One Dimensional Flow Law And Pressure Distribution Of High Pressure Gas In Blast Hole

High-pressure gas impact fracturing and anti-reflection technology have many advantages such as strong applicability,safety and controllability.The flow characteristics and pressure distribution law of high-pressure gas in the blast hole are of great significance to the study of the coal fracturing effect and mechanism.This paper explores the pressure distribution law in the blast hole through the experiment method from a high-pressure gas impact test system which is designed and developed by the author.Comprehensive analysis from the previous research on the mechanical parameters of the coal test,the coal is categorized into five class in terms of uniaxial compressive strength,elastic modulus,and longitudinal wave velocity,which are extra-hard coal,stiff coal,hard coal,medium-hard coal and soft coal.The selection and proportion of these five coals,which with different strength,using for simulation are determined through a similar simulation test.The high-pressure gas impact test system includes two parts: a high-pressure gas fracturing device and a data acquisition device.The system has different confining and impact pressures(0-80MPa)which can be used to complete coal impact fracturing test.The high-pressure gas fracturing device has three major parts,the pressurization system composed of an air compressor and gas booster pump;the control system composed of autoclave,high-speed solenoid valve and digital pressure gauge;the connection system composed of high-pressure pipeline;The data acquisition device includes PVDF piezoelectric film sensor,dynamic strain gauge,data acquisition instrument and acquisition analysis system.According to the parameter and ratio of the simulated coals,the test block with500mm×500mm×500mm is fabricated for the simulation of high-pressure gas impact test.The test results of the gas flow characteristics and pressure distribution law inside the blast hole show that the physical parameters such as pressure,velocity,density are a function of space variable with time,and the gas flow is similar to one-dimensional unsteady flow;the gas pressure-time history curve of the hole wall show the typical triangular pulse characteristics of approximately linear rapid rise before the peak and nonlinear decrease after the peak,and the time in pressure decay stage is longer than the pressure rapid rise stage;the pressure on the inner wall of the blast hole rises quickly with the impact pressure increases,therefore the slope of the pressure-time history curve in the first half of the curve increases with the increase of the impact pressure;the peak pressure decreases with the increase of the distance from the jet core impact area when the impact pressure decreases,the smaller the peak pressure of the hole wall and the weaker the impact of gas;When the impact pressure is the same,the blast hole bottom has the highest peak pressure,while the peak pressure at the surface is the smallest,and the pressure distribution on the whole wall is uneven.Since the energy released by the gas into the blast hole is the only energy source for fracturing and enhancing the permeability of the coal,understanding the pressure distribution of the pore wall has important scientific significance and practical value for the use of high-pressure gas impact fracturing coal technology to improve the gas drainage rate.Provides a theoretical and experimental basis for the in-depth research on the mechanism of coal fracturing.