[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PSUBS-MAILIST] CO2 absorbant efficiency
Thanks Jon, Hugh & Phil,
Have now tracked down enough information to proceed with a scrubber
design. I have the sofnolime 797 grade wich according to the specs
absorbs 150 liters per kg. On the sodasorb site it gives 8hrs use per kg
at the 150 liter rate. This is just a little short of Phils figures for the
sodasorb high
performance grade, so I'll work on the 8hrs per kilo as being the most I can
expect.
Regards Alan
----- Original Message -----
From: "Jon Wallace" <jonw@psubs.org>
To: <personal_submersibles@psubs.org>
Sent: Thursday, June 10, 2010 2:46 PM
Subject: Re: [PSUBS-MAILIST] CO2 absorbant efficiency
Alan,
All my references are on the last slide of that presentation and I believe
I got my data point for capacity of the material at the Molecular Products
web site. The slide set presentation was written back in 2005 and the
specific page I referenced is no longer available but there are plenty of
other data sheets for various products on the molecular products web site.
There are different grades of soda lime which affect the CO2 capacity of
the product. By the looks of current data sheets on the molecular
products web site, it appears that I selected a rather low grade product
(100 liters/kg) since I can't find a product that has that low of a
capacity on their web site any longer (perhaps that's why they removed the
product??). It's possible that in the tests documented in phil's paper
they used a higher capacity product than the 100 liter/kg product I used
as a example, or the test subjects were better breathers than the numbers
I provided in my slide set, or maybe the product is actually more
efficient than molecular products is advertising.
Duration depends not only on CO2 capacity of the material but also on
efficiency of the scrubber, breathing rate, and tidal transfer of your
lungs. The breathing physiology numbers I used in my example probably
came from webmd.com (been too long, I can't recall) as referenced at the
end of the slide set, however practical testing with real numbers is going
to produce different results. So for example, if I change 20 breaths per
minute to 18, and change tidal transfer from .5 to .3, and use a product
with a capacity of 160 liters/kg from the molecular products web site, I
come up with 269 minutes duration per pound.
Both documents should be considered a reference for design but not taken
verbatim as consistent performance. When it comes to scrubbers "your
mileage may vary" is a very real statement just as mileage per tank of car
fuel depends upon the driver. I realize you are saying that the
difference between the two documents is large enough that it would
potentially impact design of storage capacity for extra scrubbing
chemicals. For early design purposes the safest bet would be to use the
more conservative approach if possible, or if that results in too large of
a physical space then you might split the difference. Worst case you end
up with more storage of chemicals which potentially translates to a longer
dive duration in event of emergency. I would also recommend that you
first determine exactly which brand and grade of soda lime you can readily
get access to and then secure a data sheet for it. For a theoretical
analysis you can follow the procedure in my slide set to get an idea of
duration based upon the published CO2 capacity of the chemical you intend
to use. However, realize that those numbers represent 100% efficiency (as
my slide notes) which you are unlikely to achieve. The most important
thing to do, is run a REAL practical test with your O2 and CO2 system in
the actual submarine before diving with it. Cliff Redus has photos on the
web site of him carrying out this kind of test. Then you will have a much
better idea of the performance of your life support and how much spare
chemical you need to bring with you for a specific duration period.
In regards to NASA and CO2 levels, Phil wrote his paper in 1998 while my
slides were written in 2005. NASA likely changed their dependencies and
requirements in that time period. My reference for that was "Spacecraft
Maximum Allowable Concentrations Volume 2, chapter B3" as shown at the
bottom of the slide set.
Hope that helps.
Jon
Alan James wrote:
Jon
Am designing my scrubbers & have come up with a discrepancy between
papers on the psub life support page.
Phils paper on life support states on page 6 that you get 4 hours (240
minutes)
per pound of soda lime.
Your scrubber design page puts it at 200 minutes per kg wich is 90
minutes
per pound (sofnalime). In other words Phils scrubber lasts about 2&1/2
times longer.
This is quite a differance if you are considering taking down enough
absorbant for 3 days.
Also ( nit picking now ) Phils paper states Nasa aborts missions at 3%
CO2 levels, while yours states 2%.
Regards Alan
************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003. Your email address appears in our database
because either you, or someone you know, requested you receive messages
from our organization.
If you want to be removed from this mailing list simply click on the
link below or send a blank email message to:
removeme-personal_submersibles@psubs.org
Removal of your email address from this mailing list occurs by an
automated process and should be complete within five minutes of
our server receiving your request.
PSUBS.ORG
PO Box 53
Weare, NH 03281
603-529-1100
************************************************************************
************************************************************************
************************************************************************
************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003. Your email address appears in our database
because either you, or someone you know, requested you receive messages
from our organization.
If you want to be removed from this mailing list simply click on the
link below or send a blank email message to:
removeme-personal_submersibles@psubs.org
Removal of your email address from this mailing list occurs by an
automated process and should be complete within five minutes of
our server receiving your request.
PSUBS.ORG
PO Box 53
Weare, NH 03281
603-529-1100
************************************************************************
************************************************************************
************************************************************************