Estimating Solute Dispersion Coefficients in Porous Media at Low Pore Water Velocities

Abstract

The relationship between solute dispersion coefficient (D mech ) and pore water velocity during chloride transport in porous media with different particle characteristics at low pore water velocities (u < 1 cm min −1 ), relevant for ground water flow conditions, was investigated. Data for 29 porous media with very different particle shapes (ranging from almost spherical to very angular) and particle sizes (0.088-12 mm) at different velocities (340 breakthrough curves) were used in the analyses. The analysis showed that D mech at low u is significantly different from that at higher u. Whereas the u -D mech relationship generally can be assumed linear at higher u (based on observations in earlier studies), the data presented in this study clearly show that this is not the case at low u. The results further indicated that D mech at low u is strongly related to porous medium particle shape and to some degree also to medium particle size range and mean particle diameter. As the current knowledge about dispersion at low u and its dependency on porous medium properties is very limited, the results obtained in this study represent a significant addition to this understanding. A set of expressions for predicting D mech at low u from medium properties was developed. These expressions yield good accuracy across all 29 media, thus providing a means for predicting dispersion at low u across a very wide range of media.

Effects of Velocity and Permeability on Tracer Dispersion in Porous Media

“…These figures confirm the trends observed in Tables 3 and 4. The results of this work reveal a linear relationship between the dispersion coefficient and fluid velocity as shown in Equations ( 1) and (2), inconsistent with the previous findings of the nonlinear relationship [35][36][37][38]. The cause of this difference can be attributed to the grain shape and fluid velocity.…”

“…The longitudinal dispersion coefficient D L does not vary linearly with water velocity Pugliese and Poulsen [36] Measuring the dispersion coefficient in a series of porous media with different grain sizes and shapes…”

“…The cause of this difference can be attributed to the grain shape and fluid velocity. As Pugliese and Poulsen [36] demonstrated, the closer a particle is to a spherical shape, the more significant the nonlinear relationship between the dispersion coefficient and the velocity of water flow. As the grain diameters in core samples are in the scale of micrometers and the grain shape is close to spherical, it is reasonable to approximate the grains as spheres and obtain a linear relationship.…”

Gas Dispersion Coefficient Test System and Dimensionless Inversion Method for Porous Media

“…They found that the dispersion coefficient continued to decline when the density difference of the displaced fluid increased or the viscosity ratio decreased. Pugliese and Poulsen 33 used a series of particles with different shapes and sizes as porous media to conduct experimental research on fluid dispersion. The results show that the closer the porous media particles are to the sphere, the more obvious the linear relationship between the dispersion coefficient and water flow velocity is.…”