Air flow/pressure drop through a slit type nozzle

[handleman]

It's been far too long since fluids for this guy... I'm looking to roughly design a sorta long, thin nozzle/outlet, something like an air knife but with a much lower supply pressure (maybe 5~10 psi), and a really low flow rate to go with it. I figured "air flow through a narrow slit" would be pretty easy to find a plug-and-chug for, but I've not found anything yet. Am I just looking for the wrong thing, or is it so dead simple that nobody bothers to write it up, or so complicated that nobody bothers to write it up? I'm not necessarily looking for a 3 decimal precision result, more like an order-of-magnitude starting point for an adjustable type design before I go digging through the attic for my old textbook...

 

[btrueblood]

Use the orifice flow equations, but substitute your slot area for the pi-r^2 term, and adjust the Cd or K flow coefficient downwards by 10% or so for a first guess.

 

[btrueblood]

or to go further, take a look a NASA/NACA archives, a quick search on google found this one -

http://naca.central.cranfield.ac.uk/reports/arc/cp/0013.pdf

 

[Compositepro]

Such a nozzle is strongly affected by how flow approaches the slit. Otherwise, do as btb suggests. You might also find that the Coanda effect is relevant.

 

[dgallup]

At those pressures you are sub-sonic so it's just incompressible flow. Sounds like you only need a ball park figure at this point since you have 100% pressure range.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.