EXPERIMENTAL INVESTIGATION OF CHARACTERISTIC LENGTH SCALE IN PERIODICHETEROGENEOUS POROUS-MEDIA

An experimental investigation of scale-dependent dispersion in periodi c heterogeneous porous media was conducted. Models with two-, three- a nd four-layer periodic heterogeneities were constructed to investigate the effect of heterogeneity size on the scale-dependence of dispersio n. Longitudinal dispersion coefficients were determined as a function of column length by measuring the breakthrough of a continuous injecti on of potassium chloride tracer solution. Chloride ion concentration w as monitored by recording the millivolt potential of silver/silver chl oride electrodes placed at intervals along the length of the column. I n all three models, dispersion appeared to be scale dependent up to a distance of approximately 20-30 times the size of the repeated heterog eneity group (hydraulic unit). Because all three models suggested a si milar dependence, it was concluded that a medium with periodic heterog eneity may likely be characterized by the scale of its hydraulic unit.