Rebreather World - View Single Post - Why does depth matter for scrubber lifetime

silent running · 2nd November 2007, 07:32

Quote: (Originally Posted by Abbo)

I would be interested what the real time to breakthrough would be under equivalent conditions with the same mass of scrubber in an axial. The figures seem broadly in line with commments that times are 150% to 200% of those for an axial.

I hazily recall a graph of FCO2 over time for an axial and radial, though I have no idea how to track it down. If you are right I certainly can't visualise the physics that would account for it.

Hi Abbo, the NEDU tests of the Prism scrubber list the average breakthrough to .5% surface equivalent value as 255 minutes at 1.35 slpm of CO2 with a 40 lpm RMV, continuos. Then 283 min to 1.0% SEV and 306 min to 2.0% SEV. So it takes 28 then 25 minutes respectively, at a reasonably high RMV and CO2 flow to double the CO2% in the loop.

While I wouldn't call this average of 26.5 minutes at a high flow to reach double the CO2 a really slow breakthrough, it certainly doesn't seem so fast to either.

I think I understand the idea behind the different breakthrough characteristics of axials and radials, but in an in-out flow radial the gas flow slows as it reaches the outside and the dwell time increases and so does the chance that the CO2 will react with whatever unused sorb is left. There should always a greater portion of unused sorb on the outside of an in-out flow radial and a slower gas velocity, thus the not so drastic breakthrough.

I tried to imagine what the opposite flow out-in radial breakthrough characteristics would be given the opposite effect-faster gas flow as the surface area narrows and finally reaches the narrow, inner tube-yikes...

2nd November 2007, 07:32	#39 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,873	Re: Why does depth matter for scrubber lifetime Quote: (Originally Posted by Abbo) I would be interested what the real time to breakthrough would be under equivalent conditions with the same mass of scrubber in an axial. The figures seem broadly in line with commments that times are 150% to 200% of those for an axial. I hazily recall a graph of FCO2 over time for an axial and radial, though I have no idea how to track it down. If you are right I certainly can't visualise the physics that would account for it. Hi Abbo, the NEDU tests of the Prism scrubber list the average breakthrough to .5% surface equivalent value as 255 minutes at 1.35 slpm of CO2 with a 40 lpm RMV, continuos. Then 283 min to 1.0% SEV and 306 min to 2.0% SEV. So it takes 28 then 25 minutes respectively, at a reasonably high RMV and CO2 flow to double the CO2% in the loop. While I wouldn't call this average of 26.5 minutes at a high flow to reach double the CO2 a really slow breakthrough, it certainly doesn't seem so fast to either. I think I understand the idea behind the different breakthrough characteristics of axials and radials, but in an in-out flow radial the gas flow slows as it reaches the outside and the dwell time increases and so does the chance that the CO2 will react with whatever unused sorb is left. There should always a greater portion of unused sorb on the outside of an in-out flow radial and a slower gas velocity, thus the not so drastic breakthrough. I tried to imagine what the opposite flow out-in radial breakthrough characteristics would be given the opposite effect-faster gas flow as the surface area narrows and finally reaches the narrow, inner tube-yikes...
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