Pulsed Gradient NMR Measurements and Numerical Simulation of Flow Velocity Distribution in Sphere Packings.
Pulsed Gradient NMR Measurements and Numerical
Simulation of Flow Velocity Distribution in Sphere
Packings.
(827 K)
Lebon, L.; Oger, L.; Leblond, J.; Hulin, J. P.; Martys,
N. S.; Schwartz, L. M.
Physics of Fluids, Vol. 8, No. 2, 293-301, February
1996.
Keywords:
sphere packings; velocity distribution; porous media;
water; experiments
Abstract:
The displacement of water molecules associated with the
flow of water inside a nonconsolidated packing of 800 mm
OD glass spheres has been measured by a pulsed gradient
NMR technique. Using a stimulated spin-echo sequence,
mean displacements of up to 300 mm corresponding to
measurement times of up to 200 ms can be analyzed. The
measurement can be quantitatively calibrated using the
pure molecular self-diffusion of water at zero flow
conditions. For molecular displacements much smaller
than the pore size, the distribution of the flow
velocity component along the mean flow direction is
determined at Reynolds numbers high enough so that
longitudinal molecular diffusion is negligible. An
exponential decay of the probability distribution of the
displacements is observed at large distances. The
results are very similar to those obtained by numerical
solution of the Stokes equation in random sphere
packings. At longer displacement distances, a secondary
peak of the displacement distribution is observed. It
is interpreted as the first step toward the transition
toward classical dispersion at displacements much larger
than the pore size. The influence of molecular
diffusion and of the heterogeneities of the magnetic
permeability also are discussed.
