-fiber composite (110) also includes a plurality of inorganic nano-fibers (211) formed within at least one of the pores (200).

  18. Theory of porous media - past and present

    Energy Technology Data Exchange (ETDEWEB)

    Boer, R. de [Essen Univ. (Germany). Inst. fuer Mechanik

    1998-10-01

    Porous solids filled with liquid or gas play an important role in engineering, e.g., in material science, petroleum industry, chemical engineering, and soil mechanics as well as in biomechanics. Although porous media are of considerable practical significance the description of their mechanical and thermodynamical behavior has been unsatisfactory for a long time. The theory to describe the complex thermodynamical behavior of such saturated porous solids has come to certain well-founded conclusions only recently. It is the goal of this paper to show the historical development of the porous media theory, which already started in the eighteenth century, formed in some areas by polemic disputes and tragic events in the lifes of the scientists involved. Furthermore, the current state of the research into this subject is discussed, whereby the state of the development of the material independent basic equations and the constitutive theory is illustrated. For a certain class of models general theorems, such as minimum and maximum problems, are derived and the uniqueness of solutions of boundary value problems is proved. (orig.)

  19. Simple method to generate and fabricate stochastic porous scaffolds

    International Nuclear Information System (INIS)

    Considerable effort has been made to generate regular porous structures (RPSs) using function-based methods, although little effort has been made for constructing stochastic porous structures (SPSs) using the same methods. In this short communication, we propose a straightforward method for SPS construction that is simple in terms of methodology and the operations used. Using our method, we can obtain a SPS with functionally graded, heterogeneous and interconnected pores, target pore size and porosity distributions, which are useful for applications in tissue engineering. The resulting SPS models can be directly fabricated using additive manufacturing (AM) techniques. - Highlights: • Random porous structures are constructed based on their regular counterparts. • Functionally graded random pores can be constructed easily. • The scaffolds can be directly fabricated using additive manufacturing techniques

  20. A volume-balance model for flow on porous media

    Science.gov (United States)

    Malaga, Carlos; Mandujano, Francisco; Becerra, Julian

    2015-11-01

    Volume-balance models are used by petroleum engineers for simulating multiphase and multicomponent flow phenomena in porous media and the extraction process in oil reservoirs. In these models, mass conservation equations and Darcy's law are supplemented by a balance condition for the pore and fluid volumes. This provides a pressure equation suitable for simulating a compressible flow within a compressible solid matrix. Here we present an alternative interpretation of the volume-balance condition that includes the advective transport within a consolidated porous media. We obtain a modified equation for the time evolution of the pressure field. Numerical tests for phase separation under gravity are presented for multiphase three dimensional flow in heterogeneous porous media. The authors acknowledge funding from Fondo Sectorial CONACYT-SENER grant number 42536 (DGAJ-SPI-34-170412-217).

  1. Study of the radiolysis of water in porous media

    International Nuclear Information System (INIS)

    The understanding of the production of H2 in the radiolysis of water confined into pores of concrete is important for the disposal of radioactive waste. In order to describe the mechanisms of water radiolysis in such heterogeneous porous systems we have studied the behaviour under gamma radiation of water confined in porous silica glasses with pores going from 8 to 300 nm of diameter and meso-porous molecular sieves (MCM-41). The radiolytic yields of hydroxyl radicals, hydrated electron and dihydrogen, have been determined with respect to the pore size of materials. The increase of these radiolytic yields compared to those of free water allowed us to show a charge transfer from silica to confined water. On the other hand the kinetics of hydrated electron reactions measured by pulse radiolysis are not modified. (author)

  2. Simple method to generate and fabricate stochastic porous scaffolds

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Nan, E-mail: y79nzw@163.com; Gao, Lilan; Zhou, Kuntao

    2015-11-01

    Considerable effort has been made to generate regular porous structures (RPSs) using function-based methods, although little effort has been made for constructing stochastic porous structures (SPSs) using the same methods. In this short communication, we propose a straightforward method for SPS construction that is simple in terms of methodology and the operations used. Using our method, we can obtain a SPS with functionally graded, heterogeneous and interconnected pores, target pore size and porosity distributions, which are useful for applications in tissue engineering. The resulting SPS models can be directly fabricated using additive manufacturing (AM) techniques. - Highlights: • Random porous structures are constructed based on their regular counterparts. • Functionally graded random pores can be constructed easily. • The scaffolds can be directly fabricated using additive manufacturing techniques.

  3. Staggered-Grid Finite Difference Method with Variable-Order Accuracy for Porous Media

    OpenAIRE

    Jinghuai Gao; Yijie Zhang

    2013-01-01

    The numerical modeling of wave field in porous media generally requires more computation time than that of acoustic or elastic media. Usually used finite difference methods adopt finite difference operators with fixed-order accuracy to calculate space derivatives for a heterogeneous medium. A finite difference scheme with variable-order accuracy for acoustic wave equation has been proposed to reduce the computation time. In this paper, we develop this scheme for wave equations in porous media...

  4. Synthesis and optical properties of three-dimensional porous core-shell nanoarchitectures.

    Science.gov (United States)

    Qian, Li-Hua; Ding, Yi; Fujita, Takeshi; Chen, Ming-Wei

    2008-05-01

    Three-dimensional porous core-shell nanostructures consisting of gold skeletons and silver shells were fabricated by controllable electroless plating. Optical properties of the 3D nanocomposite with a heterogeneous interface exhibit a significant shell-thickness dependence. The porous core-shell structure with an optimized shell thickness of approximately 3-5 nm exhibits a considerable improvement in surface-enhanced Raman scattering. This study has important implications in the functionalization of nanoporous metals by surface modification. PMID:18355096

  5. Modification of chemical and physical factors in steamflood to increase heavy oil recovery. Annual report, October 1, 1992--September 30, 1993

    Energy Technology Data Exchange (ETDEWEB)

    Yortsos, Y.C.

    1994-10-01

    Thermal methods, and particularly steam injection, are currently recognized as the most promising for the efficient recovery of heavy oil. Despite significant progress, however, important technical issues remain open. Specifically, still inadequate is our knowledge of the complex interaction between porous media and the various fluids of thermal recovery (steam, water, heavy oil, gases, and chemicals). While, the interplay of heat transfer and fluid flow with pore- and macro-scale heterogeneity is largely unexplored. Objectives of this work contract are to carry out new studies in the following areas: displacement and flow properties of fluids involving phase change in porous media; flow properties of mobility control fluids (such as foam); and the effect of reservoir heterogeneity on thermal recovery. Specific projects address the need to improve heavy oil recovery from typical reservoirs as well as less conventional fractured reservoirs producing from vertical or horizontal wells. In the area of vapor-liquid flow, we present the continuation of work on the pore network modeling of bubble growth in porous media driven by the application of a prescribed heat flux or superheat. The scaling of bubble growth in porous media is also discussed. In another study we study the problem of steam injection in fractured systems using visualization in micromodels. The interplay of drainage, imbibition and bubble growth problems is discussed.

  6. Study on Porous Silicon with P-N Junction Sensor for Humidity Measurement

    Institute of Scientific and Technical Information of China (English)

    Chuzhe Tu; Zhenhong Jia

    2006-01-01

    Porous materials used for humidity sensing have been commercialized. In this paper, the preparation and humidity sensing characteristics of porous silicon with P-N junctions (PNJPS) are studied. PNJPS is made by electro-chemical anodic etched method from silicon wafers with P-N junctions. Its porous structure is verified by scanning electronic micrograph.Experiments also show that PNJPS has high sensitivity, short response time (less than 30 seconds), and long-term stability.

  7. Crystallization of amorphous silicon thin films deposited by PECVD on nickel-metalized porous silicon

    OpenAIRE

    Ben Slama, Sonia; Hajji, Messaoud; Ezzaouia, Hatem

    2012-01-01

    Porous silicon layers were elaborated by electrochemical etching of heavily doped p-type silicon substrates. Metallization of porous silicon was carried out by immersion of substrates in diluted aqueous solution of nickel. Amorphous silicon thin films were deposited by plasma-enhanced chemical vapor deposition on metalized porous layers. Deposited amorphous thin films were crystallized under vacuum at 750°C. Obtained results from structural, optical, and electrical characterizations show that...

  8. Plasma-deposited fluoropolymer film mask for local porous silicon formation

    OpenAIRE

    Defforge, Thomas; Capelle, Marie; Tran-Van, François; Gautier, Gaël

    2012-01-01

    The study of an innovative fluoropolymer masking layer for silicon anodization is proposed. Due to its high chemical resistance to hydrofluoric acid even under anodic bias, this thin film deposited by plasma has allowed the formation of deep porous silicon regions patterned on the silicon wafer. Unlike most of other masks, fluoropolymer removal after electrochemical etching is rapid and does not alter the porous layer. Local porous regions were thus fabricated both in p+-type and low-doped n-...

  9. Facile Synthesis of Porous Silicon Nanofibers by Magnesium Reduction for Application in Lithium Ion Batteries

    OpenAIRE

    Cho, Daehwan; Kim, Moonkyoung; Hwang, Jeonghyun; Park, Jay Hoon; Joo, Yong Lak; Jeong, Youngjin

    2015-01-01

    We report a facile fabrication of porous silicon nanofibers by a simple three-stage procedure. Polymer/silicon precursor composite nanofibers are first fabricated by electrospinning, a water-based spinning dope, which undergoes subsequent heat treatment and then reduction using magnesium to be converted into porous silicon nanofibers. The porous silicon nanofibers are coated with a graphene by using a plasma-enhanced chemical vapor deposition for use as an anode material of lithium ion batter...

  10. Mass Transfer and Porous Media (MTPM)

    Energy Technology Data Exchange (ETDEWEB)

    Rotenberg, B.; Marry, V.; Malikova, N.; Vuilleumier, R.; Giffaut, E.; Turq, P.; Robinet, J.C.; Diaz, N.; Sardini, P.; Goutelard, F.; Menut, D.; Parneix, J.C.; Sammartino, S.; Pret, D.; Coelho, D.; Jougnot, D.; Revil, A.; Boulin, P.F.; Angulo-Jaramillo, R.; Daian, J.F.; Talandier, J.; Berne, P.; Cochepin, B.; Trotignon, L.; Bildstein, O.; Steefel, C.; Lagneau, V.; Van der Lee, J.; Birchall, D.J.; Harrington, J.F.; Noy, D.J.; Sellin, P.; Bildstein, O.; Piault, E.; Trotignon, L.; Montarnal, P.; Deville, E.; Genty, A.; Le Potier, C.; Imbert, C.; Semete, P.; Desgree, P.; Fevrier, B.; Courtois, A.; Touze, G.; Sboui, A.; Roberts, J.E.; Jaffre, J.; Glaus, M.A.; Rosse, R.; Van Loon, L.R.; Matray, J.M.; Parneix, J.C.; Tinseau, E.; Pret, D.; Mayor, J.C.; Ohkubo, T.; Kikuchi, H.; Yamaguchi, M.; Alonso, U.; Missana, T.; Garcia-Gutierrez, M.; Patelli, A.; Siitari-Kauppi, M.; Leskinen, A.; Rigato, V.; Samper, J.; Dewonck, S.; Zheng, L.; Yang, Q.; Naves, A.; Dai, Z.; Samper, J.; Wolfsberg, A.; Levitt, D.; Cormenzana, J.L.; Missana, T.; Mingarro, M.; Schampera, B.; Dultz, S.; Riebe, B.; Samper, J.; Yang, Q.; Genty, A.; Perraud, D.; Poller, A.; Mayer, G.; Croise, J.; Marschall, P.; Krooss, B.; Matray, J.M.; Tanaka, T.; Vogel, P.; Lavanchy, J.M.; Enssle, C.P.; Cruchaudet, M.; Dewonck, S.; Descostes, M.; Blin, V.; Radwan, J.; Poinssot, C.; Mibus, J.; Sachs, S.; Devol-Brown, I.; Motellier, S.; Tinseau, E.; Thoby, D.; Marsal, F.; DeWindt, L.; Tinseau, E.; Pellegrini, D.; Bauer, A.; Fiehn, B.; Marquardt, Ch.; Romer, J.; Gortzen, A.; Kienzler, B

    2007-07-01

    This session gathers 48 articles (posters) dealing with: interlayer / micro-pore exchange of water and ions in clays: a molecular dynamics study; the multi-scale characterisation of mineral and textural spatial heterogeneities in Callovo-Oxfordian argilite and its consequence on solute species diffusion modelling; the diffusion of ions in unsaturated clay rocks: Theory and application to the Callovo- Oxfordian argillite; the porous media characterization with respect to gas transfer in Callovo Oxfordian argillite; the predictions on a 2-D cementation experiment in porous medium: intercomparison on the Comedie project; the large-scale gas injection test (LASGIT) at the Aespoe hard rock laboratory in Sweden; simulating the geochemical coupling between vitrified waste, canister and near-field on the alliances platform; toward radionuclide transport calculations on whole radioactive waste disposal with CAST3M platform; the experimental study of the water permeability of a partially saturated argillite; a mixed hexahedral finite elements for Darcy flow calculation in clay porous media; the diffusive properties of stainless steel filter discs before and after use in diffusion experiments with compacted clays; the structural organization of porosity in the Opalinus clay at the Mont Terri Rock Laboratory under saturated and unsaturated conditions; the evaluation of pore structure in compacted saturated Bentonite using NMR relaxometry; diffusion coefficients measurement in consolidated clays: a combination of micro-scale profiling and solid pore structure analyses; the numerical interpretation of in-situ DIR diffusion experiments on the Callovo- Oxfordian clay at the Meuse/Haute-Marne URL the identification of relative conductivity models for water flow and solute transport in unsaturated compacted Bentonite; diffusion experiments in Callovo- Oxfordian clay from the Meuse/Haute-Marne URL, France: experimental setup and data analyses; the transport in organo

  11. Mass Transfer and Porous Media (MTPM)

    International Nuclear Information System (INIS)

    This session gathers 48 articles (posters) dealing with: interlayer / micro-pore exchange of water and ions in clays: a molecular dynamics study; the multi-scale characterisation of mineral and textural spatial heterogeneities in Callovo-Oxfordian argilite and its consequence on solute species diffusion modelling; the diffusion of ions in unsaturated clay rocks: Theory and application to the Callovo- Oxfordian argillite; the porous media characterization with respect to gas transfer in Callovo Oxfordian argillite; the predictions on a 2-D cementation experiment in porous medium: intercomparison on the Comedie project; the large-scale gas injection test (LASGIT) at the Aespoe hard rock laboratory in Sweden; simulating the geochemical coupling between vitrified waste, canister and near-field on the alliances platform; toward radionuclide transport calculations on whole radioactive waste disposal with CAST3M platform; the experimental study of the water permeability of a partially saturated argillite; a mixed hexahedral finite elements for Darcy flow calculation in clay porous media; the diffusive properties of stainless steel filter discs before and after use in diffusion experiments with compacted clays; the structural organization of porosity in the Opalinus clay at the Mont Terri Rock Laboratory under saturated and unsaturated conditions; the evaluation of pore structure in compacted saturated Bentonite using NMR relaxometry; diffusion coefficients measurement in consolidated clays: a combination of micro-scale profiling and solid pore structure analyses; the numerical interpretation of in-situ DIR diffusion experiments on the Callovo- Oxfordian clay at the Meuse/Haute-Marne URL the identification of relative conductivity models for water flow and solute transport in unsaturated compacted Bentonite; diffusion experiments in Callovo- Oxfordian clay from the Meuse/Haute-Marne URL, France: experimental setup and data analyses; the transport in organo

  12. POROUS DIKE INTAKE EVALUATION

    Science.gov (United States)

    The report gives results of an evaluation of a porous dike intake. A small-scale test facility was constructed and continuously operated for 2 years under field conditions. Two stone dikes of gabion construction were tested: one consisted of 7.5 cm stones; and the other, 20 cm st...

  13. Hydrophobic, Porous Battery Boxes

    Science.gov (United States)

    Bragg, Bobby J.; Casey, John E., Jr.

    1995-01-01

    Boxes made of porous, hydrophobic polymers developed to contain aqueous potassium hydroxide electrolyte solutions of zinc/air batteries while allowing air to diffuse in as needed for operation. Used on other types of batteries for in-cabin use in which electrolytes aqueous and from which gases generated during operation must be vented without allowing electrolytes to leak out.

  14. Porous polyethylene and proplast

    OpenAIRE

    Berghaus, Alexander; Mulch, G.; Handrock, M

    1984-01-01

    A comparative animal study showed that, after implantation in skull defects in guinea pigs, porous high-density polyethylene (PHDPE) was substantially better anchored in the bone than Proplast, and had greater stability of form and structure. In Proplast, ingrowth of fibrous tissue caused partial structural dilatation and fragmentation, which could limit its suitability for use in reconstructive surgery.

  15. Nuclear magnetic relaxation of liquids in porous media

    International Nuclear Information System (INIS)

    Nuclear magnetic relaxation is useful for probing physical and chemical properties of liquids in porous media. Examples are given on high surface area porous materials including calibrated porous silica glasses, granular packings, plaster pastes, cement-based materials and natural porous materials, such as sandstone and carbonate rocks. Here, we outline our recent NMR relaxation work for these very different porous materials. For instance, low field NMR relaxation of water in calibrated granular packings leads to striking different pore-size dependencies of the relaxation times T1 and T2 when changing the amount of surface paramagnetic impurities. This allows separation of the diffusion and surface limited regimes of relaxation in these macroporous media. The magnetic field dependence of the nuclear spin-lattice relaxation rate 1/T1(ω0) is also a rich source of dynamical information for characterizing the molecular dynamics of liquids in porous media. This allows a continuous characterization of the evolving microstructure of various cementitious materials. Our recent applications of two-dimensional (2D) T1-T2 and T2-z-store-T2 correlation experiments have evidenced the water exchange in connected micropores of cement pastes. The direct probing of water adsorption time on a solid surface gives access to an original characterization of the surface nano-wettability of porous plaster pastes. We show that such a parameter depends directly on the physical chemistry of the pore surfaces. Lastly, we outline our recent measurements of wettability in oil/brine/reservoir carbonate rocks.

  16. Adsorption of lead at variable pH onto a natural porous medium: Modeling of batch and column experiments

    Energy Technology Data Exchange (ETDEWEB)

    Papini, M.P.; Kahie, Y.D.; Troia, B.; Majone, M.

    1999-12-15

    The surface complexation approach has been applied to describe the adsorption of lead and proton onto a heterogeneous natural porous medium at constant ionic strength. Acid-base titration experiments were used to determine the minimum number of sites needed to describe the surface heterogeneity. Lead adsorption tests at several pH and total lead concentration were used to complete the model structure, whose adjustable parameters (site concentration and apparent formation constants) were determined by nonlinear multivariate regression of titration and adsorption data. The final model represents the acid-base properties of the surface by the presence of two amphoteric sites, SOH and TOH, and a monoprotic one, MOH; whereas lead adsorption is considered only onto SOH and MOH sites. The model allows a good representation of the experimental behavior in the whole experimental range. Theoretical surface speciation shows that lead adsorption occurs mostly onto site MOH at low pH level and on both SOH and MOH sites at higher values. The model was independently validated by simulating Pb and pH breakthrough experiments performed in small chromatographic columns. Experimental breakthroughs are well predicted by an advection-dispersion transport model coupled with the chemical equilibrium routine (IMPACT), without any parameter adjustment. A large spreading of Pb and pH breakthroughs was calculated and experimentally observed, even in the absence of any kinetic effect. That spreading is explained in terms of the concomitant presence of competitive adsorption and surface heterogeneity.

  17. The multiphase flow and heat transfer in porous media

    OpenAIRE

    Starikovicius, V.

    2003-01-01

    In first part of this work, summaries of traditional Multiphase Flow Model and more recent Multiphase Mixture Model are presented. Attention is being paid to attempts include various heterogeneous aspects into models. In second part, MMM based differential model for two-phase immiscible flow in porous media is considered. A numerical scheme based on the sequential solution procedure and control volume based finite difference schemes for the pressure and saturation-conservation equations is de...

  18. Fabrication of interfacial functionalized porous polymer monolith and its adsorption properties of copper ions

    Energy Technology Data Exchange (ETDEWEB)

    Han, Jiaxi; Du, Zhongjie; Zou, Wei; Li, Hangquan; Zhang, Chen, E-mail: zhangch@mail.buct.edu.cn

    2014-07-15

    Highlights: • Interface functionalized PGMA porous monolith was fabricated. • The adsorption capacity of Cu{sup 2+} was 35.3 mg/g. • The effects of porous structure on the adsorption of Cu{sup 2+} were studied. • The adsorption behaviors of porous monolith were studied. - Abstract: The interfacial functionalized poly (glycidyl methacrylate) (PGMA) porous monolith was fabricated and applied as a novel porous adsorbent for copper ions (Cu{sup 2+}). PGMA porous material with highly interconnected pore network was prepared by concentrated emulsion polymerization template. Then polyacrylic acid (PAA) was grafted onto the interface of the porous monolith by the reaction between the epoxy group on PGMA and a carboxyl group on PAA. Finally, the porous monolith was interfacial functionalized by rich amount of carboxyl groups and could adsorb copper ions effectively. The chemical structure and porous morphology of the porous monolith were measured by Fourier transform infrared spectroscopy and scanning electron microscopy. Moreover, the effects of pore size distribution, pH value, co-existing ions, contacting time, and initial concentrations of copper ions on the adsorption capacity of the porous adsorbents were studied.

  19. Controlled synthesis of porous platinum nanostructures for catalytic applications.

    Science.gov (United States)

    Cao, Yanqin; Zhang, Junwei; Yang, Yong; Huang, Zhengren; Long, Nguyen Viet; Nogami, Masayuki

    2014-02-01

    Porous platinum, that has outstanding catalytic and electrical properties and superior resistant characteristics to corrosion, has been widely applied in chemical, petrochemical, pharmaceutical, electronic, and automotive industries. As the catalytic activity and selectivity depend on the size, shape and structure of nanomaterials, the strategies for controlling these factors of platinum nanomaterials to get excellent catalytic properties are discussed. Here, recent advances in the design and preparation of various porous platinum nanostructures are reviewed, including wet-chemical synthesis, electro-deposition, galvanic replacement reaction and de-alloying technology. The applications of various platinum nanostructures are also discussed, especially in fuel cells. PMID:24749422

  20. A Mechanochemical Approach to Porous Silicon Nanoparticles Fabrication

    Directory of Open Access Journals (Sweden)

    Luca De Stefano

    2011-06-01

    Full Text Available Porous silicon samples have been reduced in nanometric particles by a well known industrial mechanical process, the ball grinding in a planetary mill; the process has been extended to crystalline silicon for comparison purposes. The silicon nanoparticles have been studied by X-ray diffraction, infrared spectroscopy, gas porosimetry and transmission electron microscopy. We have estimated crystallites size from about 50 nm for silicon to 12 nm for porous silicon. The specific surface area of the powders analyzed ranges between 100 m2/g to 29 m2/g depending on the milling time, ranging from 1 to 20 h. Electron microscopy confirms the nanometric size of the particles and reveals a porous structure in the powders obtained by porous silicon samples which has been preserved by the fabrication conditions. Chemical functionalization during the milling process by a siloxane compound has also been demonstrated.

  1. Final Report - Montana State University - Microbial Activity and Precipitation at Solution-Solution Mixing Zones in Porous Media

    Energy Technology Data Exchange (ETDEWEB)

    Gerlach, Robin [Montana State University

    2014-10-31

    Background. The use of biological and chemical processes that degrade or immobilize contaminants in subsurface environments is a cornerstone of remediation technology. The enhancement of biological and chemical processes in situ, involves the transport, displacement, distribution and mixing of one or more reactive agents. Biological and chemical reactions all require diffusive transport of solutes to reaction sites at the molecular scale and accordingly, the success of processes at the meter-scale and larger is dictated by the success of phenomena that occur at the micron-scale. However, current understanding of scaling effects on the mixing and delivery of nutrients in biogeochemically dynamic porous media systems is limited, despite the limitations this imposes on the efficiency and effectiveness of the remediation challenges at hand. Objectives. We therefore proposed to experimentally characterize and computationally describe the growth, evolution, and distribution of microbial activity and mineral formation as well as changes in transport processes in porous media that receive two or more reactive amendments. The model system chosen for this project was based on a method for immobilizing 90Sr, which involves stimulating microbial urea hydrolysis with ensuing mineral precipitation (CaCO3), and co-precipitation of Sr. Studies at different laboratory scales were used to visualize and quantitatively describe the spatial relationships between amendment transport and consumption that stimulate the production of biomass and mineral phases that subsequently modify the permeability and heterogeneity of porous media. Biomass growth, activity, and mass deposition in mixing zones was investigated using two-dimensional micro-model flow cells as well as flow cells that could be analyzed using synchrotron-based x-ray tomography. Larger-scale flow-cell experiments were conducted where the spatial distribution of media properties, flow, segregation of biological activity and

  2. Hydrogen storage by physisorption on porous materials

    Energy Technology Data Exchange (ETDEWEB)

    Panella, B.

    2006-09-13

    A great challenge for commercializing hydrogen powered vehicles is on-board hydrogen storage using economic and secure systems. A possible solution is hydrogen storage in light-weight solid materials. Here three principle storage mechanisms can be distinguished: i) absorption of hydrogen in metals ii) formation of compounds with ionic character, like complex hydrides and iii) physisorption (or physical adsorption) of hydrogen molecules on porous materials. Physical adsorption exhibits several advantages over chemical hydrogen storage as for example the complete reversibility and the fast kinetics. Two classes of porous materials were investigated for physical hydrogen storage, i.e. different carbon nanostructures and crystalline metal-organic frameworks possessing extremely high specific surface area. Hydrogen adsorption isotherms were measured using a Sieverts' apparatus both at room temperature and at 77 K at pressures up to the saturation regime. Additionally, the adsorption sites of hydrogen in these porous materials were identified using thermal desorption spectroscopy extended to very low temperatures (down to 20 K). Furthermore, the adsorbed hydrogen phase was studied in various materials using Raman spectroscopy at different pressures and temperatures. The results show that the maximum hydrogen storage capacity of porous materials correlates linearly with the specific surface area and is independent of structure and composition. In addition the pore structure of the adsorbent plays an important role for hydrogen storage since the adsorption sites for H2 could be assigned to pores possessing different dimensions. Accordingly it was shown that small pores are necessary to reach high storage capacities already at low pressures. This new understanding may help to tailor and optimize new porous materials for hydrogen storage. (orig.)

  3. Heterogeneous Social Preferences

    OpenAIRE

    Erlei, Mathias

    2003-01-01

    Recent research has shown the usefulness of social preferences for explaining behavior in laboratory experiments. This paper demonstrates that models of social preferences are particularly powerful in explaining behavior if they are embedded in a setting of heteroge-neous actors with heterogeneous (social) preferences. For this purpose a simple model is in-troduced that combines the basic ideas of inequity aversion, social welfare preferences, recip-rocity and heterogeneity. This model is app...

  4. Heterogeneous Chemistry in Global Chemistry Transport Models

    Science.gov (United States)

    Stadtler, Scarlet; Simpson, David; Schultz, Martin; Bott, Andreas

    2016-04-01

    The impact of six tropospheric heterogeneous reactions on ozone and nitrogen species was studied using two chemical transport models EMEP MSC-W and ECHAM6-HAMMOZ. Since heterogeneous reactions depend on reactant concentrations (in this study these are N_2O_5, NO_3, NO_2, O_3, HNO_3, HO_2) and aerosol surface area S_a, the modeled surface area of both models was compared to a satellite product retrieving the surface area. This comparison shows a good agreement in global pattern and especially the capability of both models to capture the extreme aerosol loadings in East Asia. Further, the impact of the heterogeneous reactions was evaluated by the simulation of a reference run containing all heterogeneous reactions and several sensitivity runs. One reaction was turned off in each sensitivity run to compare it with the reference run. As previously shown, the analysis of the sensitivity runs shows that the globally most important heterogeneous reaction is the one of N_2O_5. Nevertheless, NO_2, NO_3, HNO3 and HO2 heterogeneous reactions gain relevance particular in East China due to presence of high NOx concentrations and high Sa in the same region. The heterogeneous reaction of O3 itself on dust is compared to the other heterogeneous reactions of minor relevance. Evaluation of the models with northern hemispheric ozone surface observations yields a better agreement of the models with observations when the heterogeneous reactions are incorporated. Impacts of emission changes on the importance of the heterogeneous chemistry will be discussed.

  5. Hydrodynamic dispersion within porous biofilms

    KAUST Repository

    Davit, Y.

    2013-01-23

    Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behavior by controlling nutrient supply, evacuation of waste products, and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilm-scale in the case where the width of the channels is significantly smaller than the thickness of the biofilm. We show that solute transport may be described via two coupled partial differential equations or telegrapher\\'s equations for the averaged concentrations. These models are particularly relevant for chemicals, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterized by a second-order tensor whose components depend on (1) the topology of the channels\\' network; (2) the solute\\'s diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion dominated, this analysis shows that hydrodynamic dispersion effects may significantly contribute to transport. © 2013 American Physical Society.

  6. Simulation of Tracer Transport in Porous Media: Application to Bentonites; Simulacion del Transporte de Trazadores en Medios Porosos: Aplicacion al Caso de Arcillas

    Energy Technology Data Exchange (ETDEWEB)

    Bru, A.; Casero, D. [CIEMAT, Madrid (Spain)

    2001-07-01

    We present a formal framework to describe tracer transport in heterogeneous media, such as porous media like bentonites. In these media, mean field approximation is not valid because there exist some geometrical constraints and the transport is anomalous. (Author)

  7. Porous Organic Polymers for CO2 Capture

    KAUST Repository

    Teng, Baiyang

    2013-05-01

    Carbon dioxide (CO2) has long been regarded as the major greenhouse gas, which leads to numerous negative effects on global environment. The capture and separation of CO2 by selective adsorption using porous materials proves to be an effective way to reduce the emission of CO2 to atmosphere. Porous organic polymers (POPs) are promising candidates for this application due to their readily tunable textual properties and surface functionalities. The objective of this thesis work is to develop new POPs with high CO2 adsorption capacities and CO2/N2 selectivities for post-combustion effluent (e.g. flue gas) treatment. We will also exploit the correlation between the CO2 capture performance of POPs and their textual properties/functionalities. Chapters Two focuses on the study of a group of porous phenolic-aldehyde polymers (PPAPs) synthesized by a catalyst-free method, the CO2 capture capacities of these PPAPs exceed 2.0 mmol/g at 298 K and 1 bar, while keeping CO2/N2 selectivity of more than 30 at the same time. Chapter Three reports the gas adsorption results of different hyper-cross-linked polymers (HCPs), which indicate that heterocyclo aromatic monomers can greatly enhance polymers’ CO2/N2 selectivities, and the N-H bond is proved to the active CO2 adsorption center in the N-contained (e.g. pyrrole) HCPs, which possess the highest selectivities of more than 40 at 273 K when compared with other HCPs. Chapter Four emphasizes on the chemical modification of a new designed polymer of intrinsic microporosity (PIM) with high CO2/N2 selectivity (50 at 273 K), whose experimental repeatability and chemical stability prove excellent. In Chapter Five, we demonstrate an improvement of both CO2 capture capacity and CO2/N2 selectivity by doping alkali metal ions into azo-polymers, which leads a promising method to the design of new porous organic polymers.

  8. Strong, Lightweight, Porous Materials

    Science.gov (United States)

    Leventis, Nicholas; Meador, Mary Ann B.; Johnston, James C.; Fabrizio, Eve F.; Ilhan, Ulvi

    2007-01-01

    A new class of strong, lightweight, porous materials has been invented as an outgrowth of an effort to develop reinforced silica aerogels. The new material, called X-Aerogel is less hygroscopic, but no less porous and of similar density to the corresponding unmodified aerogels. However, the property that sets X-Aerogels apart is their mechanical strength, which can be as much as two and a half orders of magnitude stronger that the unmodified aerogels. X-Aerogels are envisioned to be useful for making extremely lightweight, thermally insulating, structural components, but they may also have applications as electrical insulators, components of laminates, catalyst supports, templates for electrode materials, fuel-cell components, and filter membranes.

  9. Electrochemically Formed Porous Silica

    Directory of Open Access Journals (Sweden)

    Jean-Noël Chazalviel

    2011-04-01

    Full Text Available Controlled electrochemical formation of porous silica can be realized in dilute aqueous, neutral-pH, fluoride medium. Formation of a porous film is initiated by sweeping the potential applied to silicon to values higher than 20 V. Film formation, reaching a steady state, may be pursued in a wide range of potentials, including lower potentials. The origin of a threshold potential for porous film initiation has been explained quantitatively. All of the films appear mesoporous. Films grown at high potentials exhibit a variety of macrostructures superimposed on the mesoporosity. These macrostructures result from selective dissolution of silica induced by local pH lowering due to oxygen evolution. Films grown at potentials lower than 15 V appear uniform on the micrometer scale. However, all of the films also exhibit a stratified structure on the scale of a few tens of nanometres. This periodic structure can be traced back to the oscillatory behavior observed during the electrochemical dissolution of silicon in fluoride medium. It suggests that periodic breaking of the growing film may be responsible for this morphology.

  10. Heterogeneous network architectures

    DEFF Research Database (Denmark)

    Christiansen, Henrik Lehrmann

    2006-01-01

    Future networks will be heterogeneous! Due to the sheer size of networks (e.g., the Internet) upgrades cannot be instantaneous and thus heterogeneity appears. This means that instead of trying to find the olution, networks hould be designed as being heterogeneous. One of the key equirements here...... is flexibility. This thesis investigates such heterogeneous network architectures and how to make them flexible. A survey of algorithms for network design is presented, and it is described how using heuristics can increase the speed. A hierarchical, MPLS based network architecture is described...... and it is discussed that it is advantageous to heterogeneous networks and illustrated by a number of examples. Modeling and simulation is a well-known way of doing performance evaluation. An approach to event-driven simulation of communication networks is presented and mixed complexity modeling, which can simplify...

  11. Synthesis and characterization of nanostructured Ag on porous titania

    International Nuclear Information System (INIS)

    In this work, porous titania was prepared on bulk Ti by chemical oxidation, and then nanostructured silver (Ag) was deposited on titania surface by ion beam sputtering. After annealing treatment, Ag/TiO2 composites were characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results indicated that a nano-porous titania layer with mean pore size of 150 nm and thickness of 1 μm was formed by chemical oxidation at 80 deg. C for 45 min. There were three Ag species (Ag (0), Ag (1+), and Ag (2+)) on composites surface after annealing treatment, and metallic Ag content achieved maximum value with annealing temperature of 500 deg. C in air. Ag showed high thermal stability being partly attributed to the inhibiting the diffusion of Ag by the underlying porous titania.

  12. Buried Porous Silicon-Germanium Layers in Monocrystalline Silicon Lattices

    Science.gov (United States)

    Fathauer, Robert W. (Inventor); George, Thomas (Inventor); Jones, Eric W. (Inventor)

    1998-01-01

    Monocrystalline semiconductor lattices with a buried porous semiconductor layer having different chemical composition is discussed and monocrystalline semiconductor superlattices with a buried porous semiconductor layers having different chemical composition than that of its monocrystalline semiconductor superlattice are discussed. Lattices of alternating layers of monocrystalline silicon and porous silicon-germanium have been produced. These single crystal lattices have been fabricated by epitaxial growth of Si and Si-Ge layers followed by patterning into mesa structures. The mesa structures are strain etched resulting in porosification of the Si-Ge layers with a minor amount of porosification of the monocrystalline Si layers. Thicker Si-Ge layers produced in a similar manner emitted visible light at room temperature.

  13. Functionalization control of porous silicon optical structures using reflectance spectra modeling for biosensing applications

    International Nuclear Information System (INIS)

    Highlights: → Porous silicon layers with sufficient adjusted pore size and defined porosity. → Biological molecules covalently attached on the modified porous silica surface. → Adjustment of experimental and calculated reflectance spectra to determine volume fraction of biomolecules in functionalized porous silicon structures: single layers and microcavity structures. - Abstract: Modeling and experimental reflectance spectra of porous silicon single layers at different steps of functionalization and protein grafting process are adjusted in order to determine the volume fraction of the biomolecules attached to the internal pore surface. This method is applied in order to control the efficiency of the chemical functionalization process of porous silicon single layers. Using results from single porous silicon layer study, theoretical microcavity is simulated at each step of the functionalization process. The calculated reflectance spectrum is in good agreement to the experimental one. Therefore the single layers study can be applied to multilayer structures and can be adapted for other optical structures such as waveguides, interferometers for biosensing applications.

  14. Nitrogen-rich porous adsorbents for CO2 capture and storage.

    Science.gov (United States)

    Li, Pei-Zhou; Zhao, Yanli

    2013-08-01

    The construction of physical or chemical adsorbents for CO2 capture and sequestration (CCS) is a vital technology in the interim period on the way towards a sustainable low-carbon future. The search for efficient materials to satisfy the increasing demand for CCS has become extremely important. Porous materials, including porous silica, porous carbons, and newly developed metal-organic frameworks and porous organic polymers, possessing regular and well-defined porous geometry and having a high surface area and pore volume, have been widely studied for separations on laboratory scale. On account of the dipole-quadrupole interactions between the polarizable CO2 molecule and the accessible nitrogen site, the investigations have indicated that the incorporation of accessible nitrogen-donor groups into the pore walls of porous materials can improve the affinity to CO2 and increase the CO2 uptake capacity and selectivity. The CO2 -adsorption process based on solid nitrogen-rich porous adsorbents does generally not require heating of a large amount of water (60-70 wt%) for regeneration, while such a heating approach cannot be avoided in the regeneration of amine-based solution absorption processes. Thus, nitrogen-rich porous adsorbents show good regeneration properties without sacrificing high separation efficiency. As such, nitrogen-rich porous materials as highly promising CO2 adsorbents have been broadly fabricated and intensively investigated. This Focus Review highlights recent significant advances in nitrogen-rich porous materials for CCS. PMID:23744799

  15. Selective formation of porous silicon

    Science.gov (United States)

    Fathauer, Robert W. (Inventor); Jones, Eric W. (Inventor)

    1993-01-01

    A pattern of porous silicon is produced in the surface of a silicon substrate by forming a pattern of crystal defects in said surface, preferably by applying an ion milling beam through openings in a photoresist layer to the surface, and then exposing said surface to a stain etchant, such as HF:HNO3:H2O. The defected crystal will preferentially etch to form a pattern of porous silicon. When the amorphous content of the porous silicon exceeds 70 percent, the porous silicon pattern emits visible light at room temperature.

  16. Graphene: A Promising Two-Dimensional Support for Heterogeneous Catalysts

    OpenAIRE

    Fan, Xiaobin

    2015-01-01

    Graphene has many advantages that make it an attractive two-dimensional (2D) support for heterogeneous catalysts. It not only allows the high loading of targeted catalytic species but also facilitates the mass transfer during the reaction processes. These advantages, along with its unique physical and chemical properties, endow graphene great potential as catalyst support in heterogeneous catalysis.

  17. Multifunctional porous solids derived from tannins

    Science.gov (United States)

    Celzard, Alain; Fierro, Vanessa; Pizzi, Antonio; Zhao, Weigang

    2013-03-01

    Tannins are extremely valuable, non toxic, wood extractives combining reactivity towards aldehydes, low cost, natural origin and easy handling. When polymerized in the presence of suitable chemicals including blowing agent, ultra lightweight rigid tannin-based foams are obtained. If pyrolyzed under inert gas, reticulated carbon foams having the same pore structure and the same density are obtained. The most remarkable features of tannin-based foams are the following: mechanical resistance similar to, or higher than, that of commercial phenolic foams, tuneable pore size and permeability, infusibility, very low thermal conductivity, cheapness, ecological character, high resistance to flame and to chemicals. Carbon foams have even better properties and are also electrically conducting. Consequently, various applications are suggested for organic foams: cores of sandwich composite panels, sound and shock absorbers and thermal insulators, whereas carbon foams can be used as porous electrodes, filters for molten metals and corrosive chemicals, catalyst supports and adsorbents.

  18. Multifunctional porous solids derived from tannins

    International Nuclear Information System (INIS)

    Tannins are extremely valuable, non toxic, wood extractives combining reactivity towards aldehydes, low cost, natural origin and easy handling. When polymerized in the presence of suitable chemicals including blowing agent, ultra lightweight rigid tannin-based foams are obtained. If pyrolyzed under inert gas, reticulated carbon foams having the same pore structure and the same density are obtained. The most remarkable features of tannin-based foams are the following: mechanical resistance similar to, or higher than, that of commercial phenolic foams, tuneable pore size and permeability, infusibility, very low thermal conductivity, cheapness, ecological character, high resistance to flame and to chemicals. Carbon foams have even better properties and are also electrically conducting. Consequently, various applications are suggested for organic foams: cores of sandwich composite panels, sound and shock absorbers and thermal insulators, whereas carbon foams can be used as porous electrodes, filters for molten metals and corrosive chemicals, catalyst supports and adsorbents.

  19. Synthesis and characterization of a novel porous titanium silicate/g-C3N4 hybrid nanocomposite catalyst for environmental applications

    Science.gov (United States)

    Adepu, Ajay Kumar; Narayanan, Venkatathri

    2016-04-01

    Herein we developed a novel porous Titanium silicate/g-C3N4 (TSCN) hybrid composite with a inorganic-organic heterojunction. The synthesized porous TSCN were well characterized by various analytical techniques for structural and chemical properties evaluation. FESEM results shows the growth of finely distributed porous titanium silicate on the surface of the g-C3N4. Porous TSCN hybrid nanocomposite has a great influence on the electronic and optical properties.

  20. Strategy for Predicting Effective Transport Properties of Complex Porous Structures

    Czech Academy of Sciences Publication Activity Database

    Salejová, G.; Grof, Z.; Šolcová, Olga; Schneider, Petr; Kosek, J.

    2011-01-01

    Roč. 35, č. 2 (2011), s. 200-211. ISSN 0098-1354 Institutional research plan: CEZ:AV0Z40720504 Keywords : porous media * pore space reconstruction * effective diffusivity Subject RIV: CI - Industrial Chemistry, Chemical Engineering Impact factor: 2.320, year: 2011

  1. Coupled Flow and Reactivity in the Variably Saturated Porous Media

    Energy Technology Data Exchange (ETDEWEB)

    Palmer, Carl; Smith Bob W.

    2003-06-01

    This Environmental Management Science Program project (86598) is a collaborative effort between the University of Idaho (UI) and the Idaho National Engineering and Environmental Laboratory (INEEL) with the goal of developing a better understanding of the relationships between chemical reactivity, moisture content, and reactive transport for vadose zone porous media.

  2. Heterogeneous cellular networks

    CERN Document Server

    Hu, Rose Qingyang

    2013-01-01

    A timely publication providing coverage of radio resource management, mobility management and standardization in heterogeneous cellular networks The topic of heterogeneous cellular networks has gained momentum in industry and the research community, attracting the attention of standardization bodies such as 3GPP LTE and IEEE 802.16j, whose objectives are looking into increasing the capacity and coverage of the cellular networks. This book focuses on recent progresses,  covering the related topics including scenarios of heterogeneous network deployment, interference management i

  3. High-density oxidized porous silicon

    International Nuclear Information System (INIS)

    We have studied oxidized porous silicon (OPS) properties using Fourier transform infraRed (FTIR) spectroscopy and capacitance–voltage C–V measurements. We report the first experimental determination of the optimum porosity allowing the elaboration of high-density OPS insulators. This is an important contribution to the research of thick integrated electrical insulators on porous silicon based on an optimized process ensuring dielectric quality (complete oxidation) and mechanical and chemical reliability (no residual pores or silicon crystallites). Through the measurement of the refractive indexes of the porous silicon (PS) layer before and after oxidation, one can determine the structural composition of the OPS material in silicon, air and silica. We have experimentally demonstrated that a porosity approaching 56% of the as-prepared PS layer is required to ensure a complete oxidation of PS without residual silicon crystallites and with minimum porosity. The effective dielectric constant values of OPS materials determined from capacitance–voltage C–V measurements are discussed and compared to FTIR results predictions. (paper)

  4. Inverse opal ceria–zirconia: architectural engineering for heterogeneous catalysis

    OpenAIRE

    Umeda, G. A.; Chueh, William C.; Noailles, Liam; Haile, Sossina M.; Dunn, B. S.

    2008-01-01

    The application of inverse opal structured materials is extended to the ceria–zirconia (Ce_(0.5)Zr_(0.5)O_2) system and the significance of material architecture on heterogeneous catalysis, specifically, chemical oxidation, is examined.

  5. Tuning surface chemistry and nanostructure in porous silicon for molecular separation, detection and delivery /

    OpenAIRE

    Wu, Chia-Chen

    2013-01-01

    Mesoporous materials with engineered surface properties are of interest for molecular separations, catalysis, drug delivery, and chemical sensing. One of the longstanding chemical challenges in the engineering of nanomaterials is to control the placement of different chemistries in spatially distinct regions on a nanoscale object. This thesis focuses on discovering and understanding processes to prepare such spatially differentiated chemistries on porous silicon. For the porous silicon system...

  6. a Fractal Network Model for Fractured Porous Media

    Science.gov (United States)

    Xu, Peng; Li, Cuihong; Qiu, Shuxia; Sasmito, Agus Pulung

    2016-04-01

    The transport properties and mechanisms of fractured porous media are very important for oil and gas reservoir engineering, hydraulics, environmental science, chemical engineering, etc. In this paper, a fractal dual-porosity model is developed to estimate the equivalent hydraulic properties of fractured porous media, where a fractal tree-like network model is used to characterize the fracture system according to its fractal scaling laws and topological structures. The analytical expressions for the effective permeability of fracture system and fractured porous media, tortuosity, fracture density and fraction are derived. The proposed fractal model has been validated by comparisons with available experimental data and numerical simulation. It has been shown that fractal dimensions for fracture length and aperture have significant effect on the equivalent hydraulic properties of fractured porous media. The effective permeability of fracture system can be increased with the increase of fractal dimensions for fracture length and aperture, while it can be remarkably lowered by introducing tortuosity at large branching angle. Also, a scaling law between the fracture density and fractal dimension for fracture length has been found, where the scaling exponent depends on the fracture number. The present fractal dual-porosity model may shed light on the transport physics of fractured porous media and provide theoretical basis for oil and gas exploitation, underground water, nuclear waste disposal and geothermal energy extraction as well as chemical engineering, etc.

  7. Nanotube Arrays in Porous Anodic Alumina Membranes

    Institute of Scientific and Technical Information of China (English)

    Liang LI; Naoto KOSHIZAKI; Guanghai LI

    2008-01-01

    This review summarizes the various techniques developed for fabricating nanotube arrays in porous anodic alumina membranes (AAMs). After a brief introduction to the fabrication process of AAMs, taking carbons, metals, semiconductors, organics, biomoleculars, and heterojunctions as typical examples, attention will be focused on the recently established methods to fabricate nanotubes in AAM, including electrochemical deposition, surface sol-gel, modified chemical vapor deposition, atomic layer deposition, and layer-by-layer growth. Every method is demonstrated by one or two reported results. Finally, this review is concluded with some perspectives on the research directions and focuses on the AAM-based nanotubes fields.

  8. Teaching Heterogeneous Classes.

    Science.gov (United States)

    Millrood, Radislav

    2002-01-01

    Discusses an approach to teaching heterogeneous English-as-a-Second/Foreign-Language classes. Draws on classroom research data to describe the features of a success-building lesson context. (Author/VWL)

  9. Heterogeneous Calculation of ε

    International Nuclear Information System (INIS)

    A heterogeneous method of calculating the fast fission factor given by Naudet has been applied to the Carlvik - Pershagen definition of ε. An exact calculation of the collision probabilities is included in the programme developed for the Ferranti - Mercury computer

  10. Characterization of Porous Solids for Gas Transport Applications

    Czech Academy of Sciences Publication Activity Database

    Šolcová, Olga

    Bratislava: Slovak Society of Chemical Engineering, 2013 - (Markoš, J.), s. 4 ISBN 978-80-89475-09-4. [International Conference of Slovak Society of Chemical Engineering /40./. Tatranské Matliare (SK), 27.05.2013-31.05.2013] R&D Projects: GA ČR(CZ) GAP204/11/1206 Institutional support: RVO:67985858 Keywords : porous media * transport processes * material texture Subject RIV: CF - Physical ; Theoretical Chemistry

  11. Nanocarbon-Coated Porous Anodic Alumina for Bionic Devices

    OpenAIRE

    Morteza Aramesh; Wei Tong; Kate Fox; Ann Turnley; Dong Han Seo; Steven Prawer; Kostya (Ken) Ostrikov

    2015-01-01

    A highly-stable and biocompatible nanoporous electrode is demonstrated herein. The electrode is based on a porous anodic alumina which is conformally coated with an ultra-thin layer of diamond-like carbon. The nanocarbon coating plays an essential role for the chemical stability and biocompatibility of the electrodes; thus, the coated electrodes are ideally suited for biomedical applications. The corrosion resistance of the proposed electrodes was tested under extreme chemical conditions, su...

  12. Towards a rigorous mesoscale modeling of reactive flow and transport in an evolving porous medium and its applications to soil science

    Science.gov (United States)

    Ray, Nadja; Rupp, Andreas; Knabner, Peter

    2016-04-01

    Soil is arguably the most prominent example of a natural porous medium that is composed of a porous matrix and a pore space. Within this framework and in terms of soil's heterogeneity, we first consider transport and fluid flow at the pore scale. From there, we develop a mechanistic model and upscale it mathematically to transfer our model from the small scale to that of the mesoscale (laboratory scale). The mathematical framework of (periodic) homogenization (in principal) rigorously facilitates such processes by exactly computing the effective coefficients/parameters by means of the pore geometry and processes. In our model, various small-scale soil processes may be taken into account: molecular diffusion, convection, drift emerging from electric forces, and homogeneous reactions of chemical species in a solvent. Additionally, our model may consider heterogeneous reactions at the porous matrix, thus altering both the porosity and the matrix. Moreover, our model may additionally address biophysical processes, such as the growth of biofilms and how this affects the shape of the pore space. Both of the latter processes result in an intrinsically variable soil structure in space and time. Upscaling such models under the assumption of a locally periodic setting must be performed meticulously to preserve information regarding the complex coupling of processes in the evolving heterogeneous medium. Generally, a micro-macro model emerges that is then comprised of several levels of couplings: Macroscopic equations that describe the transport and fluid flow at the scale of the porous medium (mesoscale) include averaged time- and space-dependent coefficient functions. These functions may be explicitly computed by means of auxiliary cell problems (microscale). Finally, the pore space in which the cell problems are defined is time- and space dependent and its geometry inherits information from the transport equation's solutions. Numerical computations using mixed finite

  13. Colloid migration in porous media

    International Nuclear Information System (INIS)

    Retention of radionuclides for long periods near waste repositories depends upon multiple barriers, one of which is adsorption to immobile solid surfaces. Since small particles and colloidal matter have high adsorption capacities per unit mass and can be mobile in subsurface flows, colloidal transport of waste components requires analysis. Theories for predicting colloid migration through porous media have been developed in the filtration literature. The applicability of filtration theories for predicting particle and colloid transport. Emphasis is on suspended matter much smaller than pore sizes, where physical and chemical forces control migration rather than size dependent physical straining. In general, experimentally verifiable theories exist for particle filtration by clean media, and a sensitivity analysis is possible on particle and media properties and fluid flow rate. When particle aggregates accumulate within pores, media permeability decreases, resulting in flow field alteration and possible radionuclide isolation. An analysis of the limited experimental data available indicates that present theories cannot predict long-term colloid transport when permeability reduction occurs. The coupling of colloid attachment processes and the hydrologic flow processes requires more extensive laboratory field research than has currently been carried out. An emphasis on the fundamental mechanisms is necessary to enhance long-term predictability

  14. Predicting colloid transport through saturated porous media: A critical review

    Science.gov (United States)

    Molnar, Ian L.; Johnson, William P.; Gerhard, Jason I.; Willson, Clinton S.; O'Carroll, Denis M.

    2015-09-01

    Understanding and predicting colloid transport and retention in water-saturated porous media is important for the protection of human and ecological health. Early applications of colloid transport research before the 1990s included the removal of pathogens in granular drinking water filters. Since then, interest has expanded significantly to include such areas as source zone protection of drinking water systems and injection of nanometals for contaminated site remediation. This review summarizes predictive tools for colloid transport from the pore to field scales. First, we review experimental breakthrough and retention of colloids under favorable and unfavorable colloid/collector interactions (i.e., no significant and significant colloid-surface repulsion, respectively). Second, we review the continuum-scale modeling strategies used to describe observed transport behavior. Third, we review the following two components of colloid filtration theory: (i) mechanistic force/torque balance models of pore-scale colloid trajectories and (ii) approximating correlation equations used to predict colloid retention. The successes and limitations of these approaches for favorable conditions are summarized, as are recent developments to predict colloid retention under the unfavorable conditions particularly relevant to environmental applications. Fourth, we summarize the influences of physical and chemical heterogeneities on colloid transport and avenues for their prediction. Fifth, we review the upscaling of mechanistic model results to rate constants for use in continuum models of colloid behavior at the column and field scales. Overall, this paper clarifies the foundation for existing knowledge of colloid transport and retention, features recent advances in the field, critically assesses where existing approaches are successful and the limits of their application, and highlights outstanding challenges and future research opportunities. These challenges and opportunities

  15. Measurement of Fluid Flow in Pipe and Porous Media by High-Resolution Magnetic Resonance Imaging

    Institute of Scientific and Technical Information of China (English)

    JIANG Lan-lan; SONG Yong-chen; LIU Yu; DOU Bin-lin; ZHU Ning-jun; ZHAO Jia-fei; BULITI Abudula

    2012-01-01

    The objective of this study is to understand the process of fluid flow in pipe and porous media with different pore structures.High-resolution Magnetic Resonance Imaging (MRI) technique was used to visualize the pore structure and measure fluid flow.The porous media was formed by packed bed of glass beads.Flow measurement was carried out by a modified spin echo sequence.The results show that the velocity distribution in pipe is annular and the linear relation between MRI velocity and actual velocity is found in pipe flow measurement.The flow distribution in porous media is rather heterogeneous,and it is consistent with heterogeneous pore structure.The flow through pores with the high volume flow rate is determined largely by geometrical effects such as pore size and cross-sectional area.

  16. Atmospheric Pressure Microwave Assisted Heterogeneous Catalytic Reactions

    Directory of Open Access Journals (Sweden)

    Farid Chemat

    2007-07-01

    Full Text Available The purpose of the study was to investigate microwave selective heatingphenomena and their impact on heterogeneous chemical reactions. We also present a toolwhich will help microwave chemists to answer to such questions as “My reaction yields90% after 7 days at reflux; is it possible to obtain the same yield after a few minutes undermicrowaves?” and to have an approximation of their reactions when conducted undermicrowaves with different heterogeneous procedures. This model predicting reactionkinetics and yields under microwave heating is based on the Arrhenius equation, inagreement with experimental data and procedures.

  17. Mechanical transport and porous media equivalence in anisotropic fracture networks

    International Nuclear Information System (INIS)

    The objective of this work is to investigate the directional characteristics of hydraulic effective porosity in an effort to understand porous medium equivalence for continuous and discontinuous fracture systems. Continuous systems contain infinitely long fractures. Discontinuous systems consist of fractures with finite lengths. The distribution of apertures (heterogeneity) has a major influence on the degree of porous medium equivalence for distributed continuous and discontinuous systems. When the aperture distribution is narrow, the hydraulic effective porosity is slightly less than the total porosity for continuous systems, and greater than the rock effective porosity for discontinuous systems. However, when heterogeneity is significant, the hydraulic effective porosity is directionally dependent and greater than total porosity for both systems. Non-porous medium behavior ws found to differ for distributed continuous systems and for continuous systems with parallel sets. For the latter systems, hydraulic effective porosity abruptly decreases below total porosity in those particular directions where the hydraulic gradient and the orientation of a fracture set are orthogonal. The results for the continuous systems with parallel sets also demonstrate that a system that behaves like a continuum for fluid flux may not behave like a continuum for mechanical transport. 3 references, 13 figures

  18. Moisture Sorption in Porous Materials

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    2007-01-01

    Abstract: Information on pore geometry is very important in any study of the mechanical and physical behavior of porous materials. Unfortunately pores are not very accessible for direct measurements. Indirect methods have to be used which involve impregnation (sorption) experiments from which...... subject considered this software is available on request to the author. Keywords: Porous materials, moisture, adsorption, desorption, BET-parameters....

  19. Atomic Layer Epitaxial Growth of Gaas on Porous Silicon Substrate

    Directory of Open Access Journals (Sweden)

    Mohamed Lajnef

    2008-01-01

    Full Text Available GaAs thin film has been grown on porous silicon by metal organic chemical vapour deposition (MOCVD for different growth temperatures using atomic layer epitaxy (ALE technique. The morphology of GaAs layer was investigated by atomic force microscopy (AFM. The effect of growth temperature is studied using photoluminescence measurements (PL.The photoluminescence spectra revealed a dissymmetry form toward high energies attributed to strain effect resulting from the lattice mismatch between GaAs and porous Si substrate.

  20. Method for forming a chemical microreactor

    Science.gov (United States)

    Morse, Jeffrey D.; Jankowski, Alan

    2009-05-19

    Disclosed is a chemical microreactor that provides a means to generate hydrogen fuel from liquid sources such as ammonia, methanol, and butane through steam reforming processes when mixed with an appropriate amount of water. The microreactor contains capillary microchannels with integrated resistive heaters to facilitate the occurrence of catalytic steam reforming reactions. Two distinct embodiment styles are discussed. One embodiment style employs a packed catalyst capillary microchannel and at least one porous membrane. Another embodiment style employs a porous membrane with a large surface area or a porous membrane support structure containing a plurality of porous membranes having a large surface area in the aggregate, i.e., greater than about 1 m.sup.2/cm.sup.3. Various methods to form packed catalyst capillary microchannels, porous membranes and porous membrane support structures are also disclosed.