EANx Shaken or Stirred?

[lamont]

whenever i get p-p fills at shops the number that i get right after they've been filled always agrees within a few 0.1% of what i analyze at the dive site.

maybe you've got O2 sensors that are unusually sensitive to the temperature of the gas?

now you're all going to make me look up the physics of diffusion that i've forgotten since undergrad....

 

[MXGratefulDiver]

Bob, how about you let those of us without analyzers know how this WOULD go?

Typically 0.1 or 0.2 percent ... which falls within the "margin of error" level of the sensor ...

... Bob (Grateful Diver)

 

[lamont]

bizzare...

my first rough shot at surfing around the net trying to figure this out gives an RMS velocity of around 500 m/s for N2 and O2 and 1348 m/s for He, but a mean-free path at 300 bar of around 50 A for He. that gives a diffusion coefficient of around 2.5 x 10**-6 m^2/s which means an average delta-T of like 400000 seconds (111 hours) to travel a meter.

 

[Rick Murchison]

It could be the rates I use (very slow - practically no warming of the tanks at all) that allows some stratification of gasses, but I find my O2 reading is a couple to several points off (depending on the mix) if measured right after finishing a fill, but right on after a couple hours. So I've gotten in the habit of not even taking a reading for awhile after the fills.
Rick

 

[CBulla]

Sooooooo.. its not like a Black and Tan? Black being Oxygen as it is heavier according to the periodic table, Tan being Nitrogen as it is lighter? Given time the black will mix with the tan but on a slow mix it will take a while as the specific gravity of Bass is also slightly lower than Guinness (4% for Bass vs. 4.2% for Guiness). Of course this is the prescribed mix from Guinness promotional advertising and was posted as the correct mixture on the 1759 Society charter members website a few years ago.

Will the Black (actually its dark red but thats a moot point) actually mix with the tan? Yes, when left to sit and settle the black will mingle in with the tan and sooner or later you get an interesting reddish and very flat beer. Will O mix with N if you let it sit a while.. yup.. it just takes a while.. well, it doesn't if you dont use the spoon and just let the tan blast into the black then you get it pretty close to what it will be if you trickle into the glass slow.

Whatever you do, don't roll the Black & Tan around the bar in the glass.. its very messy and a waste of perfectly good BEvERage.

 

[Rick Murchison]

Sooooooo.. its not like a Black and Tan?

I think it's more along the lines of "what goes in last comes out first" until it's had a chance to mix.
Rick

 

[JRScuba]

Just finished a Nitrox course. The instructor said that the tanks should set for awhile after a fill to ensure a correct reading. Said that
if you are in a hurry, roll the tanks on the floor. There is always a shortcut to getting something done. If it works do it.
Looking for an answer to the question might not be worth the time to investigate it.

Eric, I think I know the shop your talking about. Yes, they are
very reputable.

Joe

 

[DA Aquamaster]

It could be the rates I use (very slow - practically no warming of the tanks at all) that allows some stratification of gasses, but I find my O2 reading is a couple to several points off (depending on the mix) if measured right after finishing a fill, but right on after a couple hours.

That's probably a big part of the difference. I will shoot for about 50-60 psi/min for the O2 but will then top off the last 1900 psi with air in 5-6 minutes (in a smaller 30 or 40 cu ft deco bottle) so there is probably a lot more mixing occurring immediately in the tank.

 

[m3830431]

IF I recall the PADI EANx class suggest that rolling may have to be done with certain blending configurations (ie equipment) the places I go do not require self mixing and I haven't been to one that does.

 

[MXGratefulDiver]

Sooooooo.. its not like a Black and Tan? Black being Oxygen as it is heavier according to the periodic table, Tan being Nitrogen as it is lighter? Given time the black will mix with the tan but on a slow mix it will take a while as the specific gravity of Bass is also slightly lower than Guinness (4% for Bass vs. 4.2% for Guiness). Of course this is the prescribed mix from Guinness promotional advertising and was posted as the correct mixture on the 1759 Society charter members website a few years ago.

Will the Black (actually its dark red but thats a moot point) actually mix with the tan? Yes, when left to sit and settle the black will mingle in with the tan and sooner or later you get an interesting reddish and very flat beer. Will O mix with N if you let it sit a while.. yup.. it just takes a while.. well, it doesn't if you dont use the spoon and just let the tan blast into the black then you get it pretty close to what it will be if you trickle into the glass slow.

Whatever you do, don't roll the Black & Tan around the bar in the glass.. its very messy and a waste of perfectly good BEvERage.

Or better yet, put the beer in a pressurized container at, oooooh say, 200 ATA or so ... add a touch of heat ... and see what happens ...

... Bob (Grateful Diver)