Analysis and modelling of particle velocities in micro-abrasive air jet

Abrasive jet micromachining (AJM) is a non-traditional technology that can effectively remove hard and brittle materials at high cut quality. A key requisite in modelling the AJM process is to determine the velocities of abrasive particles. In this paper, a theoretical analysis for particle velocities within a micro-abrasive air jet is presented and the associated particle velocity models are developed. The particle velocities at the nozzle exit are determined based on the nozzle length, particle mean diameter, particle density, air density and air flow velocity. The distribution of particle velocities along the jet centerline downstream from the nozzle and the particle velocity profile at a jet cross-section are also modelled considering surrounding air entrainment and air-particle interaction. A numerical solution to the models is developed to determine the particle velocities by dividing the nozzle and the jet flow in air into small segments along the jet axial direction. The developed models are finally verified by comparing the calculated particle velocities with those from a particle image velocimetry (PIV) measurement of the velocity distribution in micro-abrasive air jets. It is shown that the model calculations and the corresponding experimental results are in good agreement with less than 4% average errors.