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  • Artikel  (9)
  • Electronic structure and strongly correlated systems
  • Humans
  • biocompatibility
  • dispersion
  • 1990-1994  (9)
  • Technik allgemein  (9)
  • 1
    Digitale Medien
    Digitale Medien
    A computerized technique for measuringin-situ concentrations during miscible displacements in porous media (1992)
    Springer
    Transport in porous media 7 (1992), S. 127-145 
    Details
    ISSN: 1573-1634
    Schlagwort(e): Miscible displacement ; dispersion ; in-situ concentration measurement ; computerized data acquisition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract A technique for measurement of thein-situ concentration in an unconsolidated porous medium has been developed. The method involves measurement of electrical conductivityin-situ, under dynamic conditions, for flow involving brine of differing concentrations, at selected locations along the porous medium and relating it to the brine strength. Data acquisition and analysis is carried out using a Hewlett — Packard micro-computer and its interface. A user-friendly software was designed and developed for the system. The measurement technique was evaluated by studying the effect of brine concentration, brine flow rate, and by conducting miscible displacements experiment. The experimentally measured dispersion coefficients for the porous medium agreed closely with the value predicted by the correlation available in the literature.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00647393
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  • 2
    Digitale Medien
    Digitale Medien
    Waves in partially saturated porous media (1992)
    Springer
    Transport in porous media 9 (1992), S. 25-37 
    Details
    ISSN: 1573-1634
    Schlagwort(e): Waves ; dispersion ; shock tube ; gas bubbles
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract The propagation of compressional waves in a porous medium is investigated in case the pore liquid contains a small volume fraction of gas. The effect of oscillating gas bubbles is taken into account by introducing a frequency-dependent fluid bulk modulus, which is incorporated in the Biot theory. Using a shock tube technique, new experimental data are obtained for a porous column subjected to a pressure step wave. An oscillatory behaviour is observed, consisting of two distinct frequency bands, which is predicted by the theoretical analysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01039623
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  • 3
    Digitale Medien
    Digitale Medien
    Scaling mixing during miscible displacement in heterogeneous porous media (1991)
    Springer
    Transport in porous media 6 (1991), S. 607-626 
    Details
    ISSN: 1573-1634
    Schlagwort(e): dispersion ; dispersivity ; heterogenity ; miscible ; porous media ; scaling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract This paper discusses scaling of mixing during miscible flow in heterogeneous porous media. In large field systems dispersivity appears to depend on system length due to heterogeneities. Three types of scaling are discussed to investigate the heterogeneous effects. Dimensional analysis of mixing during flow through geometerically scaled heterogeneous models is illustrated using measured dispersion. Fractal analysis of mixing in statistically scaled heterogeneous porous media is discussed. Analog scaling of pressure transients in heterogeneous porous media is suggested as an in-situ method of estimating dispersion.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00137852
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  • 4
    Digitale Medien
    Digitale Medien
    Modelling fluid flow in cross-bedded sections (1993)
    Springer
    Transport in porous media 12 (1993), S. 143-159 
    Details
    ISSN: 1573-1634
    Schlagwort(e): Heterogeneity ; layers ; displacement ; numerical simulation ; flow in porous media ; dispersion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract Beadpack experiments and numerical simulations have been carried out to study flow displacements, effluent profiles and streamline patterns for layered systems with flow not parallel to the layers. The effects of layer thickness, permeability contrast, angle of layer to flow direction, mobility ratio and flood rate have been examined. Each of these parameters influence the displacement profiles, and disperse the flood front. Such real effects must be considered when subsuming reservoir heterogeneities in average reservoir parameters in simulation studies, or interpreting core tests.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00616977
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  • 5
    Digitale Medien
    Digitale Medien
    Fractal and superdiffusive transport and hydrodynamic dispersion in heterogeneous porous media (1993)
    Springer
    Transport in porous media 13 (1993), S. 3-40 
    Details
    ISSN: 1573-1634
    Schlagwort(e): Diffusion ; dispersion ; percolation ; fractals ; scaling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract We review and discuss diffusion and hydrodynamic dispersion in a heterogeneous porous medium. Two types of heterogeneities are considered. One is percolation disorder in which a fraction of the pores do not allow transport to take place at all. In the other type, the permeabilities of various regions of the pore space are fractally distributed with long-range correlations. Both systems give rise to unusual transport in which the mean square displacement 〈r 2(t)〉 of a particle grows nonlinearly with time. Depending on the heterogeneities and the mechanism of diffusion and disperison, we may havefractal transport in which 〈r 2〉 growsslower than linearly with time, orsuperdiffusive transport in which 〈r 2〉 growsfaster than linearly with time. We show that percolation models can give rise to both types of transport with scale-dependent transport coefficients such as diffusivity and dispersion coefficients, which are consistent with many experimental observations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00613269
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  • 6
    Digitale Medien
    Digitale Medien
    A theory of macrodispersion for the scale-up problem (1993)
    Springer
    Transport in porous media 13 (1993), S. 97-122 
    Details
    ISSN: 1573-1634
    Schlagwort(e): Scale up ; dispersion ; porous media ; random field
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract Dispersion is the result, observable on large length scales, of events which are random on small length scales. When the length scale on which the randomness operates is not small, relative to the observations, then classical dispersion theory fails. The scale up problem refers to situations in which randomness occurs on all length scales, and for which classical dispersion theory necessarily fails. The purpose of this article is to present non-Fickian, theories of dispersion, which do not assume a scale separation between the randomness and the observed consequences, and which do not assume a single length scale. Porous media flow properties are heterogeneous on all length scales. The geological variation on length scales below the observational length scale can be regarded as unknown and unknowable, and thus as a random variable. We develop a systematic theory relating scaling behavior of the geological heterogeneity to the scaling behavior of the fluid dispersivity. Three qualitatively distinct regimes (Fickian, non-Fickian and nonrenormalizable) are found. The theory gives consistent answers within several distinct analytic approximations, and with numerical simulation of the equations of porous media flow. Comparison to field data is made. The use of Kriging to generate constrained ensembles for conditional simulation is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00613272
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  • 7
    Digitale Medien
    Digitale Medien
    An experimental investigation of dispersion in layered porous media (1994)
    Springer
    Transport in porous media 15 (1994), S. 15-30 
    Details
    ISSN: 1573-1634
    Schlagwort(e): Experiment ; dispersion ; layered heterogeneity ; permeability ; averaging ; permutation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract Experiments were run in three linear, homogeneous, nonuniform porous media constructed in lucite columns using spherical glass beads. The columns were also joined end to end to create an in series layered heterogeneous porous media. Each column, all combinations of columns and several permutations were studied with a factorial experimental design to determine the effects of porosity, permeability, velocity, length, and column order upon dispersion. Attempts to predict the heterogeneous results from the homogeneous results were made, and a statistical regression based on the factorial design was calculated. Results showed that no simple averaging procedure accurately predicted the heterogeneous results. The statistical regression showed permeability, velocity, viscosity, length and column order to be significant.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01046156
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  • 8
    Digitale Medien
    Digitale Medien
    A LGA model for dispersion in heterogeneous porous media (1994)
    Springer
    Transport in porous media 17 (1994), S. 19-32 
    Details
    ISSN: 1573-1634
    Schlagwort(e): LGA model ; heterogeneous porous media ; miscible displacement ; dispersion ; tracer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Technik allgemein
    Notizen: Abstract The lattice gas automaton (LGA) model proposed in the previous paper is applied to the problem of simulating dispersion and mixing in heterogeneous porous media. We demonstrate here that tracer breakthrough profiles and longitudinal dispersion coefficients can be computed for heterogeneous porous media.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00624048
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  • 9
    Digitale Medien
    Digitale Medien
    Influence of the viscoelastic properties of the respiratory system on the energetically optimum breathing frequency (1993)
    Springer
    Annals of biomedical engineering 21 (1993), S. 489-499 
    Details
    ISSN: 1573-9686
    Schlagwort(e): Work of breathing ; Inspiratory pressure-time integral ; Respiratory modeling ; Dogs ; Humans
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Technik allgemein
    Notizen: Abstract We hypothesized that the viscoelastic properties of the respiratory system should have significant implications for the energetically optimal frequency of breathing, in view of the fact that these properties cause marked dependencies of overall system resistance and elastance on frequency. To test our hypothesis we simulated two models of canine and human respiratory system mechanics during sinusoidal breathing and calculated the inspiratory work ( $$\dot W$$ ) and pressure-time integral (PTI) per minute under both resting and exercise conditions. The two models were a two-compartment viscoelastic model and a single-compartment model. Requiring minute alveolar ventilation to be fixed, we found that both models predicted almost identical optimum breathing frequencies. The calculated PTI was very insensitive to increases in breathing frequency above the optimal frequencies, while $$\dot W$$ was found to increase slowly with frequency above its optimum. In contrast, both $$\dot W$$ and PTI increased sharply as frequency decreased below their respective optima. A sensitivity analysis showed that the model predictions were very insensitive to the elastance and resistance values chosen to characterize tissue viscoelasticity. We conclude that the $$\dot W$$ criterion for choosing the frequency of breathing is compatible with observations in nature, whereas the optimal frequency predictions of the PTI are rather too high. Both criteria allow for a fairly wide margin of choice in frequency above the optimum values without incurring excessive additional energy expenditure. Furthermore, contrary to our expectations, the viscoelastic properties of the respiratory system tissues do not pose a noticeable problem to the respiratory controller in terms of energy expenditure.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00000004
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