How does drying-driven crystalized salt influence the dynamics of water evaporation from porous media?

• Applicant: Professor Nima Shokri
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 497539130

Soil salinization, referring to excess accumulation of soluble salts in soil, has detrimental impacts on crops, animal and human health. It is one of the main land-degrading threats influencing soil fertility, stability, and bio-diversity leading to undesirable changes in the physical, chemical, and biological functions of the soil. Beyond soil, it has significant impacts on other processes such as the durability of building materials, preservation of pavements, and CO2 sequestration. Saline water evaporation is influenced by transport properties of the porous media, external conditions (e.g. wind, ambient temperature, and relative humidity), properties of the evaporating solution, and salt crystallization. During water evaporation from soil, solute is transported via capillary induced liquid flow, from the wet zone at the bottom to the evaporation surface. Simultaneously, diffusion tends to spread the solute homogeneously across the entire domain. The competition between upward advection and diffusion transport determines solute distribution throughout the soil. When advection dominates diffusion, solute in preferentially deposited close to the surface leading to gradual increase of its concentration. When salt concentration substantially exceeds the solubility limit, crystals will precipitate at soil surface. The crystals formed at the surface create complex, branching structures, which can substantially increase the surface area available for evaporation. How exactly the presence of the evolving evaporation-driven porous crystallized salt at the surface influences the evaporative water losses from soil under different boundary conditions is poorly understood. Detailed information about the complex coupling between flow and transport processes within porous media and the evolving crystallized salt at the surface is required for accurate prediction of water evaporation from soil otherwise our description of this process would reply on adjusting parameters. Without such knowledge, one may notably underestimate or overestimate water availability and evaporation from land surface which will influence several hydrologic processes. In this project, we plan to conduct a comprehensive multiscale numerical and experimental investigations to quantify the effects of the evolving evaporation-driven crystallized salt at the surface on the evaporative water loses from porous media. Within this context, we will utilize the state-of-art numerical and experimental tools such as molecular dynamics simulation, pore-network and continuum-scale modelling, synchrotron X-ray micro-tomography and customized laboratory experiments to achieve the objectives of this project. Such efforts will enable us to provide an accurate description of saline water evaporation which will place us in a stronger position to quantify soil water evaporation and land-atmosphere interactions.

• DFG Programme: Research Grants
• International Connection: USA
• Co-Investigator: Professor Dr.-Ing. Rainer Helmig
• Cooperation Partner: Professor Dr. Muhammad Sahimi