Dummy question for clever people.

[Digger]

With nidies can't you just use a decanting whip and leave them for a while? Failing that you could use an old twinning bar. I got one free with some old tanks which would basically act as a manifold, without me having to do any nasty manifolded diving.

[Fiona]

Originally Posted by [b

Quote[/b] (spike jackson @ Nov. 08 2003,17:10)]I did one dive in Scapa on indies with 34% in one cylinder and 38% in the other - meaning I would have had a pO2 of 1.7 at max depth. So I had to treat the richer tank as deco and travel gas.

<font color='#0000FF'>Spike

Did you want two separate mixes or did you ask for the same ? &nbsp;If you wanted them both the same you should have asked them to be re-done. &nbsp;They should be within +/- 1%.

Fiona

[Jay]

Originally Posted by [b

Quote[/b] (Finless @ Nov. 09 2003,22:25)]

Well - I was hoping for a really definitive answer involving molecular weights and chaos theory - just to brighten up my Friday afternoon you understand.

Ok - saying no one else is biting, the second law of thermodynamics dictates that, if you fill one cylinder with O2 and the other with air and leave you manifold open, you will eventually end up with an even nitrox mix in both cylinders. Happy?? &nbsp;

[Finless]

Originally Posted by [b

Quote[/b] (Heads Up @ Nov. 11 2003,08:04)]Ok - saying no one else is biting, the second law of thermodynamics dictates that, if you fill one cylinder with O2 and the other with air and leave you manifold open, you will eventually end up with an even nitrox mix in both cylinders. Happy??  

Heads Up,

Almost happy - is it possible to quantify &quot;almost&quot;? (Your almost that is, not my almost).

Rgds
Bryan

[Rupert Bear]

Originally Posted by [b

Quote[/b] (Heads Up @ Nov. 11 2003,08:04)]Ok - saying no one else is biting, the second law of thermodynamics dictates that, if you fill one cylinder with O2 and the other with air and leave you manifold open, you will eventually end up with an even nitrox mix in both cylinders. Happy??  

But it would take a LONG time. The small CSA of the hose would stop diffusion of oxygen between the cylinders happening very fast, I would take a rough guess and say it would take days to weeks to equalise the mixes and they would in practice take months to be completely equal.

[Jay]

Originally Posted by [b

Quote[/b] (Finless @ Nov. 11 2003,10:50)]

Heads Up,

Almost happy - is it possible to quantify &quot;almost&quot;? (Your almost that is, not my almost).

Rgds
Bryan

My 'almost'? Didn't use one. The second law of thermodynamics describes the desire in nature towards entropy (not chaos). It begins by telling us that energy can only flow from hot to cold and not vice versa and this, in turn, explains how gas molecules will naturally seek a position of equilibrium. Different gas molecules will 'collide' or oscillate at different speeds and thus will 'generate' different levels of energy in the form of heat. In a large room, if one half was filled with pure O2 and the other was filled with pure N2 then each side of the room would initially have differing temperatures. Given that energy cannot be created or destroyed and given that energy can only 'flow' from hot to cold, the different gasses would seek a common levels (by mixing) and therefore stopping the flow of energy from one side to the other - a natural balance. Therefore the initial scenario of diffused gases has now 'entropied' or irreversibly broken down and the gas is evenly mixed.

Given the size of a gas molecule compared to the diameter of a manifold, the time taken for this to happen would be quite a bit quicker than imagined - certainly not weeks.

BTW, to all scientist's who are wincing at my (probably widely inaccurate) description, I'm a financial services manager with an O level in physics who has a passing interest only in this sort of styff so don't jump on me from too high please

[Rupert Bear]

There would be a gradient between both tanks as they tried to reach equilibrium. This would be high at first but would slow down considerably as the gradient flattened out. The area where the exchange can take place is also quite small.
Without experimentation there is no way of telling for sure but i wouldn't rely on it being very fast, especially as the two mixes started to get close.
&nbsp;My guess is still days to weeks for reasonable equalisation although my experiments admittedly with this type of O2 question normally involve it dissolved in water and that is extremely slow.

[Finless]

Originally Posted by [b

Quote[/b] (Heads Up @ Nov. 11 2003,16:34)]My 'almost'? Didn't use one.

Apparently I have the attention span of a gold fish - I think I substituted &quot;eventually&quot; with &quot;almost&quot;. Must get the high protein Tetra-Min to see if that improves my memory.

[Jay]

Like I said, this is not my field of expertise. (Do I win the prize though Finless?)

[Janos]

I ought to know this. I did once (I've got a degree in physics somewhere but too little use and too much alcohol have rotted it away). Something to do with Kinetic Theory and mean free paths.

I'll try and dig out my notes and do a few sums, but I may be some time. Better off getter doing a practicing physicist to do the job. Any around?

Laters,
  Janos