Experimental Study On The Variation Rules Of The Flow And Nozzle Impact Stress Of Supercritical CO₂ Gas Explosion

An effective way to achieve high,safe and efficient mining of high gas coal resources is to extract gas efficiently.For the limitation of the traditional anti-reflection technology of the high gas low permeability coal seams,a new type of low-permeability high-gas coal seam supercritical CO₂ gas explosion anti-reflection technology comes into being.However,at present,there is still a lack of comprehensive understanding of the rules of the explosive gas flow during the supercritical CO₂ gas explosion and the change of the impact stress during the gas explosion hole jet process.In this paper,the combination of theoretical analysis and experimental research was used to study the rules of gas flow and impact stress of supercritical CO₂ gas explosion.The main research work and achievements are as follows:Using the self-developed gas explosion generating device,the gas explosion tube and the nozzles with different nozzle holes were designed for gas explosion test.The high-speed acquisition card was used to improve the test precision,and we have studied the change rules of the temperature,pressure,density and other physical parameters during supercritical CO₂ gas explosion under the initial temperature and pressure.The results show that the whole flow of explosion gas in supercritical CO₂ gas explosion tube can be divided into three regions:supercritical zone,second-order phase transition zone and first-order phase transition zone.The pressure and temperature of CO₂ decrease at first and then stabilize with the increase of flow distance,and increase with the increase of initial temperature and initial pressure.The change rules of the density and viscosity of CO₂ are similar to each other in the process of explosion gas flow,which increase with the increase of flow distance and fluctuate stably at first and then decrease greatly.The stable fluctuation distance increases with the increase of initial temperature and pressure.The flow velocity of explosion gas shows the pulse fluctuation with the increase of flow distance.The effect of initial temperature variation on the flow velocity fluctuation is greater than that of initial pressure.The results of the experimental study on impact stress of gas explosion nozzle jet with different number of holes show that:the change of impact stress of double nozzle jet experienced three stages:stress surge,stress reduction and stress deceleration attenuation.The time history curve of impact stress is characterized by pulse curve,and the impact stress decay time is longer than that of surge time.The change of impact stress of four-nozzle goes through four stages:stress increase,stress surge,stress reduction and stress deceleration,and the length of increasing period of impact stress is approximately equal to that of the decreasing.The impact stress increases with the increase of initial temperature and pressure,and the change of impact stress caused by the change of initial pressure is more obvious than that of initial temperature.In the jet process of symmetric double-hole nozzle,the pressure of the nozzle wall is similar to the rules of impact stress,and the ratio of the nozzle area to the cross-sectional area of the nozzle is closer to1,the impact stress is larger.The relationship between the impact stress peak valueP_max and the initial temperatureT’and initial pressureP’of different nozzle has been derived by using the MATLAB experimental data,the formula isP_max（28）aT’（10）bP’（10）C.The initial temperature change has greater influence on the peak value of the four-hole nozzle impact stress than the double-hole nozzle,while the initial pressure change has less influence on the peak value of the four-hole nozzle impact stress than the double-hole nozzle.The paper has 84 diagrams,5 tables and 74 references.