Electronic Resource
New York, NY
:
American Institute of Physics (AIP)
Physics of Fluids
5 (1993), S. 1952-1962
ISSN:
1089-7666
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Tracer dispersion is studied in a plane fracture geometry with a radial flow between closely spaced parallel walls with either two smooth surfaces or one smooth and one rough surface. An echo dispersion technique in which the fluid is first injected into the fracture during a time Tinv and then pumped back through a detector is used in the experiments and is complemented by Monte-Carlo-type numerical simulations. For the smooth wall case, the Taylor dispersion mechanism is dominant when longitudinal molecular diffusion is negligible: it is verified numerically and experimentally that its transition to irreversibility only depends on the ratio of Tinv to the transverse diffusion time τm across the fracture thickness. In addition, the variation of Δ¯T¯2/(4Tinvτm) with respect to Tinv/τm is the same as for a flow of parallel geometry (Δ¯T¯2 being the mean square deviation of the transit time). Longitudinal molecular diffusion increases the global dispersion like Tinv/(PeQτm) at low Péclet numbers PeQ and long times due to the longitudinal velocity gradient. When one of the walls is rough, one expects to have a geometrical dispersion locally proportional to the velocity. A corresponding linear variation of Δ¯T¯2/(4Tinvτm) with respect to (square root of)Tinv/PeQ is observed experimentally.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.858822
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