Fluid Dynamics - Increasing Outlet Pressure

[HenIsMightier]

Hi everyone,

I am new to the forum, so please instruct me if I commit any posting faux pas in my first post.

Here is my dilemma: I have an oxygen concentrator that outputs .5-5 liters per minute of 95% concentrated oxygen at 5 - 7 PSI. This is just fine for medical use, but I am trying to adapt this machine to "spray oxygen" using an air brush (image attached) for aesthetic purposes. The air brush has a cup attached with a few drops of solution that would be nebulized and sprayed as a mist with the help of the oxygen. The air brush is attached to the machine with 7 feet of standard oxygen tubing.

I require the pressure to be high enough - I've heard 25 PSI, though I'm not sure - so that the oxygen can pick up the mist. Is there anything I can alter externally, such as the tubing size/length, the air brush, or the outlet on the machine, to increase the pressure without affecting the purity of the oxygen?

Any advice would be greatly appreciated. Please let me know as well if anything requires clarification or if further information would be helpful.

Thank you kindly,

George

 

[m.e.t.a.]

...I am trying to adapt this machine to "spray oxygen" using an air brush (image attached) for aesthetic purposes.

When you say "for aesthetic purposes" do you mean to say that you intend to re-purpose the oxygen concentrating machine for some non-medical use? (If so, could I ask out of curiosity what project you have in mind that requires an oxygen sprayer?)

If this is the case, then I have a feeling (though I am not sure) that you will not be able to convert an already narrow 5-7 psi stream of gas into a 25 psi jet of appreciable size without employing a more powerful pump. I suppose when you pinch the end of a hose pipe or cover it with your thumb, you do get a narrow but high-pressure stream of water...but I don't know if the same effect can be achieved with flowing gas as with flowing liquid. Somebody else will surely know.

If your plans for the oxygen concentrating machine are purely non-medical (i.e. nobody's life will be put in danger if you tinker with the machinery) then perhaps you could see if it is possible to simply supply the pump motor with more voltage? (Staying within the working specifications of the motor and pumping equipment, of course.) Not a very smart idea, I know, but I guess it would be the first thing I'd try.

 

[stewartcs]

I suppose when you pinch the end of a hose pipe or cover it with your thumb, you do get a narrow but high-pressure stream of water...

This actually decreases the pressure in that section and increases the velocity.
Hi George,

Welcome to the forum.

The maximum pressure of the device is just that...the maximum pressure it can develop. So the max you can hope to develop is 5-7 psi unless you add another device such as a booster pump to the outlet to increase it.

CS

 

[m.e.t.a.]

I suppose when you pinch the end of a hose pipe or cover it with your thumb, you do get a narrow but high-pressure stream of water...

This actually decreases the pressure in that section and increases the velocity.

Whoops. Thanks for the correction, stewartcs. (Sorry for the misinformation, HenIsMightier.)

So when you put your thumb over a hose pipe, that high-velocity jet that you create actually has lower pressure than the slow trickle of the original flow? The water molecules spread apart from each other just a little?

By symmetry, then, if you broaden the open end of the hose pipe, do you get a high-pressure, slow-flowing stream? The water molecules are somehow forced closer together? What a bizarre concept. Does this effect occur with flowing gas, too?

 

[stewartcs]

So when you put your thumb over a hose pipe, that high-velocity jet that you create actually has lower pressure than the slow trickle of the original flow?

Yes. Play around with the first link below and you'll see exactly how the pressure changes.

The water molecules spread apart from each other just a little?

Not really...see the second link below.

By symmetry, then, if you broaden the open end of the hose pipe, do you get a high-pressure, slow-flowing stream?

Yes, but only up to the total pressure developed by the pump.

Does this effect occur with flowing gas, too?

Yes, any fluid...however, please note that fluids in a gas phase behave slightly differently since they are a lot more compressible and liquids.

Check out these links:

http://www.ce.utexas.edu/prof/KINNAS/319LAB/Applets/Venturi/venturi.html

http://en.wikipedia.org/wiki/Venturi_effect

CS