Dense Particulate Flow in a Cold Gas Dynamic Spray System

The effect of particle-gas and particle-particle interactions in a cold spray process is studied when the particle loading is high. To examine the effect of the presence of a dense particulate flow on the supersonic gas, an Eulerian-Eulerian approach is used. It is found that when the volume fraction of the injected particles is increased, the turbulence of the gas phase will be augmented by the motion of particles and consequently, the shape, strength and location of the compression and expansion waves will be altered. Shock-particle interactions are demonstrated for various volume fractions. Another important parameter which will affect the spraying deposition efficiency is the substrate stand-off distance. It is found that the stagnation pressure alternates for different stand-off distances because of the formation of compression and expansion waves outside the nozzle exit. Particle normal velocity upon impact is a strong function of the stagnation pressure on the substrate as particles must pierce through the bow shock formed on that region. The substrate stand-off distance can be optimized to provide minimal pressure build-up on the substrate. This will result in a higher normal velocity upon impact and thus a higher deposition efficiency.