Negative pressure distribution of variable mass flow in coal mine drainage boreholes

A high-pressure and large-diameter extraction borehole is used in coal mines due to lack of understanding of the mechanism of negative pressure in the process of gas extraction, which will lead to problems such as poor gas extraction and collapse of the borehole. In order to solve these problems, the flow and pressure distribution in the process of variable mass flow of gas drainage borehole were studied based on factors such as orifice pressure, bore diameter, and bore flow. Firstly, we built a testing platform for variable mass flow pressure distribution and established a variable mass flow energy model and pressure distribution model. Secondly, the correlation between pressure distribution and orifice pressure, borehole diameter, and borehole flow in the process of variable mass flow was calculated by combining laboratory testing with numerical calculations. Finally, the results showed that with the increase in borehole length, pressure, and flow exhibited a downward trend during the variable mass flow of the borehole. Additionally, the pressure distribution in the borehole had a negative exponential relationship with borehole pressure and the diameter of the borehole. The pressure distribution in the borehole had a power-exponential relationship with the gas flow. These research results will provide a reference for the selection of reasonable parameters.