Hydrodynamic dispersion during absorption in a fine sand: 2. The constant flux case

Abstract

The conclusions of an earlier paper involving hydrodynamic dispersion during absorption in a fine sand under constant concentration conditions are discussed in relation to the support they provide for the concept of a velocity dependent dispersion coefficient. The present study analyzes the more exacting constant flux case using influent boundary fluxes of water ranging from 3.28 × 10−7 ms−1 to 1.05 × 10−5 ms−1. These values allow the ratio of the mechanical dispersion component of the dispersion coefficient to the molecular diffusion component to vary from 0.43 to 5.81. For all cases, computer‐based numerical solutions are compared with experimental results using reduced space and time variables in the presentation of the data. It is observed that the bandwidth of the scatter of the experimental data is generally greater than the spread of the computed concentration profiles. In keeping with the constant concentration results, this suggests that the form of the experimental data is not inconsistent with the concept of a hydrodynamic dispersion coefficient which is velocity dependent. In all cases a dispersion length of 0.0001 m was used.