Research On Nozzle Of Wear Micro Abrasive Water Jet

In the water jet system, the nozzle is a key component to determine the performance of the jet. In this thesis, a simulation of multiphase flow in the nozzle based on computational fluid dynamics is presented. Numerical simulation was conducted using the Fluent in order to explore the impact of nozzle wear.Firstly, a mathematical model of particles in two-phase flow was simplified. And then the multi-phase flow model is established to simulation the proceeds of the flow field in nozzle based on Eulerian Equation. The study found that because of the effect of gravity and negative pressure, the abrasive get into the nozzle. Upon entering the mixing chamber, abrasive speed is fluctuating. The abrasive velocity begins to stabilize until getting to the convergence segment. After entering the mixing chamber, the abrasives will be exponentially approaching the speed of the fluid if neglecting the relative velocity slip and energy loss.The simulation result show that there are three high pressure area inside the nozzle which expressed a. b. c zone. a zone is located at the wall where near the abrasive inlet. b zone is located at the wall near the junction of the convergence section and the mixing chamber wall, czone is located at the wall near the junction of focusing tube and convergence segment. with increasing of the convergence angle, the range of b zone and C zone will be expanded, the peak will be also increased. When the convergence angle is less30°the changes of b zone and c zone are not obvious. it is considered to be appropriate value of about30°for convergence angle.The simulation results also show that the length and diameter of the focus tube have effect on the pressure of abrasive inside the focusing tube. By evaluation criteria of exit velocity of abrasive nozzle,,through horizontal comparison, the ratio of length and diameter of the focusing tube is appropriate between25to37.5.By analysis of the particle trajectory in the nozzle by DPM, it is found that some particles do not directly get into the focusing tube. But circulate at the spout. It leads strong nozzle erosion by the abrasive in the juncture of focusing tube and convergence.in the focusing tube, the nozzle erosion increase with the extension of the axial length, and then get to the peak in somewhere, finally fluctuate sightly.