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| Titel |
Anomalous kinetics of reactive front in Porous Media |
| VerfasserIn |
P. de Anna, A. M. Tartakovsky, T. Le Borgne, M. Dentz |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060863
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| Zusammenfassung |
| Natural flow fields in porous media display a complex spatio-temporal organization due to
heterogeneous geological structures at different scales. This multiscale disorder implies
anomalous transport properties (e.g. Berkowitz et al. RG 2006). Here, we show that it also
implies anomalous mixing and reaction kinetics. This effect arises from pore scale, non
Gaussian and correlated, velocity distributions.
We consider a reactive front, where a component A displaces a component B that
saturates initially the porous domain. The reactive component C is produced at the front
located at interface between the A and B domains. We investigate the effective kinetics for the
mixing limited bimolecular reaction A + B - C in a 2D porous medium. The system is
studied numerically via the SPH method.
While Fickian diffusion predicts a scaling of the cumulative mass of C as t0.5 (e.g.
Gramling et al. 2002), we observe that the temporal evolution of the cumulative mass of
reaction product does not follow this classical law. Two temporal regimes are identified. At
early times the invading solute is organized in fingers of high velocity. Reactions are fast and
the mass product grows as t2. At late times reactions slow down but still grow faster than
Fickian case. We discuss the different scaling regimes arising depending on the dominant
process that governs mixing.
In order to upscale these processes, we analyze the Lagrangian velocity properties, which
are characterized by the non Gaussian distributions and long range temporal correlation. The
main origin of these properties is the existence of very low velocity regions where solute
particles can remain trapped for a long time and the channeling of flow in localized high
velocity regions, which created finger-like structures in the concentration field. |
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