Research on hydraulic cavitation bit of coal seam based on throttling pressure drop principle

Hydraulic cavitation in coal seam can increase the permeability of coal seam and improve the efficiency of gas extraction. However, the analysis and calculation method of throttling control mechanism of hydraulic cavitation bit is still not perfect. In this paper, firstly, the composition of hydraulic cavitation device, the detailed process of hydraulic cavitation, the structure and principle of hydraulic cavitation bit and the mechanism of throttling tube are introduced. Then, the flow inside the throttling tube is simplified into one-dimensional fluid for analysis. According to the continuity equation, momentum equation and Bernoulli equation, the mathematical expression of the pressure distribution inside the throttling tube is deduced, and the pressure distribution curve inside the throttling tube is drawn. Secondly, the simulation model of the throttling tube is established according to the turbulence model, and the pressure distribution and velocity distribution inside the throttling tube are analyzed. Finally, the opening and closing experiment of the hydraulic cavitation bit is carried out, and the relationship between the opening and closing flow and pressure of the hydraulic cavitation bit, the reduction diameter of different throttling tubes and the pressure drop value is studied. This study provides the drilling tool support for gas extraction and permeability enhancement in low-permeability coal seam, and provides the theoretical support for the design of throttling pipe of hydraulic cavitation drill.