Re: [PSUBS-MAILIST] open source scrubber design

["Sean T. Stevenson" <cast55@telus.net>]

The scrubber is a radial flow design, with the flow direction from the outer 
diameter to the inner one.  This makes most efficient use of the scrubber 
material, as the flow area is greatest at the outer diameter when the gas 
contains more CO2, and reduces as you approach the inner tube, as CO2 is 
removed.  Also, the inlet flow area of the scrubber (outer diameter x pi x 
length) is huge in comparison to the minimum scrubber inlet diameter, making 
the velocity (assuming even pressure distribution) almost nil through the 
absorbent.  One thing to be wary of when comparing submersible scrubbers to 
rebreather scrubbers, is that the gas flow through the rebreather device is 
cyclic - there is a very small pressure differential between the gas in the 
exhale counterlung and the gas in the inhale counterlung, which leads to slow 
gas movement through the scrubber - the "dwell time" of gas inside the 
scrubber is only interrupted when the inhale counterlung collapses and gas 
must be drawn through.  Submersibles, on the other hand, must use steady flow 
and so the gas velocity through the material must be accounted for - of 
course, you can make up for higher speeds with more passes, but the least 
noise and power consumption solution is a slow flow through a large device.

-Sean


On Monday 14 March 2011 12:12:54 you wrote:
> Alec's test results will be very interesting to follow.  These canister
> units, if I understand the way Alec intends to use it, are a radial
> design.  One of the potential problems I see is that there is only 1-1.5
> inches of material in the void between the canister walls which makes me
> question whether that will provide adequate "dwell time" for the CO2 to
> pass over the material and be absorbed efficiently.  It will also be
> interesting to hear from Alec how difficult the units are to pack with
> material.
> 
> Alec, depending upon your results I would also look a modifying the can
> somewhat by adding a center tube, maybe 1 inch in diameter through the
> axial center of the can (like this
> http://www.flickr.com/photos/billreals/2966584447/ ).  Add sodasorb into
> the interior (and between the canister walls if you want) and feed the
> air flow through the center tube via a centrifugal fan.  This would
> allow more dwell time through more material.
> 
> Jon



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