Research On Breakdown Process And Pressure Wave Characteristics Of High Voltage Pulse Discharge In Water

In recent years,the application research of high voltage pulse discharge technology has been paid more and more attention,and has been successfully applied in medical in vitro lithotripsy,oil recovery and other aspects.Research progress has been made in the fields of sewage treatment and soil remediation.The realization of gas permeability improvement in coal seam through impulse pressure wave generated by high voltage discharge in water has also become a hot topic of mining,safety and electrical cross-disciplines,but there are still many problems to be studied,and there is no engineering application precedent.In this thesis,the theory and simulation of discharge process in water are studied,and the actual discharge test is carried out,and the characteristics of the pressure wave generated by discharge are discussed.The main research contents and conclusions of this thesis are as follows:Firstly,based on the field ionization theory,the fluid mathematical model of water discharge under the action of pulse voltage was derived.The streamer motion rule,the change of electric field intensity and the distribution of charged particles during the pre-breakdown process were simulated by COMSOL software.The results show that the water medium at the tip of the needle electrode first ionizes,and the generated space charge strengthens the electric field of the streamer head,and the streamer head moves towards the plate electrode until the plasma channel is formed.The electron migration rate is up to 10⁶m/s,while the hydrogen ion is only hundreds of m/s.The concentration of hydrogen ion and electron at the same position at the same time is much larger than that of hydroxide ion,and the maximum electric field intensity always appears in the same place as the maximum net charge density.The streamer morphology is generally cylindrical,which provides a theoretical basis for the subsequent construction of cylindrical equivalent arc detonation model.Secondly,according to the correlation between the energy balance equation and the physical quantities in the passage,three empirical formulas(σ₁,σ₂,σ₃ of conductivity with different temperature sensitivity degrees were used to establish the detonation model of the arc passage,so as to describe the changing characteristics of the physical quantities of the passage current,radius,deposition power,deposition energy,pressure,distance impact pressure,etc.The simulation results of the pre-breakdown process are used as the input parameters of the model The results show that the discharge current and the deposition power both oscillate periodically,and the oscillation frequency of the deposition power is twice that of the discharge current.Channel radius and deposition energy tend to a certain value respectively,and the relationship between them isr_σ2>r_σ1>r_σ3 andE_σ2>E_σ1>E_σ3.The pressure inside the channel can reach hundreds of Mpa,and its peak pressure size isP_Mσ1>P_Mσ2>P_Mσ₃.The"volume equivalence principle"is adopted to calculate the propagation characteristics of impulse pressure wave.When the distance from the discharge center is 0.5m,the peak pressure in the modelσ₂ is only 0.1139%.Finally,the high voltage pulse discharge test platform in water is designed and built independently,including the design of discharge reaction vessel,discharge electrode design,pressure sensor system design,etc.The charging voltage of the pulse power supply was set as 20k V,25k V,30k V,35k V and 40k V respectively,and the waveform data of impulse current and pressure wave intensity corresponding to 3.5cm,4.5cm,5.5cm and 6.5cm from the discharge center under the action of the above voltages were recorded respectively.Analysis of test data shows that with the increase of the propagation distance,the amplitude of the pressure wave decreases in the form of a power function,and its power index is in the range of-0.94 to-1.12.With the increase of the charging voltage of the pulse power supply,the amplitude of the pressure wave increases in the form of a power function,and its power index is within the range of 0.63-0.75.In addition,the experimental results in this thesis are compared with the classical discharge waveform data,and the causes of the experimental errors are analyzed.The correctness of the arc detonation model presented in this thesis is verified by the experimental data of other scholars.The theoretical,simulation and experimental research on the pre-breakdown process,main discharge process and pressure wave propagation characteristics of high voltage pulse discharge in water is carried out in this thesis,which lays a certain foundation for the realization of gas reflection improvement in coal seam in the future.There are 54 figures,8 table and 109 references in this thesis.