H001-08
Investigation of salt-precipitation processes in porous-media systems at the pore scale
Investigation of salt-precipitation processes in porous-media systems at the pore scale
Monday, 7 December 2020: 04:28
Virtual
Abstract:
The fundamental understanding of salt precipitation in porous media due to evaporation processes is important in different environmental and technical applications. For example salt precipitation in building materials generates stresses, which can lead to weathering and damage of constructions and cultural monuments. The salinization of soil in arid and semi-arid zones and the resulting reduction of crop yield is a further challenge.
During the evaporation of a salt solution, the salt concentration increases at the evaporation front and solid precipitates in the porous media when the solubility limit is exceeded. Here, many process controlling properties operate on the pore scale, such as the spatially varying salt concentration and the modification of pore space due to pore clogging.
To investigate these pore-scale processes, experiments were conducted at the microCT imaging facility at Oregon State University. A column filled with glass beads and potassium-iodide solution was scanned after several periods of evaporation at the column top using X-ray micro-tomography. From those images, the distribution of the brine and air phases as well as the location of precipitated solid salt, can be determined and analyzed. Additionally, the temporal development of the salt-concentration distribution in the brine phase is quantified with help of a concentration calibration. In combination with temperature and relative humidity measurements in the ambient air, this data set enables a very detailed analysis of the pore-scale transport and precipitation processes in porous media controlled by evaporation.
The findings of these experiments are used to develop and improve a numerical model which is able to represent these relevant pore-scale processes during salt-precipitation in porous-media using a pore-network model. With the comparison of the detailed experiment and simulation results, fundamental understanding of the processes at the pore scale during salt precipitation in porous media will be gained, and relevant processes will be determined.
During the evaporation of a salt solution, the salt concentration increases at the evaporation front and solid precipitates in the porous media when the solubility limit is exceeded. Here, many process controlling properties operate on the pore scale, such as the spatially varying salt concentration and the modification of pore space due to pore clogging.
To investigate these pore-scale processes, experiments were conducted at the microCT imaging facility at Oregon State University. A column filled with glass beads and potassium-iodide solution was scanned after several periods of evaporation at the column top using X-ray micro-tomography. From those images, the distribution of the brine and air phases as well as the location of precipitated solid salt, can be determined and analyzed. Additionally, the temporal development of the salt-concentration distribution in the brine phase is quantified with help of a concentration calibration. In combination with temperature and relative humidity measurements in the ambient air, this data set enables a very detailed analysis of the pore-scale transport and precipitation processes in porous media controlled by evaporation.
The findings of these experiments are used to develop and improve a numerical model which is able to represent these relevant pore-scale processes during salt-precipitation in porous-media using a pore-network model. With the comparison of the detailed experiment and simulation results, fundamental understanding of the processes at the pore scale during salt precipitation in porous media will be gained, and relevant processes will be determined.