Reading the Tea Leaves/Sodasorb Grains

jkaterenchuk

Yes I was wearing stages in each case...either 2x40 or 2x80 always one on each side.

John

Hk101gr

I think this is an important observation.
The side of the can where the exhaled gas enters would always be warmer then the the rest of the can. So we can reasonably assume that the scrubber on that side gets warmer then the rest and the color uneveness is a case of more-less efficient scrubber reaction.

This can be easily confirmed on a rig with a neoprene can cover or one of those sprayed with truck bed coating.
Just a thought

Dive safe
Dimitris

Padipro

Hk, you're hitting on a question I was thinking throughout this thread and no one has really mentioned. Is the loop covered with protectors or the canister coated with any bed liner? This may insolate the canister and loop changing the internal temperature in certain areas of the breathing loop causing the difference in the color pattern.

FWIW...I have an after market radial scrubber and have seen the color change that was perfectly even all the way around the curcumferance of the scrubber nearly dividing the scrubber in half. The bottom half of the scrubber was dark purple and the upper half was still white. One would think that in a radial scrubber the color change would cover the entire outside surface and work it's way to the center. But I'm an aircraft mechanic so what do I know about CO2 scrubbers.

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bobby

Interesting thread and the pictures add a lot. I think though that looking at the color change as an indicator of sorb usage may be misleading. You have set up good structure in the evaluation to get consistent results. This shows that the color change is not random and probably confirms that you are packing consistently. On the other side though I don't know if color change relates to used sorb.

One thing that I have found is that the bottom of the scrubber consistently has the most color change. This includes a third or fourth dive on the same can that should in theory have the middle of the can changing color and not the bottom since the bottom of the can has already been used. This leads me to believe that the color change is a thermal reaction independent of CO2 absorption. Just a thought.

I believe your results show this to be true. Flow dynamics dictate that an axial scrubber will flow in a cone pattern from widest at the entry to smallest at the top. With the area that your second set of pictures shows purple on the top of the scrubber you should have been right at or past break through, wit the center being more dense in CO2 absorption than the outside. If heat was the driver though for the color change, independent of CO2 absorption, then the fact that you had color change past 50% off the base would not indicate break through.

Bobby

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jkaterenchuk

Scott

Normal outside Movie Meg canister without any coating or protector. Also bare loop hoses.

John

jkaterenchuk

I was really hoping that someone that is well versed on both scrubber design and absorbant chemistry might have commented. Maybe this person does not exist.

Anyways, no signs of scrubber breakthru on any of these dives based upon my past experience with elevated rate of breathing as the first and main symptom.

John

jkaterenchuk

You might be right but what evidence can you point me too read that clearly supports your comment that the exhaled gas will always be warmer then the rest of the can?

As I think about it I am not sure that make sense to me as the exhaled gas will be basically at body temperature when it leaves my mouth and then cools from there while it travels thru the loop and enters into the CO2 absorbent. Since the CO2 absorbent reaction is exothermic I suspect that the temperature produced by this reaction is higher than body temperature and hence the gas that left my mouth would be heated as it travels thru the scrubber material and is subjected to area in which the reaction is occuring.

Of course this would not be the first time that my thoughts would be completely wrong.

John

Scubascooby

I wonder if the reaction is that exothermic ? Obviously the amount of heat produced is a function of CO2 absorbed but is it enough to heat it above the temperature of the exhaled gas that has cooled while passing to the scrubber ? All this is dependant on the heat balance of the scrubber, ie how much heat it loses compared to heat received in the gas and generated by the chemistry.

I don't know, I am just asking the questions. Molecular Products probably know the answers.

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jkaterenchuk

I have never measured the temp. But when I took the scrubber cannister out immediately after the dives to take the pictures in this thread it felt hotter than body temp. Not to hot to touch but quite noticeable.

Here is a quote from a interesting article posted by Grace the makers of Sodasorb related to reaction temp.

"Exothermic Heat Generation

The chemical reaction of carbon dioxide with a strong base such as Sodasorb is exothermic, the heat of neutralization amounting to 13,500 calories with the absorption of each gram molecular weight of carbon dioxide (44 grams or 22.4 liters). This heat is not evenly distributed throughout the canister because the reaction itself is zonal. For example, it was demonstrated by Adriani and Rovenstine that in the canister of a to-and-fro apparatus the temperature was in the range of 50° to 55°C at the center of the absorber canister, but 5°C lower towards the bag end of the canister and 5°C higher towards the face mask. The face mask temperature range was from 39° to 42°C.

Heat of reaction does not appear to affect absorptive efficiency, although rising temperature within the canister indicates that carbon dioxide absorption is proceeding. Some of the variables affecting heat generation are the patient’s rate of carbon dioxide production, body size, metabolic rate, body temperature, and the ambient air temperature in the operating room."

Here is a link to the thread were you can view the complete article.

http://www.rebreatherworld.com/scrub...absorbent.html

John

jkaterenchuk

Picked up this information on the colour change from the Grace site.

"Absorbent Exhaustion Indicator

To signal the progressive exhaustion of Sodasorb absorbent, ethyl violet color dye (a sensitive acid-base indicator) is added during manufacture. Indicator Sodasorb changes from white to purple as absorption proceeds, full exhaustion being indicated by a deep purple color. Presence of the indicator does not affect absorption.
It should be noted that since the neutralization reaction is not uniform throughout the canister, color change is also not uniform. The zone of greatest reactivity in a circle apparatus canister is largely at the inlet end and in a parabolic central cone. The color of the exhausted absorbent showing through the transparent wall of the canister, or through the inspection window, requires experience for correct interpretation.
Intermittent use of the Sodasorb absorbent must be taken into account, since it may

Ethyl violet is a particularly effective indicator for use with Sodasorb absorbent, its critical pH being 10.3. As the strong caustic sodium hydroxide (NaOH) is consumed and is replaced by the weak base calcium hydroxide, the color change parallels the falling pH in the canister. The color change is usually sharp enough to be conspicuous even under difficult lighting conditions. "