How a diving carbon dioxide absorber works article question

wedivebc

Based on the very unscientific evidence that the warmest part of the scrubber seems to be just above the purple zone I have always assumed the purple is mostly used and not as active as the scubber just past it.

__________________
Cheers,

Dave....

Man is the only animal burdened with the knowledge he will eventually die

onetime

I get the dwell time but I was wondering just how much dispersion of gas within the sorb column would occur in tightly packed scrubbers between breaths.

The fact that the absorption takes place through the entire "grain" as both zzzzzzzz and you have said changes my thinking quite a bit but I still tend to think that there is some % of unreacted sorb in a canister that's at the breakthrough point. I wonder if there have been any studies on just how much (goes towards scrubber efficiency).

Freef

http://www.rebreatherworld.com/semi-...tml#post124311

I dug out my scrubber with a spoon after a days diving and the posts 1 & 4 on the above show the results.

Apparently a Submatix has more of a 'core' penetrating through the centre of the scrubber [defeats the objective of the transparent cannister and colour changing sorb a bit!].

I wouldn't turn a scrubber around as you wouldn't get a lot more use out of it. The gas travelling past the grains doesn't leave a shadow where it doesn't interact in some way with them, and while not all the grain may be used, it wouldn't be a known fact as to how much life there was left.

The warm spot in a scrubber is an indication of where the reaction front is. I found that the Drager Divesorb gives a very [1 inch/25mm] small band that is easy to track and 797 gives a broader band. I have only used Spherasorb a couple of times, so I can't remember how that fared, but I think that it was fairly diffuse.

__________________
David.

Currently owner of two differently sized ankles.

onetime

The "turn the scrubber around idea" was based on if it was surface area reacting to CO2 so that gets nixed by the "throughout the grain" reality.

I've got to imagine the diffusion is fairly dependent on body position during the dive. If most time is spent horizontal diffusion would be one way, if mostly vertical another, if half and half perhaps more equal? I don't know just thinking out loud here.

Freef

The Dolphin scrubber is horizontally mounted and I couldn't see any difference in the 'top' and 'bottom' parts of the scrubber. With the gas flowing through the loop, I doubt whether the angle of the scrubber has any appreciable effect on duration or efficiency. Could be wrong though!

__________________
David.

Currently owner of two differently sized ankles.

onetime

To give some heft to how I'm imagining it in my mind, I'm thinking of the gas acting similarly to a liquid in terms of tipping. Although the gas would move in the opposite direction as would a liquid. e.g., when the canister is tipped more upward the liquid would find the lower crevices more appealing for a path where a gas would find the upper crevices more appealing. Not that this line of thinking is going anywhere particular but you never know what obscure thinking will result in.

teomannaskali

I think that reversing the cannister is not a good idea. Because:
1. When you consider "used sorb" that is not actually completely used, it is mostly used and it still has a little ability to scrub except not as fast. Antoher thing that I think that affects its scrubbing ability is the concentration of the CO2. The more co2 there is the more chance of catching some of it...

So if you reverse the scrubber then the still fresh part of the scarbber catches the co2 and the alredy spent part that still has just a little capacity has to perform with less efficiency because it receives almost CO2 free gass. And when indeed the fresh part also becomes depleted the used part is not enough to scrub.

On the other hand. If your scrubber is not efficient and the gas does not flow uniformly then reversing the flow might enable you to access parts that would not be normally accessed with standard usage of that scrubber model. With a good design this should/could not happen of course.

This is just what I think and I have no real experience on the matter.

Teoman

teomannaskali

To the best of my training and knowledge that is not how things work unless you have a partially flooded scrubber. With your line of thinking (gas is a fluid -> water) you should imagine that the cannister is completely flooded with the liquid that you model as a gas.

Like in reality if there is water in the scrubber it will prefer the bottom parts and the upper parts will be left to the gas. But if it is filled with gas, the only thing that prefers the upper parts would be a less denser gas like helium or vaccum pockets. But neither are possible bacuse the gasses mix pretty well inside the loop and gasses expand so any vaccum pockets or anything is not possible.

Teoman

Freef

You appear to be mixing up 'liquid' with 'fluid'.

A fluid will attempt to take the shape of the container-liquids do this but are held to the bottom by gravity, and gasses do it more effectively. If you blow a balloon up, no matter what way you tip it, there won't be an 'empty' part of the balloon because the gasses will fill it equally. While O2, N2, He and CO2 are of different densities they get well mixed in the loop and can be consideed pretty much uniform by the time they hit the scrubber

The original Rebreather's were O2 and had a 'pendulum' CL and scrubber. The loop went into a scrubber and then into the counterlung-there was only one-and when the diver inhaled the gas passed back through the scrubber into the loop.

While it is still possible to design a pendulum Rebreather, the increase in scrubber duration would be minor, and there is a lot larger 'dead air' space in the loop than on the RB's we use with two lungs and a non reciprical flow through the scrubber.

Attached Images

pendulum.JPG (9.2 KB, 126 views)

__________________
David.

Currently owner of two differently sized ankles.

onetime

Not mixing them up at all just didn't have a better description. The problem with the balloon analogy is that there is nothing impeding the flow of gas within the balloon. In a scrubber you've got absorbent. Some paths through the absorbent will be easier than others. That's where I'm thinking "flow" comes in with regard to the tipping or changing direction of the higher CO2 gas.

In any event it's just ponderin'.