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Visualisation of flow processes in packed beds with NMR imaging: determination of the local porosity, velocity vector and local dispersion coefficients

Authors
Journal
Chemical Engineering and Processing Process Intensification
0255-2701
Publisher
Elsevier
Publication Date
Volume
41
Issue
7
Identifiers
DOI: 10.1016/s0255-2701(01)00185-4
Keywords
  • Packed Bed
  • Tube Reactor
  • Cylinder-Bundle
  • Nmr Imaging (Mri)
  • Flow Imaging
  • Local Porosity
  • Velocity And Dispersion Coefficient
Disciplines
  • Mathematics

Abstract

Abstract Magnetic resonance imaging (MRI) techniques are used to visualise flow phenomena within packed beds. In order to develop the most complex structure of the packed beds step by step from simpler geometric structures firstly the flow in a tube with one cylinder and a bundle of ten cylinders is investigated. It is possible to determine the three-dimensional (3-D) porosity and velocity distribution within the packing. The flow processes in the inlet region (i.e. transition from the tube without installations to the packing), in the packing and at the outlet of the packing can clearly be distinguished. The expected high porosity at the wall, the oscillating transition to the mean porosity in the interior of the tube and the corresponding wall effect on the flow distribution due to the radial distribution of the porosity could be detected. Furthermore, back flow, stagnant volumes and regions with high gradients of single velocity components can be detected. Axial and radial dispersion coefficients, porosity and velocity distributions, averaged in angular φ and axial direction z, can be derived from the nuclear magnetic resonance (NMR) data. This information is necessary for modelling the structure and the flow within a packed bed and for verifying theoretical predictions with regard to the distribution of the porosity and the velocity. Vector representation of the velocity field can be obtained.

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