Research On Pre-breakdown And Shock Wave Characteristics Of High Voltage Pulse Discharge In Water

Gas is a mixed gas with CH₄as the main component produced in coal seams.It is not only an explosive and dangerous gas,but also a recyclable resource.Coal seam gas permeability enhancement technology can improve the efficiency of gas drainage and coalbed methane extraction,and has important value for coal mining and gas recovery after gas drainage.Fracturing coal seams with shock waves generated by high-voltage pulse discharges in water is a new type of coal seam anti-reflection technology,but it is not yet mature and has no engineering application precedent in domestic coal mines.Taking this as the research background,this paper studies the pre-breakdown of high-voltage pulse discharge in water and the transmission process of shock wave,in order to provide theoretical support for the practical application of coal seam anti-reflection.The main research work and conclusions of the thesis are as follows:Firstly,the water between the needle and the plate electrode is selected as the research object.A fluid mathematical model of water breakdown and discharge under the action of pulse voltage is derived and established.The COMSOL software is used to simulate the development of streamer morphology,the change of electric field intensity and the migration law of charged particles during the pre-breakdown of water under the action of nanosecond pulse voltage.The results show that under the action of the pulse voltage,the water at the tip of the needle ionizes first,and the generated space charge strengthens the electric field of the discharge head.The streamer head continues to develop towards the plate electrode and eventually forms a plasma channel.In the development process of streamer,the concentration of positive ions at the same position at the same time is always greater than the concentration of electrons,and the maximum value of electric field intensity always appears at the same position as the maximum value of space charge density.Secondly,the influence of the distance between the electrodes,the amplitude of the pulse voltage and the voltage rise time on the water breakdown process are studied separately.The analysis of the results shows that with the increase of the distance between the electrodes,the breakdown time of the water and the average development speed of the streamer increase;When the pulse voltage amplitude increases,the development speed of the streamer increases;With the decrease of the rising edge time t₀,when the streamer develops to the same position,its channel radius increases,while the peak value of the electric field intensity decreases.Finally,based on the basic theory of the explosion expansion of the cylinder,taking the relevant data at the boundary of the plasma channel obtained by simulation results as the initial parameters,the simulation geometric model of the high-temperature and high-pressure plasma explosion in water is established by using the ABAQUS software with the plasma channel and water regarded as Euler bodies.Furthermore,the change law of shock wave in water with time and space is obtained,and the power function attenuation relationship between the pressure amplitude and velocity amplitude of the shock wave and the transmission distance is given.And based on the engineering background,the effect of water depth on the shock wave transmission characteristics is studied,and the results show that the increase of hydrostatic pressure has an inhibitory effect on the shock wave transmission.This paper uses numerical simulation to study the pre-breakdown of water and the transfer process of shock waves.On the one hand,it explores the movement of charged particles from a micro level.On the other hand,the conclusions obtained are of macroscopic reference value for determining the relevant technical parameters of the high-voltage pulse discharge device in water.There are 47 figures,11 tables and 82 references in this paper.