| Research Abstract |
The relation between the mass transport rate and the spatial distribution of retardation coefficient, R_d, has been examined.
To express the distribution of retardation effects, this study used the two-dimensional packed bed with two kinds of silica, i.e., silica sand and silica gel particles. The solution of Eu(III) as a tracer was injected into the packed bed. Based on the experiment results of the breakthrough curve, this study proposed two-dimensional mathematical model to explain the retardation effects with two-dimensional advection-dispersion.
Using the calculated breakthrough curves, next, we focused on the peak height and its arrival time. To compare them easily, the dimensionless mean residence time was always set at unity. In the results, when the R_d values were distributed perpendicular to the flow direction, the peak height and its arrival time strongly depended on the R_d distribution. This study, for simplicity, considered two kinds of R_d layers, assuming that the small R_d and the large were arranged parallel to one another. The smaller the alternation frequency of the layers became, the higher peak and the shorter arrival-time the breakthrough curve showed. In contrast, as the frequency was large enough, the peak-arrival time almost agreed with the homogeneous case.
Further, this study confirmed that the variation of the skewness of R_d had no appreciable influence on the whole mass transport rate. When the 2-D distribution of R_d was described by, e.g., log-normal distribution, the average mass transport rates showed agreement with those on the other probability density functions defined by the same set of the arithmetic mean and the standard deviation of R_d. These tendencies mentioned above were confirmed in the range of Peclet number from 10 to 10^2 for the dimensionless standard deviation at least up to around 1.
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