Title:
Water transport through hygroscopic porous materials (paper, wood, textiles, fiber panels): a subtle three-phase flow Abstract:
Most bio-based materials, such as paper, natural textiles, sponges, wood or plants, fiber panels for insulation, are porous systems through which water transfers play an essential role in the applications. A specificity of these materials is that they are also hygroscopic: they can absorb huge amounts of water, typically up to about 25% of their dry mass, from ambient vapor, in the form of bound water confined at a nanoscale in the amorphous regions of the cellulose structure, a bound water at the origin of the significant swelling of these materials. Remarkably, this bound water is also strongly mobile inside the solid phase. For example, the bound water contained in a cellulose fiber stack whose porosity has been filled with oil may be extracted by drying, proving that it is transported inside the fibers throughout the network. Moreover, the corresponding transport diffusion coefficient of bound water appears to be rather large, in the order of the self-diffusion coefficient of (free) water. These characteristics imply that, more generally, in hygroscopic porous materials, water can be transported through the system in three different phases, i.e., vapor, free water and bound water, which are strongly coupled via sorption or desorption processes. Finally, the coupling between some or all of these different processes leads to unexpected physical characteristics.
The original implications are illustrated by the long-term evolution of an aqueous droplet, possibly containing particles such as pigments and viruses or solute such as ions and polymers, and reaching the surface of a cellulosic sample. It is generally considered that such a droplet somewhat spreads, penetrates the structure, stabilizes and eventually dries. In fact, it may be shown from NMR (nuclear magnetic resonance) relaxometry and MRI (magnetic resonance imaging) that, instead of drying, the water is absorbed as bound water and diffuses throughout the entire structure. Thus, the initial (free) water rapidly disappears from the porosity, while the non-absorbed solute or particles remain stuck to the solid surfaces in the initial region of liquid penetration.
Another original effect if the imbibition of wood with water. As observed with NMR and MRI, the standard liquid water penetration thanks to capillary effects through vessels is slowed down by several orders of magnitude of time because the structure does not allow the invasion of free water in the regions where cell walls are not saturated with bound water. Bio:
Philippe Coussot is a senior researcher in the Rheophysics and Porous Media department of Laboratoire Navier (Univ. Gustave Eiffel – CNRS – Ecole des PontsParisTech). After a first career stage on the hydraulics of mudflows and debris flows, he focused on the rheology of pastes and suspensions and, in a second step, on transfers (drying, imbibition, colloid transport) in porous media, with the help of NMR and MRI. His main current research concerns the hygrothermal behavior of bio-based construction and textile materials, in particular within the frame of the ERC Advanced Grant PHYSBIOMAT. He published Mudflow Rheology and Dynamics (Balkema, 1997), Rheometry of pastes, suspensions and granular materials (Wiley, 2005), and Rheophysics (Springer, 2014), and received the Silver Medal from CNRS (2015), the Weissenberg Award from the European Society of Rheology (2017), and the Medal for Porous Media Research from Interpore (2023). |
Title:
The Influence of Multiple Scales in Fractured Media on Flow and Transport Properties Abstract:
In low-permeability fractured media, such as granites and shales, flow and the associated transport of dissolved solutes is controlled primarily by fractures embedded within the rock matrix. The geometry of individual fractures, size and aperture, as well as the network structure determine the structure of the fluid flow field. However, the relevant lengths scales within a fracture network range several orders of magnitude and it is unclear which features of the network influence which flow and transport properties. One tool to investigate the interplay and influence of these multiple scales are discrete fracture network (DFN) models. In this talk, I’ll discuss recent studies that use high-fidelity DFN models that attempt to link flow and transport attributes to physical structures of a fracture network ranging in-fracture aperture variability to network-scale connectivity. Bio:
Dr. Jeffrey Hyman is a staff scientist in the Earth and Environmental Sciences Division at Los Alamos National Laboratory. He received his PhD in Applied Mathematics from the University of Arizona in 2014 with a PhD Minor in Hydrology and Water Resources. His research focuses on integrating applied mathematics with the geosciences to advance our understanding of coupled subsurface processes in fractured media. He is an Affiliate Faculty in the department of Geology and Geological Engineering at Colorado School of Mines and the director of the Advanced Computational Geosciences Initiative (ACGI) at Los Alamos National Laboratory. He has published over 100 peer-reviewed articles. Dr. Hyman is the principal developer of dfnWorks (2017 R&D 100 Winner) a leading modeling suite for three-dimensional discrete fracture network simulations. |
