Abstract
This study examines the evolution law of the coal temperature field under low-temperature freezing conditions. The temperature inside coal samples with different water contents was measured in real-time at several measurement points in different locations inside the sample under the condition of low-temperature medium (liquid nitrogen) freezing. The temperature change curve was then used to analyse the laws of temperature propagation and the movement of the freezing front of the coal, which revealed the mechanism of internal water migration in the coal under low-temperature freezing conditions. The results indicate that the greater the water content of the coal sample, the greater the temperature propagation rate. The reasons for this are the phase change of ice and water inside the coal during the freezing process; the increase in the contact area of the ice and coal matrix caused by the volume expansion; and the joint action of the two. The process of the movement of the freezing front is due to the greater adsorption force of the ice lens than that of the coal matrix. Thus, the water molecules adsorbed in the unfrozen area of the coal matrix migrate towards the freezing front and form a new ice lens. Considering the temperature gradient and water content of the coal samples, Darcy’s permeation equation and water migration equation for the inside of the coal under freezing conditions were derived, and the segregation potential and matrix potential were analysed. The obtained theoretical and experimental results were found to be consistent. The higher the water content of the coal samples, the smaller the matrix potential for the hindrance of water migration. Furthermore, the larger the temperature gradient, the larger the segregation potential, and the faster the water migration rate.
Highlights
The thermal effect of the freezing of rock via ambient temperatures has long been a popular issue in rock thermodynamic theory and engineering research
This study focuses on the evolution of the temperature field of the coal under low-temperature freezing conditions based on laboratory tests, and the water content and the distance of the measurement point inside the coal from the cold source are considered as variables
Water will phase into ice when in contact with a cold source, and the thermal conductivity of ice and water differ significantly; moisture is an important factor in the propagation of temperature within the coal rock mass
Summary
The thermal effect of the freezing of rock via ambient temperatures has long been a popular issue in rock thermodynamic theory and engineering research. Geotechnical construction in cold regions is currently on the rise, e.g., the construction of bridges, tunnelling, mining, the cryogenic geological storage of liquefied natural gas and liquefied petroleum gas, and construction by the freezing method, all of which subject the surrounding rock to periodic or long-term freezing at low temperatures. From an engineering perspective, the study of the temperature field evolution of coal bodies under low-temperature freezing conditions is of great significance for engineering construction in cold regions. The migration of unfrozen water from the coal rock to the frozen surface that occurs during the freezing process produces freezing and deformation, which cause hazards to foundation works, Int. J.
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