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

Premixed abrasive water jet is an effective technology to break through the technical bottleneck of effi- cient 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 acceler- ated 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 ob- tained:at a fixed pressure, the liquid-solid energy conversion efficiency of abrasive jets with different mass concentra- tions 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 ab- rasive 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 short- ened, resulting in the jet energy not being converted into the kinetic energy of the abrasive in time. Compared with in- creasing 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.