Spatially resolved velocity profiles and spatially nonresolved velocit
y distributions of steady flow in a tube and bead packs were measured.
Two different NMR experiments were used to measure velocity distribut
ions. In one, the velocity histogram was calculated from spatially res
olved velocity phase encoded images acquired in a 6 mm bead pack. In t
he other, a Fourier how method was used to measure the velocity distri
bution directly in a 0.25 mm bead pack. Axial velocity profiles in the
pore space of the 6 mm bead pack at Reynolds numbers of 14.9, 29.9, a
nd 44.8 proved to be roughly parabolic, with maxima near the pore cent
ers. Both NMR methods yielded the same dimensionless velocity distribu
tions that contain negative as well as positive velocity components. T
he velocity distribution function derived from a bundle-of-tubes-model
accounts for the positive part of the velocity distribution. (C) 1996
American Institute of Physics.