Mine gas extraction in China is difficult due to the characteristics such as micro-porosity,low-permeability and high adsorption of coal seams.The pulsed mechanismof a high-pressure pulsed water jet was studied through theoretical analysis,experimentand field measurement.The results show that high-pressure pulsed water jet has threedynamic properties.What's more,the three dynamic effects can be found in low-permeabilitycoal seams.A new pulsed water jet with 200-1 000 Hz oscillation frequency andpeak pressure 2.5 times than average pressure was introduced.During bubble collapsing,sound vibration and instantaneous high pressures over 100 MPa enhanced the cuttingability of the high-pressure jet.Through high-pressure pulsed water jet drilling and slotting,the exposure area of coal bodies was greatly enlarged and pressure of the coal seamsrapidly decreased.Therefore,the permeability of coal seams was improved and gas absorptionrate also decreased.Application results show that gas adsorption rate decreasedby 30%-40%and the penetrability coefficient increased 100 times.This proves that high-pressurepulsed water is more efficient than other conventional methods.
LI Xiao-hong ZHOU Dong-ping LU Yi-yu KANG Yong ZHAO Yu WANG Xiao-chuan
Because of the complication of turbulence's mechanism and law as well as thejet pressure in nozzle is difficult to test by experiment, five turbulent models were appliedto numerically simulate the turbulent flow field in convergent-divergent nozzle. Theoryanalysis and experiment results of mass flow rates conclude that the RNG к-з model is themost suitable model. The pressure distribution in the convergent-divergent nozzle was revealed by computational fluid dynamic (CFD) simulating on the turbulent flow field underdifferent pressure conditions. The growing conditions of cavitation bubbles were shown;meanwhile, the phenomena in the experiment could be explained. The differential pressure between the upstream and downstream in nozzle throat section can improve thecavitating effect of cavitation water jet.
LU Yi-yu LIU Yongc LI Xiao-hong KANG Yong ZHAO Jian-xin
