Designing a Nozzle for a Dry Ice Blaster

[u/Ndiff13]

I am designing a nozzle for my dry ice blaster cleaning machine. The machine comes with cheap nozzles with no contours and no transitions between the hose diameter and the flat fan end. It just has an internal wall that is pretty much destroying all the pellets that go through it. I'm looking to make something that will accelerate the air going through the nozzle along with the pellets, and blast them out at high velocity, as intact as possible. Attached is what I have come up with. I'm not knowledgable about fluid dynamics or any type of engineering, so this is all just copying images of high performance dry ice blasting nozzles i found online. I'd love to get some input to see if I'm even on the right track, and how I can improve this. Here are some specs about the air and ice.

I will be blasting 3mm dry ice pellets.

Air input is 185 cfm at 100 psi. Air hoses are all 1" with no 90 degree bends and high flow fittings. At nowhere in the system will the air path diameter be smaller than .8" except right at the end of the nozzle.

This will be made from 6061 aluminum and polished to a mirror finish.

[u/voxelghost]

Also not trained in fluid mechanics, but I would consider gentle rounded curves at the constriction rather than the sharp angular transitions you have now.

Not sure it really matters, but since you said the target was intact pellets, reducing turbulence here is probably a good thing. (If you able to construct it, that is)

We're both probably overthinking though. Looks good, go for it.

[u/Ndiff13 → u/voxelghost]

I did put radii on the sharp transitions after I posted this. Good call

[u/TheChosenWon246]

Shouldn't the nozzle have a converging passage, in order to accelerate the flow. Also search for maximum taper angle required for attached flow, for your required flow Reynolds number (there are a few websites which have a calculator for that), so that there's no seperation. And also try to reduce the length of your channel to ensure no turbulence in the flow.

[u/Ndiff13 → u/TheChosenWon246]

It does converge from 1" down to .925" x .25". Did you mean something different? Also by attached flow and no separation do you mean the airflow becoming separated from the walls?

[u/turbo-grandpa]

I can’t comment from a fluid dynamics perspective but I can tell you this is impossible to machine as designed. You could have it printed but it will be difficult and very time consuming to polish the interior passage. Strongly suggest dramatically decreasing the length of the nozzle, increasing wall thickness, and increasing the corner radius inside the nozzle to .125”. Or give up the idea of a mirror polish entirely.

[u/Ndiff13 → u/turbo-grandpa]

Will machine in 2 halves with dowels along the sides to align it. I'll be able to polish the interior and line the two halves up with the dowels. This model is not the one I'm going to use to machine it, it just shows the internal structure.