Experimental study of high concentrations of coal mine methane behavior in downward ventilated tilted roadways

The movement and distribution of methane in coalmine roadways are major issues relating to coalmine safety. Once high concentrations of methane accumulate in downward ventilated tilted roadways, the movement of methane can be very special. A 1/50 experimental model was constructed for the study on high concentrations of methane behavior in downward ventilated parallel roadways. This experiment measured gas concentrations in the upper and lower parts of the methane accumulating roadway and the wind speeds both in the methane accumulating roadway and in its parallel roadway The experimental results indicate that the methane draft pressure (the additional natural draft pressure due to the density difference of methane and air when high concentrations of methane accumulate in tilted roadways) could lead to airflow reversion in a downward ventilated roadway; methane may flow with the reversed airflow into the parallel roadway. The reversed methane that flows into the parallel roadway could generate a new methane draft pressure, which would oscillate airflow under certain conditions. According to the experimental results with parallel roadways of different windage, a larger windage of the parallel branch could ensure a relatively stable airflow, and a smooth methane discharge process. Through analysis by oscillation theory and the Archimedes number, it is concluded that the parallel roadway windage affects the methane draft pressure-caused airflow disorder by two aspects: (1) a larger windage deceases the amplitude of airflow oscillation and (2) a larger windage decreases the methane flown into the parallel branch, which, in turn, decreases the critical wind velocity for airflow reversion in the parallel roadway. The effect of windage is proved by a numerical simulation of Jiulishan Mine at the end of this paper.