磨料质量分数对预混合磨料水射流破岩效果的影响

Influence of abrasive mass fraction on the effect of premixed abrasive water jets on rock breaking

预混合磨料水射流是突破煤矿深长钻孔内高效破煤岩技术瓶颈的有效技术,在坚硬顶板治理、沿空留巷和硬煤增透具有广泛应用前景。磨料质量分数是影响其破煤岩效果的重要因素。为明确磨料质量分数对磨料加速、分布以及冲击动能的影响,基于离散元的耦合模型(CFD-DEM模型),考虑颗粒间的摩擦、碰撞,添加颗粒相体积分数和动量源相,修正VOF多相流模型,开发用户自定义函数(UDF)通信接口,精确计算了磨料质量分数对磨料颗粒加速运动与分布的影响,准确描述了磨料粒子对水射流流场的影响。结合预混合磨料水射流破岩实验,得到了以下结论:在固定压力下,不同磨料质量分数的射流液固能量转化效率不同,导致磨料冲击动能不同。提高磨料质量分数,能够提高破煤岩效果,但存在最优值。每一压力条件下都有与之相适配的最优质量分数,此质量分数下能量转化效率最高,磨料冲击动能最大。如射流压力5 MPa时,80目(0.178 mm)石榴石最优质量分数为11%。同一质量分数下,提高射流压力可提高磨料冲击动能,但是能量转化率和利用率降低。提高压力使射流速度增加,曳力增大,但射流与磨料接触时间缩短,导致射流能量未能及时转化为磨料动能。相较于提高射流压力,适当增加磨料质量分数以提高能量转化效率和能量利用率,是达到最佳破煤岩效果的更经济低能耗的方式。

Premixed abrasive water jet is an effective technology to break through the technical bottleneck of efficient coal rock breaking in deep and long holes in coal mines.It has broad application prospects in hard roof control,gob-side entry retaining and hard coal antireflection.The abrasive mass concentration is an important factor affecting its coal rock breaking effect.In order to clarify the effect of abrasive mass concentration on abrasive acceleration,distribution and impact kinetic energy,based on the coupled model of discrete elements(CFD-DEM model),considering the friction and collision between particles,this study has added particle phase volume fraction and momentum source phase,modified the VOF multiphase flow model,developed user-defined function(UDF)communication interface,accurately calculated the effect of abrasive mass concentration on the accelerated motion and distribution of abrasive particles,and exactly described the effect of abrasive particles on the water jet flow field.Combined with premixed abrasive water jet rock breaking experiments,the following conclusions are obtained:at a fixed pressure,the liquid-solid energy conversion efficiency of abrasive jets with different mass concentrations is different,resulting in different abrasive impact kinetic energy.Increasing the abrasive mass concentration can improve the coal rock breaking effect,but there is an optimal value.For each pressure condition,there is an optimum mass concentration with which the energy conversion efficiency is highest and the kinetic energy of abrasive impact is greatest.For example,the optimum quality concentration of 80 mesh(0.178 mm)garnet is 11%at a jet pressure of 5 MPa.At the same mass concentration,increasing the jet pressure can increase the kinetic energy of abrasive impact,but the energy conversion rate and utilization rate are reduced.The pressure increase enables the jet velocity to increase and the tracing force to increase,but the contact time between the jet and the abrasive is shortened,resulting in the jet energy not being converted into the kinetic energy of the abrasive in time.Compared with increasing the jet pressure,increasing the abrasive mass concentration to improve the energy conversion efficiency and energy utilization is a more economical and low energy consumption way to achieve the best coal rock breaking effect.