Three-dimensional structure and local velocity measurement in porous media by magnetic mesonance imaging

For understanding of heat and mass transpon in porous system, it is necessary to observe the pore geometries and to measure the local velocity profiles in the interstitial regions at the microscopic scale. Using magnetic resonance imaging (MRI) which has the advantage of noninvasive and nonoptical measurement, analysis of pore structure and velocity measurement of interstitial flow through water-saturated porous media have been performed experimentally. Twe samples consisted of crashed glass particles and spherical beads in the typical diameter range of 2 to 5 mm were used as porous media. Three-dimensional pore images of the porous media were reconstructed from obtained multi-slice images of water-saturated porous medium. And then porosity and pore size distributions as pore structure parameters were determined by image analysis based on the images. Using spin-echo sequence with tagging pulses for flow visualization, three-dimensional velocity vectors of steady-state flow in the interstitial regions at the pore scale have been measured. The effect of mean flow velocity through the porous medium, which is calculated from flow rate, section area and the mean porosity of the porous medium, on the flow structure has been investigated in range of the mean flow velocity from 3.84 mm/s to 13.2 mm/s. The obtained vector maps show nonuniform flow depending on mean flow velocity and the reversed flow generated due to the pore geometry and the network structure. The frequency distributions of the flow velocities analyzed by statistical treatment spread widely and are influenced sensitively by the pore geometry in the porous media.