NMR imaging of velocity profiles and velocity distributions in bead packs

Spatially resolved velocity profiles and spatially nonresolved velocity distributions of steady flow in a tube and bead packs were measured. Two different NMR experiments were used to measure velocity distributions. In one, the velocity histogram was calculated from spatially resolved velocity phase encoded images acquired in a 6 mm bead pack. In the other, a Fourier flow method was used to measure the velocity distribution 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, and 44.8 proved to be roughly parabolic, with maxima near the pore centers. Both NMR methods yielded the same dimensionless velocity distributions that contain negative as well as positive velocity components. The velocity distribution function derived from a bundle-of-tubes-model accounts for the positive part of the velocity distribution.