Determination of the Moisture Characteristic from Freezing Experiments
Collaborators: M. Bittelli (Washington State University) and G. S. Campbell (Decagon Devices, Inc.)
The moisture characteristic is the relation between water content and water potential in a porous medium. Knowledge of the moisture characteristic is essential in many areas dealing with porous media, e.g., food, plant tissue, soils, sediments, and rocks. For example, water flow in soils and rocks depends on the moisture characteristic, and therefore scientists and engineers characterizing water flow rely on accurate data of the moisture characteristic. Currently, the moisture characteristic is cumbersome to measure. Present technology is time-consuming, and thus expensive, and often yields inaccurate results.
The biggest problem with current measurement techniques is that during the measurement procedures, water has to be sucked or pressed out of the samples, and is replaced with air. When samples are relatively dry, the hydraulic conductivity decreases by orders of magnitude and becomes extremely small. Equilibration times then become often prohibitively long. In addition, no single instrument exists that can determine the moisture characteristic over the entire domain of interest, different instruments have to be used to measure a complete moisture characteristic from wet to dry. We propose to develop an alternative technique to measure the moisture characteristic by freezing the porous media sample and determining the liquid water content by Time Domain Reflectometry (TDR). The ultimate goal of the project is to develop a laboratory-bench instrument that can measure the relation between liquid water content and water potential fast, accurately, and over the entire domain from wet to dry. The freezing technique has shown great potential to achieve this goal.
The specific objectives are (1) to develop and optimize an instrument to measure the freezing characteristic, i.e., the relation between temperature and unfrozen water content in a porous media, (2) to use thermodynamical theory to convert the freezing characteristic to the moisture characteristic, and (3) to optimize and test the developed instrument by comparison with conventional measurement techniques.
Publications
- Bittelli, M., M. Flury, and K. Roth, Use of dielectric spectroscopy to
estimate ice content in frozen porous media, Water Resour. Res., 40, W04212, doi:10.1029/2003WR002343, 2004.
- Bittelli, M., M. Flury, G. S. Campbell, and V. Schulz, Characterization of a spiral-shaped time domain reflectometry probe, Water Resour. Res., 40, W09205, doi:10.1029/2004WR003027, 2004.
- Bittelli, M., M. Flury, and G. S. Campbell, A thermo-dielectric analyzer to
measure the freezing and moisture characteristic of porous media,
Water Resour. Res., 39, doi:10.1029/2001WR000930,
2003.
Markus Flury 
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