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Alec,
I'm tending toward having the fans draw the air through the scrubbers
rather than push it. I think that might make it easier to design for even
airflow through the material. It also makes it easier for the
fans to be located nearer my feet instead of near my head.
I would think the scrubbers could be subject to degradation from moisture
intrusion or some other causes I'm not aware of, so I'm planning
redundancy there, too. The question I have is if it would be
prudent/practical to install a filter/water trap upstream. Hopefully that could
be done without significantly impeding airflow. This brings up the related
topic of humidity control in the sub in general.
Comments?
Thanks,
Jim
In a message dated 3/14/2011 4:53:04 P.M. Central Daylight Time,
Alec.Smyth@compuware.com writes:
Excellent points gentlemen, thanks. I had initially mounted the
fans to
blow into the center cylinder, but will now reverse them based on
Sean's
suggestion. Note I say "fans" because I'm mounting two of them
in
series, for redundancy, although only one would normally be used.
The
scrubber itself has no moving parts, so I figure the fan is all that
can
fail.
Cliff, I agree squirrel cage fans would be a better choice
from a
performance perspective. However, I'm so tight on space that I'm
at
least giving axial a try before discarding the idea. Also, Deep
Worker
uses axial. Note I'm not shooting for 72 hours, and because Snoopy
has
12V main propulsion, the whole boat runs off one big battery bank
so
current draw should not be an issue. I'll have to see about the
pressure
and noise. I've convinced my daughter to join me in Snoopy for
some
hours, so we can make it a two person test. However, I am still
awaiting
delivery of the fans, which should be here any day.
Jon,
the photo you linked to looks functionally identical to the eBay
filters,
except the end pieces are plastic while these are aluminum. The
thickness
of scrubbing agent is about 2". The one I'm using is eBay
item
#400187881680.
I'll report back
post-test.
Alec
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From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]
On Behalf Of Sean T.
Stevenson
Sent: Monday, March 14, 2011 4:01
PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] open
source scrubber design
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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