Nowadays, the water jet technique has been more frequently used for coal bed methane stimulation. As the ultimate component of the water jet system, the nozzle has important influence on the rock breaking ability of water jet. To optimize the nozzle, a simplified model for impinging water jet was established. The effects of geometric structure (cylindrical, conical, and conical‐straight) and parameters (outlet diameter d, conical angle α, and length L) on the flow field of the impinging water jet are simulated through computational fluid dynamics software Fluent14.0. Besides, the effects of inlet pressure (Pin) and target distances (S) on the jet dynamics are also discussed based on the simulation results. The results show that the jet dynamic parameters including dynamic pressure, velocity, and impinging pressure vary with different nozzles. The jet dynamic parameters linearly increase with the inlet pressure, while they first increase then decrease with the increase in target distance. Additionally, the optimal nozzle designed based on the numerical simulation was used in the field test, and the results indicate that this technique can effectively improve the gas drainage efficiency.

Reliable ventilation is the cornerstone of safe production in coal mines, and accurate monitoring of ventilation parameters is the fundamental guarantee of ventilation technology decision‐making. To improve the accuracy of airflow velocity monitoring in coal mine roadways, theoretical analysis, numerical simulation, and field tests were utilized to study the distribution law of airflow velocity in typical roadway sections. First, the calculation model of position of mean airflow velocity line in rectangular and semicircular arch roadway is established based on Boussinesq theory and Pelant turbulence theory. Then, to verify the correctness of the theoretical model, 25 groups of numerical simulation tests were conducted by using COMSOL‐Multiphysics 3.5a software. The errors between theoretical analysis and numerical simulation are all less than 4%. In addition, the numerical results also show that the contour line of airflow velocity in roadway section is consistent with the shape of roadway section, and the isoline of airflow velocity is basically parallel to the roadway wall. In addition, the closer to the roadway wall, the denser the airflow velocity isoline, indicating that the airflow velocity gradient near the wall is larger. And the thickness of the boundary layer decreases with the increase of airflow inlet velocity. Finally, field tests have been conducted in Chongqing Research Institute and Sima Coal Mine to further verify the correctness of the calculation model and numerical simulation results. The measured distribution law of airflow velocity is consistent with the numerical simulation. And the errors between theoretical analysis and field tests are all less than 4%.

The ventilation system is an important component of the mine safety production system, which directly affects the mine production capacity and on-site safe and efficient production. Taking the air demand and ventilation capacity of the Xinyuan coal mine as the research object, the air demand of the coal mining face, excavation face, backup face, chamber, and other air consumption tunnels were analyzed and calculated. The ventilation capacity of the mine ventilation system was verified, and the actual total air demand of the Xinyuan coal mine was determined to be 15943.6m3/min. After verification, its ventilation capacity can meet the daily safety production needs of the mine.