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@ARTICLE{Herrmann:9061,
      author       = {Herrmann, K. H. and Pohlmeier, A. and Gembris, D. and
                      Vereecken, H.},
      title        = {{T}hree-dimensional imaging of pore water diffusion and
                      motion in porous media by nuclear magnetic resonance
                      imaging},
      journal      = {Journal of hydrology},
      volume       = {267},
      issn         = {0022-1694},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier},
      reportid     = {PreJuSER-9061},
      pages        = {244 - 257},
      year         = {2002},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {We report on the use of a pulsed gradient spin-echo imaging
                      sequence for the three-dimensional (3D) imaging of water
                      transport properties in two porous media: 2 mm glass-beads
                      and 0.15 turn quartz-sand mixed with 2 turn glass-beads. In
                      contrast to tracer methods, which monitor the tracer motion
                      by its effect on the signal relaxation of H-1, this sequence
                      measures the echo signal intensity I-0 without and I with
                      applied diffusion gradient, respectively. For the wide-pore
                      glass-bead system, the intensity loss is controlled by
                      nearly free self-diffusion in the pores. A mean apparent
                      diffusion coefficient is calculated from the ratio ln(I-0/I)
                      as <D-loc> = 1.9 x 10(-9) m(2) s(-1), which is slightly
                      lower than that of free water (D = 2.3 x 10(-9) m(2) s(-1)).
                      Increasing the mean pore flow velocity from 0 to 0.14 mm
                      s(-1) results in a linear increase of <D-loc> to 2.3 x
                      10(-9) m(2) s(-1), caused by mechanical dispersion. The
                      spatial distribution is of the log-normal type, where the
                      width increases with increasing pore velocity. Correlation
                      lengths are also calculated.For the fine porous medium,
                      frequent contacts of the water molecules with the pore
                      boundaries lead to a significant decrease of I-0 by
                      increased T-2 relaxation. The resulting ratio of the signal
                      intensities ln(I-0/I) is then smaller than expected for pure
                      diffusion, which is caused by the restricted diffusion in
                      the fine pore system. The spatial distribution (normal) is
                      broader than for the glass-bead system and the mean local
                      apparent diffusion coefficient is calculated as 1 x 10(-9)
                      m(2) s(-1), a dependence on the pore flow velocity could not
                      be detected.For the glass-bead system, the 3D image clearly
                      shows regions of increased dispersivity $(50\%$ greater than
                      the D-loc), caused by packing errors, leading to
                      preferential flow. This macroscopic effect on the column
                      scale is quantified by a numerical simulation of tracer
                      transport, based on the 3D diffusion coefficient field,
                      assuming a linear relation to local velocities. From this
                      simulation, the effective dispersion coefficient is obtained
                      for the column scale (D-eff = 130 x 10(-9) m(2) s(-1)),
                      which is comparable to that obtained from classical
                      break-through curves with tracer substances. (C) 2002
                      Published by Elsevier Science B.V.},
      keywords     = {J (WoSType)},
      cin          = {IME / ICG-IV},
      ddc          = {690},
      cid          = {I:(DE-Juel1)VDB54 / I:(DE-Juel1)VDB50},
      pnm          = {Biotechnologie},
      pid          = {G:(DE-Juel1)FUEK256},
      shelfmark    = {Engineering, Civil / Geosciences, Multidisciplinary / Water
                      Resources},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000178504900010},
      doi          = {10.1016/S0022-1694(02)00154-3},
      url          = {https://juser.fz-juelich.de/record/9061},
}