| The pressure relief and permeability of coal seam is an effective method to improve the gas drainage rate and reduce the gas disaster.At present,the coal mine adopts the hydraulic measure to reduce the pressure and increase the permeability,But the water has negative influence on the migration and desorption of gas,and the working environment of the hydraulic measure is relatively bad,which brings the hidden danger to the mine personnel.Aiming at this problem,presents a new method to reduce the pressure and increase the permeability of coal by abrasive gas jet.For the existing abrasive gas jet use the subsonic nozzle,the maximum velocity of the nozzle exit is the sound velocity,which can not reach supersonic speed and is not conducive to the erosion of coal.It is can use the zoom nozzle to achieve supersonic speed.The nozzle structure is an important factor affecting the jet velocity,in order to improve the abrasive jet breaking coal erosion effect,it is very necessary to optimis the nozzle structure to improve erosion.Based on the scalable nozzle,this paper analyzes the nozzle outlet speed by using the continuity equation of aerodynamics and fluid,verifies the correctness of the theoretical formula,designs the nozzle with different Mach number,and use the numerical simulation verifies the relationship between the design nozzle structure and the theoretical formula.The discrete phase model was used to simulate the flow field structure of nozzle with different nozzle parameters.On this basis,the structural parameters of the nozzle are optimized,and the erosion effect of the nozzle is verified by experiments.The conclusions of this paper are as follows:(1)Research the key parameters of nozzle for the effect of gas flow acceleration and the change of gas in nozzle;determined the relationship between the nozzle exit velocity and the nozzle structure,Including the convergence angle,shrinkage ratio,expansion angle,throat length diameter ratio and throat diameter.Based on the theoretical analysis,desinged the four nozzle structures with different Mach number.The correlation between the design nozzle and the theoretical analysis is verified by theoretical analysis and numerical simulation.(2)The flow field structure of the far-field region under different pressure conditions is simulated numerically,and the development law of the flow field structure is analyzed.The erosion of the target is analyzed by the discrete-phase model The optimum nozzle type and coal breaking conditions are as follows:the nozzle with the distance of 100mm,the abrasive is 80 mesh garnet,the mass flow rate of the abrasive is10g/s and the erosion time is 15s,the inlet pressure is 25MPa,Erosion effect is best.(3)The single parameter method is used to optimize the structural parameters of the three mach nozzle with different convergence angle,shrinkage ratio,expansion angle and aspect ratio at the inlet pressure of 25MPa,and the nozzle structure parameters with the best erosion effect are obtained.The simulation results show that the inlet diameter is 4mm,the convergence angle is 53°,the nozzle shrinkage ratio is 2,the expansion angle is 10°,the throat aspect ratio is 3.This structure is the best broken coal nozzle structure.(4)The best structural parameters of four kinds of simulation results are selected to process the nozzle,and the erosion effect of the four kinds of nozzle structure is verified by the experiment system of the coal seam with abrasive gas jet.the experimental results show that the structure of the nozzle is optimized,the erosion depth is 47.29mm,the erosion volume is 14.89cm~3. |
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