40 research outputs found
Influence of the disorder on tracer dispersion in a flow channel
Tracer dispersion is studied experimentally in periodic or disordered arrays
of beads in a capillary tube. Dispersion is measured from light absorption
variations near the outlet following a steplike injection of dye at the inlet.
Visualizations using dye and pure glycerol are also performed in similar
geometries. Taylor dispersion is dominant both in an empty tube and for a
periodic array of beads: the dispersivity increases with the P\'eclet
number respectively as and and is larger by a factor of 8
in the second case. In a disordered packing of smaller beads (1/3 of the tube
diameter) geometrical dispersion associated to the disorder of the flow field
is dominant with a constant value of reached at high P\'eclet numbers.
The minimum dispersivity is slightly higher than in homogeneous nonconsolidated
packings of small grains, likely due heterogeneities resulting from wall
effects. In a disordered packing with the same beads as in the periodic
configuration, is up to 20 times lower than in the latter and varies as
with or (depending on the fluid viscosity).
A simple model accounting for this latter result is suggested.Comment: available online at
http://www.edpsciences.org/journal/index.cfm?edpsname=epjap&niv1=contents&niv2=archive