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  • 1995-1999  (8)
  • 1
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of gas mixtures in porous media. I. Adsorption (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 2178-2188 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper and its sequel we report the results of Molecular Dynamics simulation of single component and binary gas mixtures in a porous medium with interconnected pores. The porous medium used in the study is a model pillared clay. In the present paper we study adsorption of binary gas mixtures, and investigate in detail the effect of various factors, such as the morphology of the pore space and the adsorbent-adsorbate interactions. A new mean-field statistical mechanical theory of adsorption is developed, and shown to provide very accurate predictions for the simulation results over wide ranges of the pressure, temperature and porosity of the system. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475598
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Nonequilibrium molecular dynamics simulation of transport and separation of gases in carbon nanopores. I. Basic results (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3252-3264 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the results of extensive nonequilibrium Molecular Dynamics simulations of transport of a binary gas mixture of CO2 and CH4 through a carbon nanopore, in the presence of an external chemical potential or concentration gradient. The CH4 molecules are represented as Lennard-Jones (LJ) hard spheres, while the CO2 molecules are modeled both as LJ hard spheres, as well as three-site linear structures to account for their quadrupole moments. The effect of the various factors, including the structure of the pore walls, temperature, feed composition, and the molecular models and their parameters, on the transport, adsorption, and separation of the gases is investigated in detail. While the structure of the pore walls has virtually no effect on the separation factor, the temperature of the system, the pore size, and the molecular models and their parameters strongly influence it. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479663
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  • 3
    Electronic Resource
    Electronic Resource
    On position-space renormalization group approach to percolation (1995)
    Springer
    Journal of statistical physics 78 (1995), S. 1157-1164 
    Details
    ISSN: 1572-9613
    Keywords: Percolation ; renormalization ; universality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In a position-space renormalization group (PSRG) approach to percolation one calculates the probabilityR(p,b) that a finite lattice of linear sizeb percolates, wherep is the occupation probability of a site or bond. A sequence of percolation thresholdsp c (b) is then estimated fromR(p c ,b)=p c (b) and extrapolated to the limitb→∞ to obtainp c =p c (∞). Recently, it was shown that for a certain spanning rule and boundary condition,R(p c ,∞)=R c is universal, and sincep c is not universal, the validity of PSRG approaches was questioned. We suggest that the equationR(p c ,b)=α, where α isany number in (0,1), provides a sequence ofp c (b)'s thatalways converges top c asb→∞. Thus, there is anenvelope from any point inside of which one can converge top c . However, the convergence is optimal if α=R c . By calculating the fractal dimension of the sample-spanning cluster atp c , we show that the same is true aboutany critical exponent of percolation that is calculated by a PSRG method. Thus PSRG methods are still a useful tool for investigating percolation properties of disordered systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02183708
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  • 4
    Electronic Resource
    Electronic Resource
    Reply to ‘comment on fractal and superdiffusive transport and hydrodynamic dispersion in heterogeneous porous media’ (1995)
    Springer
    Transport in porous media 21 (1995), S. 189-194 
    Details
    ISSN: 1573-1634
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00613756
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of long-range correlations on transport phenomena in disordered media (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 229-240 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Three different flow and transport phenomena considered here are hydrodynamic dispersion in heterogeneous porous media and aquifers, transport of passive particles in an oscillating flow field, and miscible displacement processes in heterogeneous reservoirs. At microscales all three phenomena are described by the classical convective-diffusion equation (CDE). The presence of long-range correlations at macroscales gives rise to a rich variety of phenomena that cannot be predicted by analyzing the CDE by classical methods. In particular, a new percolation model with long-range correlations provides a rational explanation for the hitherto unexplained field-scale experimental data for hydrodynamic dispersion in porous media and aquifers. Moreover, for transport in oscillating flow in convection cells percolation provides a novel relation between the dispersion coefficient and the Péclet number that cannot be predicted by other methods.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690410205
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  • 6
    Electronic Resource
    Electronic Resource
    Asphalt flocculation and deposition: II. Formation and growth of fractal aggregates (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 3318-3332 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Extensive small-angle X-ray and neutron-scattering data, as well as results of precipitation measurements, are analyzed to delineate the structure of the asphalt and asphaltene aggregates that are formed when a solvent is injected into a system containing crude oil. The two types of data strongly suggest that both small and large aggregates have a fractal structure, with well-defined fractal dimensions. If the system is aged long enough at low enough temperature, large asphalt particles will have the structure of diffusion-limited cluster-cluster aggregates with a fractal dimension Df ≃ 1.8, while the small ones are similar to diffusion-limited particle aggregates with a fractal dimension df ≃ 2.5. High temperatures increase the rotational motion of the particles, disturb the structure and mechanical stability of the aggregates, and decrease their fractal dimension. Aging and concentration effects of the asphalts in the solution, and the type of the solvent on the structure of the aggregates are also investigated. Implications of these results for the structure, mechanical stability, and molecular-weight distribution of asphalts and asphaltenes are detailed. A new molecular-weight distribution for asphalt aggregates predicts the experimental data excellently.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690421204
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  • 7
    Electronic Resource
    Electronic Resource
    Asphalt flocculation and deposition: I. The onset of precipitation (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 10-22 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Formation of asphalt aggregates and their deposition on the pore surfaces of a porous medium, which alter the structure of the medium and its effective properties, is a critical problem to catalytic and oil recovery and refinery processes. Extensive new experimental data for the amount of precipitated asphalt formed with crude oil and various solvents are presented. Results indicate that, contrary to the previous assumptions, asphalt formation is at best partially reversible. A thermodynamic model based on the Flory-Huggins theory of polymer solutions is used, together with the Soave equation of state, to predict the data. Critical evaluation of the model shows that its predictions do not agree well with our data. As an alternative, we propose a new model that employs a scaling equation, somewhat similar to those encountered in aggregation and gelation phenomena. The scaling function takes on a very simple form, and its predictions are in very good agreement with the data. It also predicts that the onset of precipitation may obey a simple universal equation.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690420104
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  • 8
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulation of diffusion in pillared clays (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 456-468 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The thermodynamics and transport properties of Lennard-Jones particles in pillared catalytic clays are studied by molecular dynamics simulation. The clays are represented by parallel sheets separated by a given distance and connected by pillars of a given size. Two different spatial distributions of the pillars are studied to determine their effect on the properties of the system. Calculations did not indicate a strong dependence of the diffusivity on the spatial distribution of the pillars, except at low porosities. The solvation force increases monotonically with decreasing porosity of the clays and increasing density of the molecules. The percolation threshold ϕc of the system is estimated from the diffusivity measurements in the limit of infinitely low sorbate densities. Near ϕc the diffusivity D vanishes according to the power law, D ˜ (ϕ - ϕc)n, where ϕ is the porosity of the system, and n is a universal constant. The simulations yield n ⋍ 1.7. Since 2- percolation systems require n ⋍ 1.3 and 3-D systems n ⋍ 2.0, pillared clays behave as a system with an effective dimensionality between 2 and 3.
    Additional Material: 24 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690410304
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