| Coal and gas outburst is an extremely complex dynamic phenomenon that occurs in the production process of coal mines.It is manifested in the sudden ejection of a large amount of coal and gas from the coal seam to the mining space in a very short time,forming an outburst with strong impact and destruction.The coal-gas two-phase flow can easily cause heavy casualties and seriously threaten the safety production of coal mines.Carrying out research on the migration law of the two-phase flow of coal and gas outburst is of great significance for revealing the disaster-causing mechanism of coal and gas outburst,enriching and improving the outburst mechanism,and guiding on-site outburst prevention work.To this end,based on the self-developed coal and gas outburst roadway visual simulation test system,this paper carried out indoor coal and gas outburst physical simulation tests,and analyzed the temporal and spatial evolution of two-phase flow parameters such as shock wave overpressure,temperature and velocity,and outburst coal.The sorting and crushing characteristics of,the influence of different conditions on the migration characteristics of the two-phase flow and the disaster-causing effect are studied.This article draws the following main conclusions:(1)Based on similarity theory,independently developed a visual simulation test system for coal and gas outburst roadways,which is mainly composed of test cavity,stress loading system,gas source system,outburst system,simulated roadway,data acquisition and control system and auxiliary support facilities.The test system can carry out visual physical simulation tests of two-phase outburst flow under different gas pressures and different forming stresses.It has the advantages of integration of coal sample forming outburst,automatic outburst opening,outlining roadway visualization,and diversified data collection.(2)After the outburst occurs,pulverized coal and gas quickly migrate to the roadway,forming an outburst two-phase flow.The composition structure of the twophase flow changes dynamically between dense phase flow and dilute phase flow.Its migration patterns are represented by four types of flow patterns: suspended flow,stratified flow,dune flow,and tethered flow.The flow gradually evolved into a dune flow.At the same time,the two-phase flow compresses the air forward to produce shock waves,and the shock wave overpressure propagates forward in the form of alternating positive phase pressure and negative phase pressure.The shock wave front propagation speed is much greater than the speed of the pulverized coal flow,reaching supersonic speed;With the development,the temperature of the two-phase flow in the roadway gradually decreases,and the decrease rate decreases with the increase of the outburst distance;after the outburst is terminated,the small particle size coal powder is mostly moved to the dust bag farther from the outburst,showing Significant fragmentation and sorting phenomenon.(3)When the gas pressure is low,the migration pattern of the two-phase flow is mainly stratified flow and dune flow.With the increase of gas pressure,it gradually presents a tethered flow pattern;the shock wave waveform generated by the protrusion is lower in the gas pressure.It is closer to the typical gas pressure relief shock wave waveform,and changes greatly with the increase of gas pressure,which is specifically manifested as the existence of a long-lasting negative phase pressure;the peak overpressure of the shock wave and the shock wave propagation velocity follow The gas pressure increases with the increase of the gas pressure.The 3 tests(0.35 MPa,0.85 MPa,2.0 MPa)were 3.28 k Pa,10.29 k Pa,21.49 k Pa and 344.7 m/s,354.7 m/s,370.0m/s;outburst coal The flow rate and coal pulverization rate also increase with the increase of gas pressure.The 3 tests were 22.57 m/s,29.94 m/s,59.02 m/s and 8%,21%,28%.The results show that the higher the gas pressure,the greater the gas internal energy contained in the coal seam,and the stronger the impact and destruction ability of the two-phase flow generated after the outburst.(4)Comparatively analyze the influence of coal sample formation on outburst under the condition of 2.0 MPa gas pressure.The peak value of shock wave overpressure and the speed of shock wave are 15.3 k Pa and 361.6 m/s respectively,both are smaller than the loose coal sample,and the two-phase flow temperature drop in the roadway is 0.27 ℃～1.16 ℃ lower than that of the loose coal sample.At the same time,the relative outburst strength decreases after forming,but the ejected coal is broken more thoroughly,and the coal pulverization rate increases significantly,reaching 50%.The results showed that the molding pressure hindered the start of the protrusion to a certain extent.A large amount of gas internal energy is consumed during the crushing of formed coal,making the degree of crushing more significant,but the shock wave front energy generated was reduced.The research results have certain guiding significance for revealing the disaster-causing mechanism of coal and gas outbursts and formulating on-site outburst prevention measures.There are 45 pictures,16 tables and81 references in this paper. |
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