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Jon,
I searched a bit trying to find the operational and efficiency curves
of Sodasorb over a range of RH, but didn't locate anything useful. It
would probably be easiest to ask the producer. However I'd better tear
myself away and get to doing the things here I really must do which have
nothing to do with subs.
Hopefully several of our members with operational vessels will have an
opportunity to record lots of data. I'll add an exterior water temp probe
to my instrument list. Eventually I'd like to get an automatic data
recording system, but first I just want to get the design finished and in the
water.
Jim
In a message dated 3/16/2011 8:40:56 P.M. Central Daylight Time,
jonw@psubs.org writes:
Jim,
It's possible, but I suspect that depends more upon
the cabin volume than anything else. Given the data from Cliff's test,
the RH increased at a rate of .4% per minute and his CO2 increased at a rate
of 54ppm per minute. He topped out a 4300ppm (after approximately 75
minutes) which is close to the 5000ppm maximum recommended and would have
required a functioning scrubber. In the same time period, the RH rose
30%. Assuming worst case and a cabin air purge that brought the RH to
0%, the scrubber would have to work effectively with an RH of about
30%.
A water test is going to be much different, not only because the
cabin air temp will reach equilibrium with the air temp, but the water will
draw heat from the sub faster than air. However, using Cliff's data as
an example, he started off with 60% humidity in the cabin and within about 30
minutes the cabin had reached a dewpoint of about 70F which matched the
outside temperature and condensation could have started forming if the inside
of the acrylic dome was at the outside temperature. Cliff probably did
not see condensation at this point because of his body heat affecting the dome
and the relatively inefficient air-to-air transfer of heat through the
acrylic.
Theoretically at least, had Cliff purged the cabin and gotten
the RH down to 30% it would have provided another 75 minutes of time before
the dew point matched the outside temperature of 70F, providing a total of 105
minutes of condensation free "dive time" as opposed to the 30 minutes when he
started at 60% humidity. Notwithstanding scrubber RH requirements, it
would seem purging cabin air with dry scuba air might have some value for
"short dives", even in a small sub.
It's possible that such air purging
is so inefficient a process that it doesn't even dramatically reduce the RH in
the cabin. So I don't know...it's just an idea I found
interesting. When I get going on my own sub I'll try it out and report
back with the results.
Jon
On 3/16/2011 7:57 PM, JimToddPsub@aol.com wrote:
Jon,
I wonder how much that matters. The CO2 level is going to be very
low when you first seal in. RH will be rising simultaneously with the
rise in CO2. If you're starting with an RH of 20%, it should get into
the operational range of the scrubber fairly quickly.
I think one of Sean's emails might have referenced the RH operating
range for scrubbers; I'll search later.
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