Rebreather World - View Single Post - Chemistry of CO2 Neutralisation - Can weight be used as an indicator of scruber life?

diveoceanos · 1st April 2008, 16:24

Hello Jaap,

Since there have not been any data so far how one can be so sure that the approach is a waste of time? I would say that the maximum loss in case the outcome will be inconclussive is a waste of time recording several hundreds of dives and analyse them. No?

I see your point and scepticism! This is not definitely without a base but on the other hand is a little dogmatic. Why shall this approach be considered and treated as a taboo? There has not been any suggestion to ignore what is being allready used. And that is manufacturer's reccommendations. We keep doing what we do and at the same time we accumulate some data for the sake of analysis. There is an hypothesis and this hypothesis should be tested to be confirmed or rejected! That's all.

A few thoughts about your interesting post below:

Quote: (Originally Posted by jaap)

I would say your way of looking at the scrubber chemistry is incorrect. My understanding is that the strong base is not consumed one way but that it is continously reformed as long as there is sufficient Ca(OH)2 present (and temp, humidity).

I have only one drawback with the suggested chemistry that is being around for quite a long time now. And this is simply based on very basic principles in chemistry. A salt of strong base (Na2CO3) if put together with a weaker base (Ca(OH)2) would definitely not regenerate the strong base. This would form a buffer system but the very details of this are going beyond the purpose of the suggested experiment. Perhaps I am completely wrong here, since I took my chemistry lessons back in 1995 when I was a student in Pharmacy

. Those principles have been around for centuries but yes my approach might be wrong since things are changing over time and i might have lost track of chemistry evolution. Any other opinions by other folks?

Quote: (Originally Posted by jaap)

I don't think the weight approach is neither safe nor practical or even informative of the state of the scrubber.

For the time being the suggestion is to put this under investigation before we end up with a conclussion like the above.

Quote: (Originally Posted by jaap)

OK, considerable amounts of water is formed during the scrubber reaction, but some is added from the users lungs, some could also be introduced from the outside from leaks. How do you determine these fractions?

Some of that water can also end up in basically every part of the unit depending on how the diver moves around and on the water/loop temp. Would you then collect all this water?

All correct here! But remember that the suggestion is to study just the scrubber cartridge, not the system as a whole! The less water is adsorbed or condensed inside the cartridge the better the conditions for the experiment are going to be. Actually we want to get rid of the excess water. We are not aiming at weighting every single droplet in the system. We don't actually care about how much water there is in the system. What we care is the weight change in the sorb itself. We are also hoping that the water quantity in the sorb will be minimal or constant percentage (well more or the less) of the weight change. Anyway this has to be shown with real measurements.

Quote: (Originally Posted by jaap)

Finally what is the point with this thing? It would still not say anything about the reaction path inside the scrubber. To me the total scrubbing capacity of the scrubber is not very interesting unless you also have information on the profile of CO2 penetration and reaction path. A scrubber could still have alot of remaining scrubbing capacity while being completely unusable (especially at depth/high workload) due to an intolerable breakthrough of even a
comparatively small fraction of CO2.

Remember the experiement is to test the parameter weight and how does this relates to scrubber life. We have for instance known starting points. What are those? Scrubber life of axial scrubber in a Meg for instance has been proposed to be good for 4 hours at 0 degrees with a CO2 flow of 4LPM. This can resemble virtually any level of work load at any depth. Correct? Or shall we decrease that in 3,5 hours? Would you feel more confortable with this? Let's start and then take it from there. If we measure the weight change for all these 4 hours (or 3,5) then we can check how weight can be related (or not) with scrubber life. No? And then if eventually we end up with a conclussive otucome we are going to have an extra point to check scrubber life or some nice story to tell to our children about an experiment that proves that weight is neither safe nor informative about the life scrubber.

Quote: (Originally Posted by jaap)

So as long as CO2 sensors remain elusive in rebreathers I think empirical rules of thumb, the temp sticks and pH indicating dyes are the only things that are practical and give some degree of guidance.

BTW, the dye used in some sorbs actually gives a measure of the remaining strong base and the distribution of the used material. So as far as I can see that method (with its limitations) is already superior to any field attemps to use weight to measure scrubber life.

Nice point above! Remember that the suggestion is to test an hypothesis! Not to erase what is being allready used in daily practice!

Cheers!

Sotos

1st April 2008, 16:24	#20 (permalink)
diveoceanos New Member Current Rebreather/s: Megalodon Other Rebreather/s: Join Date: Apr 2007 Location: Cyprus Posts: 43	Re: Chemistry of CO2 Neutralisation - Can weight be used as an indicator of scruber l Hello Jaap, Since there have not been any data so far how one can be so sure that the approach is a waste of time? I would say that the maximum loss in case the outcome will be inconclussive is a waste of time recording several hundreds of dives and analyse them. No? I see your point and scepticism! This is not definitely without a base but on the other hand is a little dogmatic. Why shall this approach be considered and treated as a taboo? There has not been any suggestion to ignore what is being allready used. And that is manufacturer's reccommendations. We keep doing what we do and at the same time we accumulate some data for the sake of analysis. There is an hypothesis and this hypothesis should be tested to be confirmed or rejected! That's all. A few thoughts about your interesting post below: Quote: (Originally Posted by jaap) I would say your way of looking at the scrubber chemistry is incorrect. My understanding is that the strong base is not consumed one way but that it is continously reformed as long as there is sufficient Ca(OH)2 present (and temp, humidity). I have only one drawback with the suggested chemistry that is being around for quite a long time now. And this is simply based on very basic principles in chemistry. A salt of strong base (Na2CO3) if put together with a weaker base (Ca(OH)2) would definitely not regenerate the strong base. This would form a buffer system but the very details of this are going beyond the purpose of the suggested experiment. Perhaps I am completely wrong here, since I took my chemistry lessons back in 1995 when I was a student in Pharmacy. Those principles have been around for centuries but yes my approach might be wrong since things are changing over time and i might have lost track of chemistry evolution. Any other opinions by other folks? Quote: (Originally Posted by jaap) I don't think the weight approach is neither safe nor practical or even informative of the state of the scrubber. For the time being the suggestion is to put this under investigation before we end up with a conclussion like the above. Quote: (Originally Posted by jaap) OK, considerable amounts of water is formed during the scrubber reaction, but some is added from the users lungs, some could also be introduced from the outside from leaks. How do you determine these fractions? Some of that water can also end up in basically every part of the unit depending on how the diver moves around and on the water/loop temp. Would you then collect all this water? All correct here! But remember that the suggestion is to study just the scrubber cartridge, not the system as a whole! The less water is adsorbed or condensed inside the cartridge the better the conditions for the experiment are going to be. Actually we want to get rid of the excess water. We are not aiming at weighting every single droplet in the system. We don't actually care about how much water there is in the system. What we care is the weight change in the sorb itself. We are also hoping that the water quantity in the sorb will be minimal or constant percentage (well more or the less) of the weight change. Anyway this has to be shown with real measurements. Quote: (Originally Posted by jaap) Finally what is the point with this thing? It would still not say anything about the reaction path inside the scrubber. To me the total scrubbing capacity of the scrubber is not very interesting unless you also have information on the profile of CO2 penetration and reaction path. A scrubber could still have alot of remaining scrubbing capacity while being completely unusable (especially at depth/high workload) due to an intolerable breakthrough of even a comparatively small fraction of CO2. Remember the experiement is to test the parameter weight and how does this relates to scrubber life. We have for instance known starting points. What are those? Scrubber life of axial scrubber in a Meg for instance has been proposed to be good for 4 hours at 0 degrees with a CO2 flow of 4LPM. This can resemble virtually any level of work load at any depth. Correct? Or shall we decrease that in 3,5 hours? Would you feel more confortable with this? Let's start and then take it from there. If we measure the weight change for all these 4 hours (or 3,5) then we can check how weight can be related (or not) with scrubber life. No? And then if eventually we end up with a conclussive otucome we are going to have an extra point to check scrubber life or some nice story to tell to our children about an experiment that proves that weight is neither safe nor informative about the life scrubber. Quote: (Originally Posted by jaap) So as long as CO2 sensors remain elusive in rebreathers I think empirical rules of thumb, the temp sticks and pH indicating dyes are the only things that are practical and give some degree of guidance. BTW, the dye used in some sorbs actually gives a measure of the remaining strong base and the distribution of the used material. So as far as I can see that method (with its limitations) is already superior to any field attemps to use weight to measure scrubber life. Nice point above! Remember that the suggestion is to test an hypothesis! Not to erase what is being allready used in daily practice! Cheers! Sotos
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