A Visualization Study of Mechanical Dispersion in Porous Media

ABSTRACT

A visualization technique using fluorescein sodium has been developed for the study of mechanical dispersion within fluid-saturated porous media. The technique is based on the correlation between the color intensity of blue and the concentration of fluorescein sodium. Having constructed the calibration curve to relate the blue intensity and the concentration, the measurements were made for the parallel streams of different concentration within the shallow channel where small rectangular blocks were arranged in a periodical fashion. The dilute fluorescein sodium solution was supplied from the central slot of the inlet section to form the central stream, at the same velocity as the adjacent water streams. The solution diffuses into these water streams as the central stream moves through the channel. The color intensity within the field of interest was monitored and then processed to obtain the concentration distribution. Numerical computation results based on the macroscopic mass transfer equation with an adjustable dispersion coefficient was compared against the concentration obtained from the visualization, so as to determine the dispersion coefficient, which provides the best agreement between the numerical and experimental results.

Keywords: