Water and Salt Migration with Phase Change in Saline Soil during Freezing and Thawing Processes
Water and salt transfer coupled with phase change may cause serious damage to engineering structures in saline soil regions. In this study, the migration of water and salt in silty clay collected from the Qinghai‐Tibet Plateau is explored experimentally and numerically during freezing and thawing processes. The results revealed that there are significant differences in the variations of liquid water content and solution concentration for different initial salt contents, due to salt crystallization and dissolution. The temperature‐induced water migration is determined by the soil properties, which can be well explained by the thermodynamics of mass transfer. The amount of salt migrated upward during cooling is slightly larger than that transported downward in the warming period, implying that salt may be accumulated in the surface soil after a large number of circulations and finally result in soil salinization.
Study on phase changes of ice and salt in saline soils
Abstract The occurrence of different ice and salt phases in saline soils may result in severe failure in engineering practice. Therefore, studying the phase changes of these two components may improve the understanding of saline soils. Through a series of cooling experiments on sulfate saline soils, the internal temperature variation of soils is obtained to study the rule of salt crystallization and the effect of salt on liquid water content. Based on the thermodynamic principle, the heat transfer equation is expressed considering the phase changes of ice and salt, and the control volume approach is applied to discretize the differential equation of heat transfer. Combined with the internal temperature curve of the soils, the discrete equations allow the calculation of ice porosity variation, salt crystal porosity, and unfrozen water content in saline soils. Additionally, the equations provide a useful general criterion for salt crystallization at different temperatures. Experimental and theoretical results confirm that unfrozen water content in saline soils decreases as the salt content increases, and that liquid water content is lower in salt-free soils. In addition, the concentration of salt solution in soils with low salt content increases owing to the phase change between water and ice; salt crystallization can only occur if the concentration reaches 20% at a negative temperature.
Energy
Energy is often defined as the ability to do work. There are many forms of energy. A few examples include; Gravitational energy, Kinetic energy (energy of motion), Thermal energy (heat energy), Potential energy. Potential energy is the energy something has based on its position in the universe. A stretched elastic band has potential energy. A rock held up in the air has potential energy based on its position.