New indirect estimation technique for the determination of the moisture diffusivity from transient moisture content profiles measured by means of X-ray radiography

摘要

The liquid water diffusivity is determined from transient moisture content profiles measured by means of X-ray radiography in a free water uptake experiment. In order to be able to apply the simplified onephase water diffusion approach to the wetting process, the concept of the boundary moisture content is introduced, which reproduces the measured liquid water transport both in transmission zone and steep wetting front. The boundary moisture content is considered as a parameter to be indirectly determined. We found that the classical direct method to determine the diffusivity: i.e. the Boltzmann transformation, results in a non-unique determination of the boundary moisture content and of the diffusivity at high moisture content. An indirect identification method is proposed based on a cubic spline parametric description of the diffusivity. The method was found to show a small increase in the (lack of) closeness-of-fit compared to the direct method, but the identification of the boundary moisture content and the diffusivity at higher moisture content remains unique.