Methane concentration at heading faces with auxiliary ventilation

Three-dimensional airflow velocities at a heading face by a forcing or exhausting auxiliary ventilation system were measured in an actual size model gallery and in an actual mine. There were several stagnated regions near the roof corner, which might have danger of methane accumulation. Airflow velocities by an exhausting system were much smaller than that by a forcing system. The airflow and methane concentrations by a forcing, exhausting, or combined system were examined using a visualization technique by laser light in a reduced scale model. Water was used instead of air and very fine bubbles generated by electrolysis were employed as tracer. The behavior of the bubbles in water is similar to that of methane in the air. Accumulation of bubbles was observed at the roof corner of the face, which corresponds to the region, that the airflow stagnation was observed in the previous actual size model experiment. The optimal airflow rate through a forcing and exhaust duct and duct end locations to reduce hazard of methane accumulation were investigated for the combined system of ventilation. Experiments on methane accumulation using real methane in the air were also conducted in other reduced scale model.