| Transverse dispersion in porous media has been identified as a key parameter in a variety of subsurface processes. It controls the dissolution rate of contaminant sources, the dilution of conservative solutes, the mixing of reacting solutes, and plays a decisive role in the decay of concentration fluctuations. Estimating the transverse dispersivity, a property of the porous medium, is necessary for assessing the hydrodynamic part of the transverse dispersion. This work presents a methodology and tracer experiments to measure the transverse dispersivity of homogeneous isotropic media using a cochlea, a spiral cavity like that of a nautilus shell, and a helix. The incentive is that the transport of a conservative tracer in a device with spiral flow motion results in a concentration breakthrough curve that is inversely related to the transverse dispersion parameters. By performing conservative-tracer experiments in a helix and a cochlea we can obtain experimental breakthrough curves. The flow field in the helix is complex and is solved numerically. In the cochlea the flow field is simpler and is solved analytically. The solution of the flow field is applied to particle-tracking random-walk simulation of solute transport which is used as forward model in a non-linear optimization method to determine the transverse dispersivity of the porous medium.; Estimates of the transverse dispersivity obtained for each experiment are presented and the relative advantages of each device, instrumentation, and methodology are discussed. The most noteworthy conclusions of this research are that the results from the two devices are in agreement and that the ratio of transverse dispersivity to longitudinal dispersivity that we estimate agrees with the higher ratios reported in the literature. |
