Air Cannon Air Speed Calculations

[BriggsFz]

I am working on an Air Blast Cannon for work and am having trouble finding the proper formulas to calibrate it. This Cannon needs to have a barrel with about a 4 inch bore. It will only be used to generate high speed air blasts, so it will not have a projectile. Are there any formulas or online calculators I can use to adjust the Air Reservoir pressures and volumes, relative to the the Barrel size, in order to zero in on my target air speed? I have found a few formulas that seem like they should work, but all of them require a projectile mass (which I don't have) and don't provide units, so I am unsure how to proceed. Additionally, these calculations don't have to be super precise, only accurate enough to give a rough idea on the materials I'll need to use. I am hoping you guys can provide formulas (with units preferably), useful website links, or even data from similar projects. I am looking forward to your responses. Thanks!

 

[jrmichler]

This sounds like a class project, yes? Everything you need is in your fluids book. Start with entrance losses. There will be good information under entrance losses, orifices, and flow nozzles. Then study turbulent flow in pipes, especially the part about how to deal with high velocity flows where the pressure drop is greater than about 10% of the absolute pressure. This is a complex problem, so there is no one single formula that tells you everything you need to know. You need to understand the principles, and work from them.

Or you could just buy an air cannon with all of the engineering done: https://www.martin-eng.com/content/product_subcategory/491/air-cannons-products.

Hint: If the goal is to design parts that handle the pressures, just assume that all pressures are either the highest tank pressure or atmospheric pressure. Then add a safety factor for shock loads.