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Re: [PSUBS-MAILIST] scrubbers
Ta Jon,
Didn't realize the computer fans pushed so much air.
I have an 80mm fan & sofnolime, so will check the
flow through the absorbent.
Was reading in the sodasorb manual that humans produce 4ml
of CO2 per kg of body weight. So I guess weight is another
variable to factor in.
Alan
----- Original Message -----
From: "Jon Wallace" <jonw@psubs.org>
To: <personal_submersibles@psubs.org>
Sent: Monday, June 14, 2010 5:18 PM
Subject: Re: [PSUBS-MAILIST] scrubbers
Alan,
Here's a photo of the DW2000 scrubbers.
http://www.psubs.org/convention/2009/photos/pics.cgi?jonw/DSCN0778.JPG
A 160 liters/minute airflow is pretty low velocity. Your typical 80mm
computer fan is pushing about 840 liters/minute. I can tell you from
personal experience that the airflow coming out of the scrubber fans of
the DW2000 is so low velocity that you have to put your hand as close as a
few millimeters from the fan blades to feel it. While I was waiting for
the crane to lift me into the water (with the hatch closed) one of the
things I noticed was the lack of fan noise that I expected from the
scrubbers, so I put my hand down to the fan and sure enough it was running
but the air velocity was surprisingly minor. Also, while the fan might
have been rated at 160 liters/minute in open air, the soda lime is going
to cause friction on the air and slow it down as it travels through the
scrubber (hence you get your dwell time).
There's only so far you can get with raw numbers when it comes to
scrubbers. The variables involved in totality of the design require
practical testing with either lab equipment that can measure air flow and
chemical content, or in the finished sub (on land, NOT in the water) with
an O2 and CO2 meter to see how it performs over time.
Also remember that the effective capacity of your scrubber is not going to
be the volume of material you put in it, due to "chemical saturation"
(slide 12 in my online slide set).
Jon
Alan James wrote:
To All,
While looking at various papers on CO2 scrubbers from manufacturers
etc, I found that none addressed the unique situation found in
submarines.
Most CO2 absorbent is used in anesthetic machines or rebreathers where
there is a closed circuit. The CO2 breathed out goes straight into the
scrubber
& is removed.
In our subs the CO2 is breathed out & is diluted by the rest of the air
in the
hull & only air with a portion of the CO2 in the hull goes through the
scrubber.
This means that the CO2 level & the pressure in the hull will
progressively climb
unless the volume of air going through the scrubber is large enough to
make an
impact. The Deep Worker 2000 has fans pushing 160 liters per minute, I'm
not
sure whether this is per scrubber & whether they have 2 scrubbers working
simultaneously. But based on 1 fan going, that's 320 x the volume of CO2
being
produced. In the manufacturers guidelines for scrubbers they recommend
that the flow
is at least equal to the tidal volume of your breath (about 10 liters per
minute)
& low enough so that the air has at least 1/2 a second dwell time in the
canister.
This could be 32 x less than what Phil has worked out is necessary for
the
Deep Worker. I know the Deep Worker has a small hull & that fluctuations
in O2
& CO2 are more critical than a K250, but possibly the same volume of flow
is
necessary to achieve atmospheric control in larger subs.
Also because of the dwell time needed the large flow required would need
large or
long canisters. Deep Worker has 2x 3.35 kg scrubbers.
On the psub site there is reference to rebreather cartridges as an
option, but from
what I've found you would probably need a number of these running
simultaneously
to make head way.
What are ABS recommendations? & what are others thoughts / experiences
with this.
I'm trying to sort this stuff out for myself.
Regards Alan
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