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| Titel |
Local rheology of foams in porous media: intermittency and bubble fragmentation |
| VerfasserIn |
Baudouin Géraud, Siân A. Jones, Benjamin Dollet, Isabelle Cantat, Yves Meheust |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250108069
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| Publikation (Nr.) |
 EGU/EGU2015-7800.pdf |
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| Zusammenfassung |
| Flowing foams are used in many engineering and technical applications. A well-known
application is oil recovery. Another one is the remediation of polluted soils: the foam is
injected into the ground in order to mobilize chemical species present in the medium. Apart
from potential interesting physico-chemical and biochemical properties, foams have peculiar
flow properties that applications might benefit of. In particular, viscous dissipation arises
mostly from the contact zones between the soap films and the walls, which results in
peculiar friction laws allowing the foam to invade narrow pores more efficiently than
Newtonian fluids would. In most experimental studies no local information of the foam
structure is possible, and only global quantities such as the effective viscosity can be
measured.
Using two-dimensional transparent flow cells, we have previously shown that foam
structural [1] and elastic [2] effects significantly impact the flow of foams in porous media.
We now present an investigation of foam flow through a two-dimensional (2D) porous
medium consisting of circular obstacles positioned randomly in a Hele-Shaw cell (see
figure). The foam structure is recorded in time by a video camera and subsequently
analyzed by image processing, which provides us with the velocity field and spatial
distribution of bubble sizes. The flow exhibits a rich phenomenology, including flow
irreversibility, preferential flow paths, local flow intermittency/non-stationarity (despite the
imposed permanent global flow rate). Moreover, the medium impacts the nature of
the flowing fluid by selecting the bubble size through bubble fragmentation. We
investigate how preferential flow paths and intermittency depend on the imposed
global flow rate and foam quality (the water content), and show that the spatial
distribution of bubble sizes is to some extent correlated with the velocity field.
We furthermore measure the evolution, along the flow direction, of the probability
density function for bubble sizes, and present a fragmentation model to explain that
evolution. It is controlled by two statistical distributions: that for the fragmentation
frequency of a bubble of given size a, f(a), and that for the size b of a bubble that
results from the fragmentation of a bubble of size a, g(a,b). Under simplifying
assumptions for the functions f(a) and g(a,b), an analytical resolution of the model’s
constitutive equation provides a behavior that is qualitatively similar to the experimental
observations. For more realistic assumptions, the solution can be obtained numerically.
We also attempted to infer the functions f(a) and g(a,b) from the experimental
data.
References:
[1] S. A. Jones, B. Dollet, Y. Méheust, S. J. Cox, I. Cantat, Phys. Fluids 25, 063101
(2013).
[2] B. Dollet, S. A. Jones, Y. Méheust, I. Cantat, Phys. Rev. E 90, 023006 (2014). |
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