3GR - Géosciences Rennes (Bâtiment 15 - Université de Rennes 1 - Campus de Beaulieu -263 Av du général Leclerc- CS 74205 - 35042 Rennes Cedex - France - France)
Abstract : We investigate how diffusion-limited mixing of a layered solute concentration distribution within a porous medium impacts bulk electrical conductivity. To do so, we perform a milli-fluidic tracer test by injecting a fluorescent and electrically conductive tracer in a quasi two-dimensional (2D) water-saturated porous medium. High resolution optical-and geoelectrical monitoring of the tracer is achieved by using a fluorimetry technique and equipping the flow cell with a resistivity meter, respectively. We find that optical and geoelectrical outputs can be related by a temporal re-scaling that accounts for the different diffusion rates of the optical and electrical tracers. Mixing-driven perturbations of the electrical equipotential field lines cause apparent electrical conductivity time-series, measured perpendicularly to the layering, to peak at times that are in agreement with the diffusion transport timescale associated with the layer width. Numerical simulations highlight high sensitivity of such electrical data to the layers' degree of mixing and their distance to the injection electrodes. Furthermore, the electrical data correlate well with time-series of two commonly used solute mixing descriptors: the concentration variance and the scalar dissipation rate.
https://hal-insu.archives-ouvertes.fr/insu-03234565 Contributor : Isabelle DubigeonConnect in order to contact the contributor Submitted on : Tuesday, May 25, 2021 - 1:34:26 PM Last modification on : Friday, May 20, 2022 - 11:36:47 AM Long-term archiving on: : Thursday, August 26, 2021 - 7:36:55 PM
Alejandro Fernandez Visentini, Pietro de Anna, Damien Jougnot, Tanguy Le Borgne, Yves Méheust, et al.. Electrical Signatures of Diffusion-Limited Mixing: Insights from a Milli-fluidic Tracer Experiment. Transport in Porous Media, Springer Verlag, In press, ⟨10.1007/s11242-021-01607-0⟩. ⟨insu-03234565⟩