longitudinal dispersion in nonuniform isotropic porous media

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homogeneous packing is not to be expected in general. The highly
extended breakthrough tails found experimentally are thought to be a
result of nonideal packing. A quantitative model of this process is
needed, since in some cases the residual concentrations in the tail are
important. Methods for determining the effective length and volume
scales of the diffusion limited regions are needed. Further
experiments are needed to test sands having different values of cr •
g
2. Many problems concerning transport phenomena in the natural
environment must deal with large-scale, radical heterogeneity in the
permeability as well as adsorption and chemical reactions. For
regional scale problems, spatial heterogeneity in the permeability
dominates the macroscopic dispersion of contaminants. Although there
has been a large amount of work on this subject over the past 15 years,
there is still no consensus on the best way to deal with the problem.
The effects of adsorption, chemical reaction, and biodegradation can
also be extremely important.
3. A permeability model is needed for the purposes of understanding
transport phenomena based on the grain scale characteristics of the
medium. The results of this research indicate a deterministic network
model may be appropriate. On the other hand, empirical observations
may show equation (3.11) is satisfactory. A theoretical basis for the
permeability in terms of a capillary tube network model would provide a
better understanding of the flow distribution in nonuniform porous
media.