An experimental system for liquid nitrogen soaking and real-time temperature measurement was designed and implemented to\ninvestigate the characteristics of temperature field changes in coal under liquid nitrogen soaking. Then, the heat conduction law of\nthe coal in the process of liquid nitrogen soaking and room temperature recovery for dry and water-saturated coal were examined.\nThe microstructure characteristics of the coal before and after liquid nitrogen soaking were analyzed with nuclear magnetic\nresonance (NMR) technology. Theresults showed that, during the liquid nitrogen cold soaking process, the heat transfer law of the\ndry and water-saturated coal samples exhibited a notable three-stage distribution. For the room temperature recovery process, the\ndry and water-saturated coal samples exhibited rapid heating characteristics, and the cooling rate gradually decreased to zero.\nNMR test results indicated that the liquid nitrogen soaking increased the number of micro and small pores in the coal. Thermal\nstress analysis revealed that the thermal stress generated by the dry coal was larger than that produced by the saturated coal, and\nthe damage was primarily caused by thermal stress. However, the permeability of the saturated coal was better than that of the dry\ncoal. The damage on the saturated coal was caused by the volume expansion of pores and fissures caused by water-ice\nphase transition.
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