96 / 2021-09-28 19:43:16

Temperature field evolution and water migration law of coal under freezing condition

low-temperature freezing，temperature propagation，freezing front，Water migration，coal.

This study examines the evolution law of the coal temperature field under low-temperature freezing conditions. The temperature was measured in real-time at several measurement points in different locations inside the coal sample under low-temperature medium (liquid nitrogen) freezing. The temperature change curve was used to analyze the temperature propagation and freezing front movement law of coal with different moisture content, which revealed the mechanism of internal water migration in coal under low temperature freezing conditions. Results show that the greater the moisture content of the coal sample, the greater the temperature propagation rate. The reasons are the ice and water phase change inside the coal during the freezing process, the phase change volume expansion caused by the increase in the contact area of the ice and coal matrix, and the joint action of the two accelerated temperature propagation rates of the coal. The freezing process of the freezing front movement is due to the adsorption force of the ice lens than the adsorption force of the coal matrix. Thus, the water molecules adsorbed in the unfrozen area of the coal matrix migrate toward the freezing front and form a new ice lens. Under the consideration of temperature gradient and moisture content of coal samples, Darcy’s permeation equation and water migration equation inside the coal under freezing conditions were derived, and the segregation potential and matrix potential were analyzed. The obtained theoretical and experimental results were consistent. The larger the moisture content of coal samples, the smaller the matrix potential is for the hindrance of water migration. Furthermore, the larger the temperature gradient, the larger the segregation potential, and the faster the water migration rate.