Experimental study on the migration and expansion of liquid nitrogen in loose media with different dip angles

Abstract

ABSTRACT The goaf is the main disaster area for natural fires in mines, and liquid nitrogen has become an essential medium for fire prevention in goafs due to its excellent cooling and inerting properties.At present, there is no in-depth research on the transport and vaporization of liquid nitrogen after injection into the goaf, and it is impossible to quantitatively evaluate the cooling inerting effect after liquid nitrogen injection. To address the above problems, this project proposes to carry out the following research: to study the effects of different inclination angles on the transport and vaporization of liquid nitrogen and temperature distribution in the loose medium in confined space by monitoring the temperature field changes during the pressure injection of liquid nitrogen in the loose medium in confined space.The results show that the temperature field distribution is very uneven after liquid nitrogen is injected into the loose medium in the restricted space.It is found that the vaporization rate of liquid nitrogen decreases with the increase of diffusion time and diffusion area, and the instantaneous vaporization rate of liquid nitrogen decreases with the larger inclination angle under the same injection position. Compared with the horizontal state, the maximum vaporization rate decreased 84.79% when the maximum inclination angle was 15°, which indicates that the vaporization rate was greatly affected by the inclination angle of the surface. In the vertical direction of the experimental box, the cooling area of liquid nitrogen in the experimental box is mainly concentrated within 0.05 m height from the bottom of the experimental box, and the changes of the “cooling restricted zone” after liquid nitrogen injection into the goaf are further explained during the experiment.It is found that the “cooling restricted zone” mainly exists in the upper part of the goaf, under the inclined condition, and the area increases with the increase of the inclination angle, so the increase of the angle is not conducive to the effective cooling effect of liquid nitrogen.The research results of the project will help to improve the theory of liquid nitrogen fire prevention in mines and provide theoretical support for the fire prevention technology of liquid nitrogen direct injection in goafs.