The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Geoffrey R Tick - One of the best experts on this subject based on the ideXlab platform.
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peclet number as affected by Molecular Diffusion controls transient anomalous transport in alluvial aquifer aquitard complexes
Journal of Contaminant Hydrology, 2015Co-Authors: Yong Zhang, Christopher T. Green, Geoffrey R TickAbstract:Abstract This study evaluates the role of the Peclet number as affected by Molecular Diffusion in transient anomalous transport, which is one of the major knowledge gaps in anomalous transport, by combining Monte Carlo simulations and stochastic model analysis. Two alluvial settings containing either short- or long-connected hydrofacies are generated and used as media for flow and transport modeling. Numerical experiments show that 1) the Peclet number affects both the duration of the power-law segment of tracer breakthrough curves (BTCs) and the transition rate from anomalous to Fickian transport by determining the solute residence time for a given low-permeability layer, 2) mechanical dispersion has a limited contribution to the anomalous characteristics of late-time transport as compared to Molecular Diffusion due to an almost negligible velocity in floodplain deposits, and 3) the initial source dimensions only enhance the power-law tail of the BTCs at short travel distances. A tempered stable stochastic (TSS) model is then applied to analyze the modeled transport. Applications show that the time-nonlocal parameters in the TSS model relate to the Peclet number, Pe. In particular, the truncation parameter in the TSS model increases nonlinearly with a decrease in Pe due to the decrease of the mean residence time, and the capacity coefficient increases with an increase in Molecular Diffusion which is probably due to the increase in the number of immobile particles. The above numerical experiments and stochastic analysis therefore reveal that the Peclet number as affected by Molecular Diffusion controls transient anomalous transport in alluvial aquifer–aquitard complexes.
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Peclet number as affected by Molecular Diffusion controls transient anomalous transport in alluvial aquifer–aquitard complexes
Journal of Contaminant Hydrology, 2015Co-Authors: Yong Zhang, Christopher T. Green, Geoffrey R TickAbstract:Abstract This study evaluates the role of the Peclet number as affected by Molecular Diffusion in transient anomalous transport, which is one of the major knowledge gaps in anomalous transport, by combining Monte Carlo simulations and stochastic model analysis. Two alluvial settings containing either short- or long-connected hydrofacies are generated and used as media for flow and transport modeling. Numerical experiments show that 1) the Peclet number affects both the duration of the power-law segment of tracer breakthrough curves (BTCs) and the transition rate from anomalous to Fickian transport by determining the solute residence time for a given low-permeability layer, 2) mechanical dispersion has a limited contribution to the anomalous characteristics of late-time transport as compared to Molecular Diffusion due to an almost negligible velocity in floodplain deposits, and 3) the initial source dimensions only enhance the power-law tail of the BTCs at short travel distances. A tempered stable stochastic (TSS) model is then applied to analyze the modeled transport. Applications show that the time-nonlocal parameters in the TSS model relate to the Peclet number, Pe. In particular, the truncation parameter in the TSS model increases nonlinearly with a decrease in Pe due to the decrease of the mean residence time, and the capacity coefficient increases with an increase in Molecular Diffusion which is probably due to the increase in the number of immobile particles. The above numerical experiments and stochastic analysis therefore reveal that the Peclet number as affected by Molecular Diffusion controls transient anomalous transport in alluvial aquifer–aquitard complexes.
Yong Zhang - One of the best experts on this subject based on the ideXlab platform.
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peclet number as affected by Molecular Diffusion controls transient anomalous transport in alluvial aquifer aquitard complexes
Journal of Contaminant Hydrology, 2015Co-Authors: Yong Zhang, Christopher T. Green, Geoffrey R TickAbstract:Abstract This study evaluates the role of the Peclet number as affected by Molecular Diffusion in transient anomalous transport, which is one of the major knowledge gaps in anomalous transport, by combining Monte Carlo simulations and stochastic model analysis. Two alluvial settings containing either short- or long-connected hydrofacies are generated and used as media for flow and transport modeling. Numerical experiments show that 1) the Peclet number affects both the duration of the power-law segment of tracer breakthrough curves (BTCs) and the transition rate from anomalous to Fickian transport by determining the solute residence time for a given low-permeability layer, 2) mechanical dispersion has a limited contribution to the anomalous characteristics of late-time transport as compared to Molecular Diffusion due to an almost negligible velocity in floodplain deposits, and 3) the initial source dimensions only enhance the power-law tail of the BTCs at short travel distances. A tempered stable stochastic (TSS) model is then applied to analyze the modeled transport. Applications show that the time-nonlocal parameters in the TSS model relate to the Peclet number, Pe. In particular, the truncation parameter in the TSS model increases nonlinearly with a decrease in Pe due to the decrease of the mean residence time, and the capacity coefficient increases with an increase in Molecular Diffusion which is probably due to the increase in the number of immobile particles. The above numerical experiments and stochastic analysis therefore reveal that the Peclet number as affected by Molecular Diffusion controls transient anomalous transport in alluvial aquifer–aquitard complexes.
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Peclet number as affected by Molecular Diffusion controls transient anomalous transport in alluvial aquifer–aquitard complexes
Journal of Contaminant Hydrology, 2015Co-Authors: Yong Zhang, Christopher T. Green, Geoffrey R TickAbstract:Abstract This study evaluates the role of the Peclet number as affected by Molecular Diffusion in transient anomalous transport, which is one of the major knowledge gaps in anomalous transport, by combining Monte Carlo simulations and stochastic model analysis. Two alluvial settings containing either short- or long-connected hydrofacies are generated and used as media for flow and transport modeling. Numerical experiments show that 1) the Peclet number affects both the duration of the power-law segment of tracer breakthrough curves (BTCs) and the transition rate from anomalous to Fickian transport by determining the solute residence time for a given low-permeability layer, 2) mechanical dispersion has a limited contribution to the anomalous characteristics of late-time transport as compared to Molecular Diffusion due to an almost negligible velocity in floodplain deposits, and 3) the initial source dimensions only enhance the power-law tail of the BTCs at short travel distances. A tempered stable stochastic (TSS) model is then applied to analyze the modeled transport. Applications show that the time-nonlocal parameters in the TSS model relate to the Peclet number, Pe. In particular, the truncation parameter in the TSS model increases nonlinearly with a decrease in Pe due to the decrease of the mean residence time, and the capacity coefficient increases with an increase in Molecular Diffusion which is probably due to the increase in the number of immobile particles. The above numerical experiments and stochastic analysis therefore reveal that the Peclet number as affected by Molecular Diffusion controls transient anomalous transport in alluvial aquifer–aquitard complexes.
Jörg Kärger - One of the best experts on this subject based on the ideXlab platform.
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Structure-mobility relations of Molecular Diffusion in nanoporous materials.
Magnetic resonance imaging, 2003Co-Authors: Jörg Kärger, Frank Stallmach, Sergey VasenkovAbstract:Depending on the measuring conditions, pulsed field gradient (PFG) NMR measurements of Molecular Diffusion in beds of nanoporous particles may provide information about the propagation rate of guest molecules in both the intra- and interparticle spaces, as well as through the interface between them. Recent progress in both PFG NMR instrumentation and computational techniques have initiated studies of novel aspects in each of these areas, which are reviewed in this communication. They concern the possibility of multicomponent Diffusion measurements with ultra-high pulsed field gradients, the peculiarities of Molecular Diffusion in channel networks, the determination of the surface-to-volume ratio of nanoporous particles and the dependence of the tortuosity factor of long-range Diffusion on the Diffusion mode in the intercrystalline space.
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NMR evidence of anomalous Molecular Diffusion due to structural confinement
Europhysics Letters (EPL), 1996Co-Authors: M. Appel, Jörg Kärger, Gerald Fleischer, Franz Fujara, S. SiegelAbstract:Using the field gradient NMR technique, anomalous Molecular Diffusion in a porous host matrix of polypropylene could be followed over a substantial range of observation times. The experimentally determined time exponents of anomalous Diffusion are found to decrease with decreasing pore filling factors, indicating an enhancement of Molecular confinement. For sufficiently large observation times normal Diffusion is observed and the effect of confinement results in a mere reduction of the effective diffusivity, which is independent of the given Molecular species.
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Studies of Molecular Diffusion in porous crystals (zeolites)
Journal of Molecular Liquids, 1992Co-Authors: Harry Pfeifer, Jörg KärgerAbstract:Abstract The conventional way to study Molecular Diffusion in porous crystallites (zeolites) is to follow the rate of mass change of a sample after changing the pressure of the surrounding atmosphere, and it was one of the most important results of the application of NMR spectroscopy in interface science to show that intracrystalline Molecular Diffusion coefficients measured in this way were wrong up to five orders of magnitude. The NMR method applied in these measurements is the so-called pulsed field gradient (PFG NMR) technique. Its basic principles, the procedures of measurement and its limitations are discussed, and recent results are presented concerning the anisotropy of Molecular Diffusion in zeolites of non-cubic symmetry.
Hubert M. Pollock - One of the best experts on this subject based on the ideXlab platform.
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Surface Molecular Diffusion in latex films observed by atomic force microscopy
Polymer, 2001Co-Authors: Mo Song, Douglas J. Hourston, H.x. Zhang, Azzedine Hammiche, Hubert M. PollockAbstract:Abstract Surface Molecular Diffusion in a latex film has been investigated by atomic force microscopy. Deformation of the particles in the plane of the film of a real latex system did not change the centre-to-centre spacing, but the peak-to-valley distance y decreased upon annealing. The theoretical and also the experimental relationship between y and time t is given by the equation y(t)=y(0) exp (−t/τ) where τ is a constant, which is related to surface tension, particle size and the surface Molecular Diffusion coefficient. By measuring the change of y with time, the surface Molecular Diffusion coefficient may be obtained. The surface Molecular Diffusion coefficient for a poly(methyl methacrylate-co-butyl acrylate) (50:50) copolymer latex film at 65°C was found to be 0.9×10 −13 cm 2 / s . Surface Molecular Diffusion in the latex film is driven by the surface tension or surface free energy.
M. Mounir Bou-ali - One of the best experts on this subject based on the ideXlab platform.
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ThermoDiffusion, Molecular Diffusion and Soret coefficients of aromatic+n-alkane binary mixtures.
The Journal of chemical physics, 2016Co-Authors: Miren Larrañaga, M. Mounir Bou-ali, Estela Lapeira, Ion Lizarraga, Carlos SantamaríaAbstract:In the present work, we have measured the thermoDiffusion coefficient of 51 binary liquid mixtures at 25 oC. These mixtures correspond to the series of the aromatics toluene and 1-methylnaphthalene with n-alkanes nCi (i = 6, 8, 10, 12, and 14) at different mass fractions in the whole range. For that, we have used the thermogravitational technique. It is shown that the thermoDiffusion coefficient is a linear function of the mass fraction in all the mixtures. Extrapolating the lines, we obtain the thermoDiffusion coefficient in dilute solutions of n-alkanes for both toluene and 1-methylnaphthalene. These limiting values show a linear dependence with the inverse of the product of the Molecular weights. In addition, we have measured the Molecular Diffusion coefficient of all the mixtures at 0.5 of mass fraction and at 25 oC, by the sliding symmetric tubes technique. It is observed that the product of this coefficient with the viscosity at the same concentrations takes a constant value for each of the series considered. Finally, we have also determined the Soret coefficient of the equimass mixtures by the combination of the measurements of thermoDiffusion and Molecular Diffusion coefficients.
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ThermoDiffusion, Molecular Diffusion and Soret coefficient of binary and ternary mixtures of n-hexane, n-dodecane and toluene.
The European physical journal. E Soft matter, 2014Co-Authors: David Alonso De Mezquia, Estela Lapeira, Zilin Wang, Michael Klein, Simone Wiegand, M. Mounir Bou-aliAbstract:In this study, the thermoDiffusion, Molecular Diffusion, and Soret coefficients of 12 binary mixtures composed of toluene, n-hexane and n-dodecane in the whole range of concentrations at atmospheric pressure and temperatures of 298.15 K and 308.15 K have been determined. The experimental measurements have been carried out using the Thermogravitational Column, the Sliding Symmetric Tubes and the Thermal Diffusion Forced Rayleigh Scattering techniques. The results obtained using the different techniques show a maximum deviation of 9% for the thermoDiffusion coefficient, 8% for the Molecular Diffusion coefficient and 2% for the Soret coefficient. For the first time we report a decrease of the thermoDiffusion coefficient with increasing ratio of the thermal expansion coefficient and viscosity for a binary mixture of an organic ring compound with a short n-alkane. This observation is discussed in terms of interactions between the different components. Additionally, the thermogravitational technique has been used to measure the thermoDiffusion coefficients of four ternary mixtures consisting of toluene, n-hexane and n-dodecane at 298.15 K. In order to complete the study, the values obtained for the Molecular Diffusion coefficient in binary mixtures, and the thermoDiffusion coefficient of binary and ternary mixtures have been compared with recently derived correlations.
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Determination of the Molecular Diffusion coefficients in ternary mixtures by the sliding symmetric tubes technique
The Journal of chemical physics, 2014Co-Authors: Miren Larrañaga, D. Andrew S. Rees, M. Mounir Bou-aliAbstract:A new analytical methodology has been developed to determine the diagonal and cross-diagonal Molecular Diffusion coefficients in ternary mixtures by the Sliding Symmetric Tubes technique. The analytical solution is tested in binary mixtures obtaining good agreement with the results of the literature. Results are presented for the ternary mixture formed by tetralin, isobutylbenzene, and dodecane with an equal mass fraction for all the components (1–1–1) which is held at 25 °C. Diagonal and cross-diagonal coefficients are determined for the three possible orders of components, in order to compare the results with those available in the literature. A comparison with published results shows a good agreement for the eigenvalues of the Diffusion matrix, and a reasonable agreement for the diagonal Molecular Diffusion coefficients.
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ThermoDiffusion and Molecular Diffusion in binaryn-alkane mixtures: experiments and numerical analysis
Philosophical Magazine, 2011Co-Authors: Seshasai Srinivasan, D. Alonso De Mezquia, M. Mounir Bou-ali, M. Z. SaghirAbstract:New experimental data on the thermoDiffusion and Molecular Diffusion coefficients of nine non-equimolar binary mixtures of ( ) at 298 K and 1 atm have been reported. The data have been obtained using a combination of the thermogravitational column and the sliding symmetric tubes technique, respectively. It was found that with an increase in the disparity between the two components, the Soret effect becomes more dominant. Further, the stronger Soret effect weakens the Molecular Diffusion process. These trends are observed in the form of an increase in magnitude of the thermoDiffusion coefficient and a decrease in the magnitude of the Molecular Diffusion coefficient. Numerical analysis was also performed using the principles of non-equilibrium thermodynamics. The model was able to predict the experimental data as well as the trends fairly accurately.