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  • 1
    Electronic Resource
    Electronic Resource
    Improved atomistic simulation of diffusion and sorption in metal oxides (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 545-552 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Gas diffusion and sorption on the surface of metal oxides are investigated using atomistic simulations, that make use of two different force fields for the description of the intramolecular and intermolecular interactions. MD and MC computations are presented and estimates of the mean residence time, Henry's constant, and the heat of adsorption are provided for various common gases (CO, CO2, O2, CH4, Xe), and semiconducting substrates that hold promise for gas sensor applications (SnO2, BaTiO3). Comparison is made between the performance of a simple, first generation force field (Universal) and a more detailed, second generation field (COMPASS) under the same conditions and the same assumptions regarding the generation of the working configurations. It is found that the two force fields yield qualitatively similar results in all cases examined here. However, direct comparison with experimental data reveals that the accuracy of the COMPASS-based computations is not only higher than that of the first generation force field but exceeds even that of published specialized methods, based on ab initio computations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1330727
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamics of Oil Ganglia During Immiscible Displacement in Water-Wet Porous Media (1982)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 14 (1982), S. 365-393 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fl.14.010182.002053
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  • 3
    Electronic Resource
    Electronic Resource
    Simulation of gas diffusion and sorption in nanoceramic semiconductors (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 9244-9253 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Gas diffusion and sorption in nanoceramic semiconductors are studied using atomistic simulation techniques and numerical results are presented for a variety of sorbate–sorbent systems. SnO2, BaTiO3, CuO, and MgO substrates are built on the computer using lattice constants and atomic parameters that have been either measured or computed by ab initio methods. The Universal force field is employed here for the description of both intramolecular and nonbonded interactions for various gas sorbates, including CH4, CO, CO2, and O2, pure and in binary mixtures. Mean residence times are determined by molecular dynamics computations, whereas the Henry constant and the isosteric heat of adsorption are estimated by a Monte Carlo technique. The effects of surface hydroxylation on the diffusion and sorption characteristics are quantified and discussed in view of their significance in practical gas sensing applications. The importance of fast diffusion on the response time of the sensitive layer and of the sorption efficiency on the overall sensitivity as well as the potential synergy of the two phenomena are discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478848
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanistic Model of Steady-State Two-Phase Flow in Porous Media Based on Ganglion Dynamics (1998)
    Springer
    Transport in porous media 30 (1998), S. 267-299 
    Details
    ISSN: 1573-1634
    Keywords: two-phase flow ; ganglion dynamics ; relative permeability ; population balance equations ; oil recovery ; soil remediation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Recent experimental work has shown that the pore-scale flow mechanism during steady-state two-phase flow in porous media is ganglion dynamics (GD) over a broad and practically significant range of the system parameters. This observation suggests that our conception and theoretical treatment of fractional flow in porous media need careful reconsideration. Here is proposed a mechanistic model of steady-state two-phase flow in those cases where the dominant flow regime is ganglion dynamics. The approach is based on the ganglion population balance equations in combination with a microflow network simulator. The fundamental information on the cooperative flow behavior of the two fluids at the scale of a few hundred pores is expressed through the system factors, which are functions of the system parameters and are calculated using the simulator. These system factors are utilized by the population balance equations to predict the macroscopic behavior of the process. The dependence of the conventional relative permeability coefficients not only on the wetting fluid saturation Swbut also on the capillary number, Ca, the viscosity ratio κ the wettability (θ0 a, θ0 r), the coalescence factor, Co, as well as the porous medium geometry and topology is explained and predicted on a mechanistic basis. Sample calculations have been performed for steady-state fully developed (SSFD) and steady-state nonfully developed (SSnonFD) flow conditions. The number distributions of the moving and the stranded ganglia, the mean ganglion size, the fraction of the nonwetting fluid in the form of mobile ganglia, the ratio of the conventional relative permeability coefficients and the fractional flows are studied as functions of the system parameters and are correlated with the flow phenomena at pore level and the system factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006558121674
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  • 5
    Electronic Resource
    Electronic Resource
    Steady-state two-phase flow through planar and nonplanar model porous media (1994)
    Springer
    Transport in porous media 16 (1994), S. 75-101 
    Details
    ISSN: 1573-1634
    Keywords: two-phase flow ; ganglion dynamics ; immiscible displacement ; relative permeability ; enhanced oil recovery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A comparative experimental study of ‘steady-state’ two-phase flow in two types of model porous media is made to determine the effects of nonplanarity on the flow mechanisms and the mesoscopic flow behavior. The two model porous media have virtually the same pore geometry, but one has a planar network skeleton, whereas the other has a nonplanar (two-layer) skeleton. The latter is a new type of model porous medium that permits detailed visual observation and quantitative measurements without sacrificing the 3D character of the pore network topology. The capillary number and the flowrate ratio are changed systematically, whereas the viscosity ratio and the wettability (contact angle) are kept constant. Conventional relative permeabilities are determined and correlated with the porescale flow phenomena. In the range of parameter values investigated, the flow mechanism observed was ganglion dynamics (intrinsically unsteady, but giving a time-averaged steady-state). The nonplanarity is shown to have small qualitative but significant quantitative effects. In the nonplanar porous medium, the ganglion size distribution is wider, the mean ganglion size larger, and the stranded ganglia are fewer than those in the planar one, under the same flow conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01059777
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  • 6
    Electronic Resource
    Electronic Resource
    Generalized relative permeability coefficients during steady-state two-phase flow in porous media, and correlation with the flow mechanisms (1995)
    Springer
    Transport in porous media 20 (1995), S. 135-168 
    Details
    ISSN: 1573-1634
    Keywords: two-phase flow ; relative permeabilities ; ganglion dynamics ; viscous coupling ; coupling indices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A parametric experimental investigation of the coupling effects during steady-state two-phase flow in porous media was carried out using a large model pore network of the chamber-and-throat type, etched in glass. The wetting phase saturation,S 1, the capillary number,Ca, and the viscosity ratio,k, were changed systematically, whereas the wettability (contact angleθ e ), the coalescence factorCo, and the geometrical and topological parameters were kept constant. The fluid flow rate and the pressure drop were measured independently for each fluid. During each experiment, the pore-scale flow mechanisms were observed and videorecorded, and the mean water saturation was determined with image analysis. Conventional relative permeability, as well as generalized relative permeability coefficients (with the viscous coupling terms taken explicitly into account) were determined with a new method that is based on a B-spline functional representation combined with standard constrained optimization techniques. A simple relationship between the conventional relative permeabilities and the generalized relative permeability coefficients is established based on several experimental sets. The viscous coupling (off-diagonal) coefficients are found to be comparable in magnitude to the direct (diagonal) coefficients over board ranges of the flow parameter values. The off-diagonal coefficients (k rij /Μ j ) are found to be unequal, and this is explained by the fact that, in the class of flows under consideration, microscopic reversibility does not hold and thus the Onsager-Casimir reciprocal relation does not apply. Thecoupling indices are introduced here; they are defined so that the magnitude of each coupling index is the measure of the contribution of the coupling effects to the flow rate of the corresponding fluid. A correlation of the coupling indices with the underlying flow mechanisms and the pertinent flow parameters is established.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00616928
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  • 7
    Electronic Resource
    Electronic Resource
    Further work on the flow through periodically constricted tubes - a reply (1973)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 19 (1973), S. 1036-1039 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690190523
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  • 8
    Electronic Resource
    Electronic Resource
    Dendritic deposition of aerosols by convective Brownian diffusion for small, intermediate and high particle Knudsen numbers (1980)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 26 (1980), S. 443-454 
    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: When an aerocolloidal suspension flows through a fibrous filter, particles deposit on the fibers and form dendrites. Similar phenomena are observed with collectors other than fibers, provided that the characteristic dimension of the collector does not exceed that of the particles by more than one to two orders of magnitude. This deposition pattern leads to marked increases in capture efficiency and pressure drop, as particles accumulate within the filter. In previous publications, theoretical models of this process were developed for the cases of deposition by interception alone and of deposition by combined inertial impaction and interception. Consequently, those works apply to aerosol particles with diameters of 1 μm or larger. Here we extend the model to the case of submicron particles, where the main transport mechanism is Brownian diffusion. To keep things specific, we consider fine fibers as collectors, but the model can be easily converted to other geometries. We present solutions for the cases of nonslip flow around the fiber and nonslip, slip and free molecular flow around particles. Unlike deposition by inertial impaction and/or interception, convective Brownian diffusion forms dendrites over the entire fiber surface.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690260316
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  • 9
    Electronic Resource
    Electronic Resource
    Oil ganglion dynamics during immiscible displacement: Model formulation (1980)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 26 (1980), S. 430-443 
    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: A model is formulated in order to study the transient behavior of oil ganglion populations during immiscible displacement in oil recovery processes. The model is composed of three components: a suitable model for granular porous media; a stochastic simulation method capable of predicting the expected fate (mobilization, breakup, stranding) of solitary oil ganglia moving through granular porous media; and two coupled ganglion population balance equations, one applying to moving ganglia and the other to stranded ones. The porous medium model consists of a regular network of randomly sized unit cells of the constricted tube type. Based on this model and a mobilization-breakup criterion, computer aided simulations provide probabilistic information concerning the fate of solitary oil ganglia. Such information is required in the ganglion population balance equations, the solution of which delineates the conditions under which oil bank formation suceeds or fails. Successful oil bank formation depends on the outcome of the competition between the process of oil ganglion deterioration through breakup and stranding on one hand and the process of oil ganglion collision and coalescence on the other. The parameters entering the system of population balances are initial ganglion number concentration, average ganglion velocity, ganglion dispersion coefficients, ganglion stranding coefficient, ganglion breakup coefficient and probability of coalescence given a collision. These parameters are, in turn, functions of the porous medium geometry, capillary number, ganglion size distribution, flood velocity, oil saturation and flood composition.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690260315
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  • 10
    Electronic Resource
    Electronic Resource
    Collocation solution of creeping newtonian flow through sinusoidal tubes: A correctionA. C. Payatakes is also at the Department of Chemical Engineering, Polytechnic School, University of Patras, Patras, Greece. (1984)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 30 (1984), S. 1016-1021 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690300628
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