Nitrox gas separation

[Teamcasa]

Trying to change peoples long held paradigms is virtually impossible. Even after the history, science, physics and logic is explained many will never change their mind and rely solely on the anecdotal evidence.

Here are some examples:
If Nitrox sits in a tank for an extended period the nitrogen will separate from the oxygen.
Driving with your tailgate down will give you better mileage.
Shaving makes your beard grow in thicker.
Thomas Edison invented the electric light bulb.
Men have one less rib than women.
The US never attacked without being attacked first until Iraq.
Having less than 300lbs in your tank will require a VIP because water can get in.
The Earth is flat.
They could make an electric car today, but the oil companies won’t release the secret patents to a new battery.

I don’t want to debate the above, but no doubt someone will disagree, even after they do a Google search for the truth.

 

[Randy43068]

Dave, that's actually quite humorous, but true.

 

[cool_hardware52]

In my experience the value of "mixing" is obtaining a stable analysis without delay after blending.

Consider a bottle that has been filled with O2, He, and HP air and analyzed. Let's say it's a bit short of the target percentage of He and you are equipped to boost in a little more.

This last bit of gas will be introduced slowly and may not immediately mix fully. What does that do to your analysis?


Tobin

 

[Randy43068]

Tobin, gas doesn't work that way. Once it's introduced into the container it's mixed, and rather quickly.
Gas does not behave as a liquid does.

It's been a lot of years since Chem and I've forgotten a lot from the classes I really didn't like.

 

[Walter]

Trying to change peoples long held paradigms is virtually impossible. Even after the history, science, physics and logic is explained many will never change their mind and rely solely on the anecdotal evidence.

Here are some examples:
If Nitrox sits in a tank for an extended period the nitrogen will separate from the oxygen.
Driving with your tailgate down will give you better mileage.
Shaving makes your beard grow in thicker.
Thomas Edison invented the electric light bulb.
Men have one less rib than women.
The US never attacked without being attacked first until Iraq.
Having less than 300lbs in your tank will require a VIP because water can get in.
The Earth is flat.
They could make an electric car today, but the oil companies won’t release the secret patents to a new battery.

I don’t want to debate the above, but no doubt someone will disagree, even after they do a Google search for the truth.

You'll probably get more argument about Edison than the rest, but it's also false.

 

[cool_hardware52]

Tobin, gas doesn't work that way. Once it's introduced into the container it's mixed, and rather quickly.
Gas does not behave as a liquid does.

I have no doubt that gases mix and stay mixed, but gas at 200 bar also does not behave the same as gas at a few bar.

Please explain why the analysis changes over time.

If you analyze immediately after introducing a small amount of say He without mixing the sample will have a higher percentage of He and lower percentage of O2 than what is present in the tank.

If you either wait, or agitate the He percentage will fall and the O2 percentage will rise.

I can demonstrate this phenomena even after a quick blast of gas out of the tank to clear the valve and dip tube.

Tobin

 

[Gombessa]

What's interesting to me is that of all the scuba "myths" we've heard over the years, this one sounds ridiculously easy for nearly anyone to test. You'd think we'd have a definitive answer by now.

 

[Randy43068]

I have no doubt that gases mix and stay mixed, but gas at 200 bar also does not behave the same as gas at a few bar.

Please explain why the analysis changes over time.

If you analyze immediately after introducing a small amount of say He without mixing the sample will have a higher percentage of He and lower percentage of O2 than what is present in the tank.

If you either wait, or agitate the He percentage will fall and the O2 percentage will rise.

I can demonstrate this phenomena even after a quick blast of gas out of the tank to clear the valve and dip tube.

Tobin

I can't. When I worked in a dive shop we had this discussion over and over. I actually saw the reading change after rolling a tank and I can't explain it other than to say what we saw may have something to do with temperature. Rolling the tank on the cement floor "could" sink some of the heat from the cylinder.

I've seen this happen but I just cannot wrap my mind around the issue of the gasses not diffusing in the amount of time between mixing. Several minutes, in fact.

So, honestly don't have an answer, only speculate that somehow the difference is temperature related to the measurement instruments.

 

[Randy43068]

What's interesting to me is that of all the scuba "myths" we've heard over the years, this one sounds ridiculously easy for nearly anyone to test. You'd think we'd have a definitive answer by now.

Funny you say this. I set out to fugure out why, but got busy and didn't put any time or effort into it.

 

[georoc01]

What I was thinking was..if nitrox is enriched air, and it could seperate into its components, then what is to keep just regular air fills from seperating?

And I have friends who are absolutely convinced that the automakers are in bed with the oil companies who would shut off their access to plastic & rubber components if they made a purely electric car.