|
I agree, Rick, didn't mean to put it THAT low. I'll also need to make
sure it's designed so water isn't sucked into the fan from the line.
On the other hand I might just scrap the whole concept and start over in
deference to better designs produced by others. It wouldn't be the first
time.
I plan to have all electrical components well protected from
splashes and water intrusion. To the extent practical I'd like to have
some of them completely water proof. If I can make the main instrument
module completely sealed, I can disconnect the wiring harness and remove it from
the sub entirely. In the same manner I plan to have sealed circuit breaker
boxes (2) that I can unplug from a harness and remove.
Cheers,
Jim
In a message dated 3/15/2011 12:26:59 P.M. Central Daylight Time,
landnsea1@hawaiiantel.net writes:
Jim,
The first thing that comes to mind on having
the fan low or anything else electric is damage from a wave entering either
from a boat wake in lake diving or wave in ocean diving like which is all I
will be doing. I plan on having most all my electric boards and connections on
the top and behind me for that reason.
Rick
Sent: Tuesday, March 15, 2011 4:29 AM
Subject: Re: [PSUBS-MAILIST] open source scrubber
design
Alec,
The comment about placing the fan near my feet was more about just
getting the noise away from my head especially if the acoustics of the canopy
turn out to be like a sound chamber. I'm expecting that the inlet for
the scrubber would be somewhere near my head. I like the concept of
having the fan downstream in the configuration to draw air through the
scrubber(s) instead of pushing it through. I also want to consider
electrical interference with other instruments and components in placing the
fan.
Since air exhaled during respiration contains moisture and the air
in a sub is often humid to begin with, I'm hoping there would be some
method of having the air as dry as possible prior to entering the scrubber,
but I have no specific concept or design in mind for accomplishing that
goal.
Depending on the temperature and moisture content of the air leaving the
scrubber system, it might be useful to duct it toward viewports to prevent
fogging.
I probably should drop out of discussions until after the April 15th tax
deadline, so if you don't hear from me for a bit, that's why. I'll catch
up later.
Cheers,
Jim
In a message dated 3/15/2011 8:42:29 A.M. Central Daylight Time,
Alec.Smyth@compuware.com writes:
From prior scrubber
experiments, the agent gets soggy and drips. There would be condensation on
the scrubber insides for sure. But water would still not run uphill, so if
the fan is mounted at the highest point I don't see a need for a water trap.
Your comment about putting the fan at your feet sounds like the fan might be
under the scrubber. Is that correct? In this present configuration, the
scrubber is a vertical cylinder (actually two concentric cylinders) with the
fan on top, drawing air through the center. The bottom end of the cylinder
can hold water.
BTW here's last
night's update. My new computer fans didn't arrive yesterday but I
poked around and found I had a squirrel cage fan on hand, just like the ones
Cliff had referred to only a bit bigger. Cliff's references were 75mm by
75mm. The one I had was 120mm by 120mm, 23 cfm, 50db. I adapted it to
the scrubber and tested with and without a Sofnolime load. BTW the
scrubber capacity turned out to be a hair under 10 lbs of
Sofnolime. I was very surprised by the result, compared to my earlier tests
with computer fans. Cliff, in a word you were right! Although I was not
measuring anything, seat-of-the-pants there is no noticeable decrease
in airflow when the scrubber is loaded. The fan didn't even notice the
resistance caused by drawing air through the Sofnolime, and was putting was
putting out a gale. Probably too much so, I can't imagine I would need quite
that much airflow. So last night I ordered a squirrel cage fan with about
half the airflow for another test. The 50db noise level
is tolerable but tiresome, and my goal is to find a fan that
has sufficient airflow yet no more than what is needed, in order to minimize
the noise.
To be
continued...
Alec
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
The contents of this e-mail are
intended for the named addressee only. It contains information that may be
confidential. Unless you are the named addressee or an authorized
designee, you may not copy or use it, or disclose it to anyone else. If
you received it in error please notify us immediately and then destroy
it.
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
************************************************************************
************************************************************************
************************************************************************
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
************************************************************************
************************************************************************
************************************************************************
|