Time domain reflectometry developments in soil science: II. Coaxial flow cell for measuring effluent electrical conductivity

Henrik H. Nissen, Paul A. Ferré, Per Moldrup

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Time Domain Reflectometry (TDR) is a recognized and widely used technique for measuring electrical conductivity (EC) and volumetric water content (θ) in porous media. The ability of TDR to measure both EC and θ is especially appealing in solute transport in variably saturated media. It is commonly assumed that TDR measurements are representative of the EC and θ in the horizontal plane in which the probe is located. The problem is that it is difficult to recognize heterogeneous solute transport with TDR, especially if it occurs outside the sample volume or in regions where the solute is giving little weight to the TDR-measured EC. To determine the presence of heterogeneous solute transport effectively, there is a need for a device to monitor the EC boundary conditions. In this study, a simple and easy-to-make coaxial flow cell is designed and tested for this purpose. The flow cell is made primarily of cheap, prefabricated, and readily available components, and the construction requires only a hacksaw and some welding skills. The idea is to make the effluent from a solute transport experiment pass through the coaxial flow cell, thereby obtaining a measure of the effluent EC. In addition to providing detailed information on the solute transport through the entire sample of porous medium, it will also detect, for example, bypass flow. A solute transport experiment was carried out in a PVC pipe packed with coarse silica sand under saturated conditions to calibrate the flow cell and to demonstrate its potential use. Step input breakthrough and breakdown functions were created using tap water and a KCl solution. Highly detailed measurements of EC in the effluent were obtained, from which solute transport parameters can easily be inferred.

Original languageEnglish (US)
Pages (from-to)84-89
Number of pages6
JournalSoil Science
Issue number2
StatePublished - Feb 1 2003


  • Coaxial flow cell
  • Electrical conductivity
  • Solute transport
  • Time domain reflectometry

ASJC Scopus subject areas

  • Soil Science


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