The core-tube method is a common method to measure the
coal seam
gas content (CSGC). However, cutting heat and friction heat will be
generated in the core-tube coring process, which will increase the
coal core temperature and the coal core gas loss, thus resulting in
a large error in the determination of the gas content. The accuracy
of the gas content determination is closely related to the temperature
variation of coal core during core-taking. Based on this, the team
developed the “thermal effect simulation device of coal core
in the core-taking process” and carried out the temperature
change test experiment of the coal core in the core-taking process
under different conditions. The results show that the temperature
variation of the coal core during the core-taking process shows four
stages: constant temperature, rapid temperature rise, slow temperature
rise, and temperature drop. The temperature rise rate, temperature
rise duration, and temperature rise peak of the coal core increase
with the increase in rotate speed, coal strength, friction area, and
frictional load. In the axial direction, the closer to the upper end
of the core pipe, the higher the core temperature. In the radial direction,
the closer the core is to the wall of the core pipe, the higher the
core temperature is. Under the influence of cutting heat and friction
heat in the process of core-taking, the maximum heating rate of the
core-taking tube wall within 8 min is 20 °C/min, the peak temperature
is 158.4 °C, the average temperature of the wall is above 100
°C, and the average temperature rise of the coal core reaches
55.7 °C. Within 60 min, the average temperature of the coal core
remained above 50 °C. The order of influence of coal core temperature
from large to small is as follows: rotate speed, frictional load,
friction area, and coal strength. It can provide a reference for accurately
determining CSGC using the core-tube method or designing a coring
device to eliminate or reduce the thermal effect during coring.