Helium question - stratification

[2rmengineering]

Suppose I have a pressure vessel with internal volume of 10scf. Now assume the vessel is open to atmosphere of air at stp. I close the vessel, and then inject 90scf of helium gas. The chamber now has a 100scf mix of 90% helium, 10%air. The internal pressure is 10atm.

After a period of time, will the two gasses stratify into distinct layers such that if I had a valve I could remove the pure helium gas from the top of the vessel? See attached picture

 

[2rmengineering]

This is not a homework question. I am using helium gas for heat quenching some material and want to know how to economically recycle the helium gas as it is $.23/ft3.

 

[sreid]

Sorry, but the helium and air will not spontaneously separate.

 

[iainuts]

I'm afraid the helium won't separate out at all, it remains completely mixed. I've set up a few helium recovery systems and it sounds to me like the concentration of helium in your system is too low to be economically recovered. The 'dirtiest' helium recovery system I've worked on is one that wouldn't accept anything greater than about 800 ppm of air in the stream (remainder helium) and that was considered very high. We like to see it down in the 30 ppm range or below. So your 100,000 ppm system is way more dirty and even if you have a million SCF per year to recover, I don't think you'll get any takers.

 

[Compositepro]

Why would anyone use helium in a process that allows 10 air?

You could use the gas for party balloons.

 

[zdas04]

I see a lot of this kind of wishful thinking. People really WANT gas to act like liquid. The responses so far should show the futility of this kind of thinking.

David