Gettiing to 32%

[RJP]

.

in post 2 i said it was a theory.
just kick it around and see what happens.

I'm kicking it as hard as I can... :d

I may need to go to the shop tomorrow and test a few things out on the fill station.

 

[Akimbo]

...Is there something in the tank that moves the molecules around when the tank is rolled? ...

Yes. The interior surface of a cylinder is rough (small grooves from the deep-drawing process) which causes turbulence when rolled.

You get the most stratification when changing mixes, like topping off air with a Nitrox Mix or partial pressure blending. You should not get significant stratification starting near empty using continuous blending or membrane systems.

 

[altaskier]

OK, this got me curious so I decided to do a rough calculation. The result surprised me! It takes around 10 hours for a gas molecule to travel halfway across the diameter of an aluminum 80 cylinder if it is due to diffusion alone. I would have thought that a stratified gas mixture would equilibrate much more quickly than that, but the molecules are pretty crowded in a full tank.
http://xrm.phys.northwestern.edu/~jacobsen/diving/scuba_tank_gas_diffusion.pdf
Of course this calculation ignores anything else that might go on, like turbulent mixing from rolling a cylinder.

A few other comments:

• One doesn't need a rough surface to cause mixing by rolling a cylinder. There are adhesive forces between molecules and surfaces and molecules to each other, and also rotational inertia to the gas. Adding imparting rotational inertia to the outside molecules will lead shear forces in the gas and thus mixing. This is a well known phenomenon in fluid dynamics.
• It's not so plausible to get an oxygen concentration on the outer walls of the tank from rolling them quickly. There's about a hundred thousandfold difference between thermal energy and gravitational potential energy across a tank radius, so you'd have to spin the tank mighty quickly (like to a centrifugal force of 10^5 g) to overcome thermal diffusion.

 

[kwinter]

I may need to go to the shop tomorrow and test a few things out on the fill station.

Fill one standing up and one lying on its side. I'd be very interested in the results.

 

[Peter69_56]

And all I wanted was a Nitrox mix of 32% Mister.

"I see" said the blind man, but he didn't.

Is the glass half full, or half empty - more to the point, does it really matter? Well to the ant in the glass it sure does! It all depends on your perspective.

 

[BluewaterSail]

What do you rollers and shakers do with your doubles?

 

[Dive-aholic]

What do you rollers and shakers do with your doubles?

If you dive doubles you need to be strong enough to pick them up and shake them up...

 

[RJP]

If you dive doubles you need to be strong enough to pick them up and shake them up...

Easy enough with my double AL80s. A set of steel HP119s are another issue altogether...

 

[boulderjohn]

Easy enough with my double AL80s. A set of steel HP119s are another issue altogether...

I just take my double steel 108s and shake them like a martini shaker--don't you?

 

[Searcaigh]

wear them and a do a few back flips