School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo 454003, China.
Collaborative Innovation Center of Coal Work Safety and Clean High Efficiency Utilization, Henan Polytechnic University, Jiacozuo 454003, China.
Int J Environ Res Public Health. 2021 Dec 14;18(24):13188. doi: 10.3390/ijerph182413188.
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.
本研究考察了低温冻结条件下煤温度场的演化规律。在低温介质（液氮）冻结条件下，对不同含水量的煤样在不同位置的几个测量点进行实时测量，得到煤样内部温度随时间的变化曲线，分析了温度传播规律和冻结锋面的移动规律，揭示了低温冻结条件下煤内部水分迁移的机制。结果表明，煤样含水量越大，温度传播速度越快。其原因是煤体冻结过程中冰和水的相变、冰和煤基质接触面积因体积膨胀而增大，以及两者的共同作用。冻结锋面的移动过程是由于冰透镜对煤基质的吸附力大于煤基质本身。因此，煤基质未冻结区中吸附的水分子向冻结锋面迁移并形成新的冰透镜。考虑到煤样的温度梯度和含水量，推导出了低温冻结条件下煤内部的达西渗透方程和水迁移方程，并对分离势和基质势进行了分析。理论和实验结果一致。煤样含水量越高，对水迁移的基质势阻碍越小。此外，温度梯度越大，分离势越大，水迁移速率越快。
