<div dir="ltr"><div><font color="#000000" face="Times New Roman" size="3">
</font><p style="margin:0in 0in 10pt"><font face="Calibri"><font size="3"><font color="#000000">To elaborate a bit on Alec's comments, a few years back I did some work the scrubber for my one-man
boat and came away with some conclusions.<span>
</span></font></font><font color="#000000" size="3">The first was that a radial design was better than an axial design for
air flow throws the absorbent and the second was that the goldilocks rule applies
for fan/blower associated with the scrubber.</font><span><font color="#000000" size="3">
</font></span><font color="#000000" size="3">Engineers make a distinction on equipment used to compress air.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">They define a parameter known as the specific
ratio which is defined as the discharge pressure divided by the supply pressure
where each pressure is in terms of absolute pressure rather than gage
pressure.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">If the device has a specific
ratio less than 1.1, they call it fan, if it has a specific ratio greater than
1.2 they call it compressor and if it has a specific ration between 1.11 and
1.2, it is a blower.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">What I found from my
testing on the scrubber was that fans like you would typically see on PC are
axial flow and these are designed for high flow rates but low head. When you
try and use them to push air through the CO2 absorbent, they just don't have
enough head and the resulting flowrate is very low.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">In this case they are not operating anywhere
near their best efficiency point (BEP).</font><span><font color="#000000" size="3">
</font></span><font color="#000000" size="3">What I found worked better were squirrel cage blowers. These are
designed for lower flow rates than PC axial fans but with more head.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">I am sure there are many models of squirrel
blade blowers that would work but the model I use is from Papst, model
RL90-18/24.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">This blower operates off
24VDC and has a power rating of 7.5 W which translates to 0.31 amps.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">If you look on ebay, these blowers come up
all the time.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">Back to the goldilocks
rule;</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">to meet ABS rules, you have to demonstrate
that your life support system will operate through the the emergency time
period which is 72 hours on the backup battery.</font><span><font color="#000000" size="3">
</font></span><font color="#000000" size="3">The current during this period is known as the “Hotel Load” for obvious
reasons.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">When I tested axial PC fans,
they were great on battery endurance because they pull a very low current but
they did not work well because they did not have enough head to overcome the
pressure drop through the CO2 absorbent material , SodaSorb HP in my case.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">This showed up as having erratic CO2 levels
in the boat and not being able to sustain concentrations less than ABS required
maximum of 5000 ppm (1/2%).</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">When I tried
larger axial fans like you would use for a bilge fan, the unit would keep the
CO2 level below the 5000 ppm limit but they pulled way much current and </font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">would not last anywhere near the 80 hours.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">The Papst, model RL90-18/24 squirrel cage
blower turned out to be </font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">perfect with
enough head to circulated</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">the cabin
air</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">to keep the CO2 level typically
below 2000 ppm but also because they only pull 0.31 amps.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">This blower did not let me meet the 72 ABS
endurance limit but got me close.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">Below
is a graph of hotel load current through my backup battery and the voltage
across the backup battery as a function of time on a life support test in my
boat.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">You can see from the graph at
about 69 hours into the test the backup battery was exhausted.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">Also the hotel load started at about 1.6 amps
but slowly climbed to 1.7 amps over the 69 hours.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">This hotel load was a little higher than the
1.5 amps that I had designed around.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">I
need to go back and look at the contributors to this hotel load and see if I
can reduce.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">I am happy with the 69 hours
because during a real emergency like be stranded on the bottom due to entanglement,
I could utilize at least some of the main battery.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">For reference, the backup battery consist of
two AGM</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">100 Ah battery.</font><span><font color="#000000" size="3"> </font></span><font color="#000000" size="3">If you divide the capacity by the hotel load
you get the expected endurance of 100Ahr/1.65A is 61 hours so my 69 hours did better
than expected.</font><span><font color="#000000" size="3"> </font></span></font></p><font color="#000000" face="Times New Roman" size="3">
.</font></div><div><br></div><div><img width="561" height="370" alt="Inline image 2" src="cid:ii_15b9b08028ff8452"></div><div><br></div><div><br></div><div>Cliff </div><div><br></div><div><br></div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sat, Apr 22, 2017 at 6:07 PM, Alec Smyth via Personal_Submersibles <span dir="ltr"><<a href="mailto:personal_submersibles@psubs.org" target="_blank">personal_submersibles@psubs.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hi Brian,<div><br></div><div>If by "straight flow fan" you mean the geometry you would see on a computer cooling fan for instance, they are way less efficient for this purpose. I believe the reason is they move good volumes of air but develop very little pressure. I've tested both kinds, and the sort I'm using now has much better performance. Cliff has done similar tests and had the same results.<div><br></div><div>Best,</div><div><br>Alec</div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sat, Apr 22, 2017 at 6:08 PM, Brian Hughes via Personal_Submersibles <span dir="ltr"><<a href="mailto:personal_submersibles@psubs.org" target="_blank">personal_submersibles@psubs.<wbr>org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid">
<div>
<p style="text-align:left;color:black;font-family:sans-serif;font-size:11pt;margin-top:25px;margin-bottom:25px;background-color:white" dir="auto">
Alec,</p>
<p style="text-align:left;color:black;font-family:sans-serif;font-size:11pt;margin-top:25px;margin-bottom:25px;background-color:white" dir="auto">
Just ordered a tank holder that has two bungies about an inch apart, used to strap tanks down on a boat. I'm thinking I can hang this scrubber from the roof using the aft most reinforcing ring, holding it up in the middle. If it works, straight flow fan.<br>
</p>
</div>
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