I'm planning to build a DIY pitot tube to measure the outlet flow velocity of the cold spray gun nozzle. I'm thinking to use a syringe needle (for total pressure) and two pressure sensors. I'm worried about the accuracy of the device. I am OK with +-30 m/s.
Outlet nozzle cold-spray speeds vary from 0 to 600 m/s.
Could you recommend me something for me?
Dear Aleksandr,
I can't tell you how to measure the air velocity at the nozzle exit with an accuracy of 30 m/s, but I can say with confidence that for the cold spraying process, such measurement accuracy is meaningless, just like measuring the gas velocity in general. The fact is that during spraying, only the velocity of the particles at the moment of their impact on the substrate is important, and this velocity has very little to do with the velocity of the gas. In addition to the gas velocity, the particle velocity is affected by the length of the nozzle, the distance from the nozzle to the substrate, and most importantly, the particle size. All this makes it impossible to directly "tie" the particle velocity to the gas velocity and makes the measurement of the latter meaningless. To measure the actual speed of particles, there are special optical instruments, for example, the "Accuraspray", which, although they have a very large measurement error, allow one to determine the order of magnitude of the average particle speed at the point of contact with the substrate.
Vadim Verlotski Thank you for your response! I know that knowing only flow velocity is meaningless, but I can check it with my CFD simulation and then add particles in it to define approximately their speeds.
By the way, in our lab we have Accuraspray, but I am not sure that it's suitable for cold spray.
You cannot apply the Accuraspray directly to cold spraying as the particles do not glow, but if you use a powerful light source (possibly laser light), you can try to determine the particle velocities from the reflected light. Of course, the temperature of the particles in this case will be shown incorrectly.
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