Yes and no..
The problem is more that if you have a large air volume you have
blow a lot of more air into your scrubbers to get the amount of co2 out.
On a small one man sub the co2 level raised quickly - but goes down also
quick down with running scubber.
On a bigger volume sub with the same scrubber and same one person you have
to run the scrubber much longer to catch all the co2 atoms in the large
volume of air..
To give you an surreal picture: Imagine a Hindenburg Airship big
submarine. Inside one man with a one man scrubber. It will takes maybe
years before the co2 inside level raise to high - but it will takes
also years for the filter to get it out..
vbr Carsten
"Land N Sea" <landnsea1@hawaiiantel.net> schrieb:
I would think it would as the larger the air volume for a person to
breath, the longer it would take to drop the C02 level to an unacceptable
level before needing to scrub??
From: JimToddPsub@aol.com
Sent: Sunday, March 13, 2011 10:35 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] open source scrubber design
Rick, would that matter? It seems it would just be based on the amount
of CO2 being generated via respiration. It might influence the way you
set up the circulation system. Correct?
JT
In a message dated 3/13/2011 3:30:33 P.M. Central Daylight Time,
landnsea1@hawaiiantel.net writes:
Cliff,
I noticed in your post below that you mentioned "30 lbs of Sodasorb =
80 hours of life support for one man" What internal volume are you basing
that on?
Rick
From: JimToddPsub@aol.com
Sent: Sunday, March 13, 2011 10:13 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] open source scrubber design
Cliff,
1. My first thought was to split the total amount of Sodasorb into two
identical canisters, but then it occurred it might cut operating costs to
have one smaller canister adequate for most missions and a second larger
canister (sealed) plumbed in for longer missions and long term life
support. That way you're not having to dump as much unused Sodasorb.
2. In sizing canisters for one and two person subs, is there some
relatively constant ratio between diameter and length, or should the
variability just be in the length of the canisters (constant diameter)
when designing for various capacities?
3. What size canister(s) are you contemplating for your next design?
I like the complete redundancy Alan referenced on the DW2000, but
accessible space can get short in a hurry in very small subs. Thanks for
your comments.
Jim
In a message dated 3/13/2011 1:40:12 P.M. Central Daylight Time,
cliffordredus@sbcglobal.net writes:
Emile
When I build my boat, I to did some investigation into commercially
available scrubber systems that would be applicable for a one man psub.
I did not find any that were economically viable. While I agree with
Leander that fundamentally the scrubber is not complicated, to make an
efficient and practical scrubber takes some work. I went through several
iterations on mine. One of the key items is, as you mention, the fan.
ABS requires 72 hours of emergency life support after your primary
mission time and this has to be able to run off the emergency battery
bank. If you under size the fan to minimize the power requirement to the
fan, then the fan can not generate sufficient differential pressure
across the fan to circulate the contaminated air. This is particularly
true if you use an axial flow fan rather than a radial centrifugal fan.
Axial fans are commonly installed on most PC computers. They are
designed for high flow rate but low head. I made the mistake of using an
axial flow fan on my first iteration of my scrubber. While it would last
80 hours ( the current load is very small), the scrubber effectiveness
was not great probably because the blades very stalling. My initial CO2
level would start at about 350 ppm but would build to 5000 ppm (0.5 mole
%) over 30 minutes. My second iteration replaced the axial fan with a
small radial centrifugal fan (squirrel cage) which developed four times
the head at about 1/4 of the flow rate. The current demand was only
slightly higher. This worked great while still meeting the low current
requirment.
The scrubber absorbent choice to me is a no brainier. Sodasorb HP is
what is used most often these days for psubs and re-breathers for divers.
It is easy to get and not very expensive. From a design perspective,
after sorting out the fan, it comes down to how do want to handle the
storage of the emergency Sodasorb. There are three options, 1)
cartridges for the primary and emergency absorbent, 2) scrubber sized to
hold the primary and emergency absorbent 3) scrubber sized for the
primary absorbent and spare Sodasorb stored in bulk requiring refill when
primary absorbent becomes saturated. There are advantages and
disadvantages to each technique. While cartridges are easy to replace
in an emergency situation, the spare cartridges don't pack as efficiently
as bulk absorbent. For a small psub like mine, this rules them out; I
just did not have the room. I note that the Deepworker uses the option
2) . For small one man psubs, I think option 2 is probably the best way
to go. The disadvantage to this approach is that for non emergency
conditions, you end of tossing a lot of partially used Sodasorb after
each dive. For a one person sub, this is not an issue but for more than
one, this makes this option not as attractive. Also, because it is
inexpensive, this is not a big deal for a one person sub. This option
provides the least stress in a stressful emergency as the operator does
not have to worry about changing out the absorbent when it becomes
saturated. On my boat, I use option 3 primarily because of the storage
issue. On my next one person boat, I would go with option 2. Replacing
30 lbs of Sodasorb (80 hours of life support for one man) is not a big
deal given that it simplifies life.
While the manufactures of these absorbents add a chemical that turns
the absorbent a different color than white when it becomes saturated,
this is not very practical to use as lighting in subs make it hard to
detect the color change. A better detection of a saturated absorbent is
a good CO2 sensor with an audible alarm.
So to me, it comes down to correctly specifying the fan and how to
package the spare absorbent.
Cliff
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