Aerosol Flow Through a Converging-Diverging Micro-Nozzle

Abstract

Cold spray is a material deposition process used to deposit metallic features for use in applications such as corrosion prevention, dimensional correction and repair, and wear resistant coatings. Micro Cold Spray Direct Write (MCS-DW) is a variant of the cold spray process in which metal particles are accelerated and focused to print fine features on flexible and rigid substrates with no postprocessing required. This paper presents results of numerical studies on the flow of 2 µm and 6 µm diameter silver particles through a converging-diverging micro nozzle with helium gas. The flow of helium was simulated by solving Navier Stokes equation using commercial software. The trajectory and velocity of the aerosol particles were determined using a Lagrangian particle tracking algorithm with a combination of Stokes drag force and Saffman lift force acting on the particles. A comparison of the effect of different corrections applied to Stokes and Saffman forces as well as the effect of Magnus force on the trajectory and velocity of aerosol particles is studied. The effect of particle rotation creating Magnus force is found negligibly small compared to Saffman force for particles of 2 µm diameter, however, the effect is found to be significant for particles of 6 µm diameter. A proposed converging-diverging nozzle is shown capable of accelerating silver particles to velocities as high as 600 m/s and enables aerosol beam widths as thin as 50 µm.