[PSUBS-MAILIST] co2 scrubber

Mon Feb 13 02:30:29 EST 2017

Sean,
in this email you are advising keeping humidity between 30 & 70%.
Any ideas on the best way of doing that? I am going to use a humidity
sensor & PLC, so have the option of automating functions.
   Have thought of having some sought of valve that channels air through
a filter prior to the scrubber, when humidity is high. 
Another thought was blowing air under a raised floor so that moisture
laden air was forced between the floor & hull, & condensed against the
cold hull.  I have thought about peltier coolers also, as they have the dual
option of being heaters by reversing the current. They are a bit expensive
on power though.
Alan

Sent from my iPad

> On 5/02/2017, at 2:31 PM, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> I am skeptical of the utility of the colour indicating absorbent. The reaction front in an axial scrubber is unlikely to be planar (unless perfectly diffused), but rather conical, so you could have breakthrough in the center before the indicating edge approaches the end of the canister, for example. I think actually measuring the CO2 accurately and using the rise in level as the indicator of scrubber breakthrough is the better course of action. One thing to note is that the colour change in the indicating absorbent is usually subtle, and submarine interiors are usually subdued light environments. In some media, the colour is readily apparent immediately after reaction, but the colour fades when left to stand for some time.  Also, even if you have an acrylic or polycarbonate canister, dust from the scrubber media can accumulate on the inner wall and make visual inspection difficult.
> 
> If I were me, I'd be inclined to design a scrubber that would permit relatively easy media or canister changes in situ, with a designed capacity equal to the mission time + reserve time (or split between multiple scrubbers), and then keep one or two additional sealed canisters or media changes tucked away on board.  That way, you can make effective use of the media by exhausting it right to breakthrough. If you make short dives, you can do several on the same canister, and if you reach breakthrough (arbitrarily set but below the permissible limit), you change it out. I would choose a radial flow design, with airflow from outside to inside for maximum efficiency, and consider addressing the operating humidity of the sub to keep it between 30% and 70% RH.  Some moisture is actually required for the scrubber to function, as the chemical reaction actually occurs in aqueous solution on the surface of the media granules. I would definitely make a point of ke! eping a partially used scrubber sealed off from atmospheric air when not in use. In the absence of a sealed container, simply keeping your hatch closed would suffice, as once the CO2 in the cabin is all reacted it is inert. Atmospheric air has 400 ppm CO2 in it, which will consume a scrubber over time if left exposed.
> 
> Sean
> 
> 
>> On February 4, 2017 5:45:26 PM MST, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>> I'd like to do a radial scrubber design but I also would like to use the indicating SodaSorb, so I can see the color change.  Being able to see the color change with a radial design would be a challenge !
>>  
>> Brian
>> 
>> --- personal_submersibles at psubs.org wrote:
>> 
>> From: "Sean T. Stevenson via Personal_Submersibles" <personal_submersibles at psubs.org>
>> To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
>> Subject: Re: [PSUBS-MAILIST] co2 scrubber
>> Date: Sat, 04 Feb 2017 14:53:27 -0700
>> 
>> Yes. For the chemical reaction to work properly, the air needs some dwell time against the scrubber media. This may be specified in the media datasheets. Regardless, if your fan is too strong and you're blowing tons of air through it, you may just dry it out while scrubbing really inefficiently.  If you! slow it down, you give the CO2 time to react and the bed gets more efficient. This is one of the reasons why radial flow scrubbers have an advantage - the surface area is huge, so the actual flow velocity through the bed is minimal in comparison to an axial flow design. You only need enough airflow to remove CO2 faster than you produce it, and ideally to process the entire air volume in your cabin a few times an hour. Slow, large diameter fans will be more effective than a high speed but small fan, and probably easier on your batteries too.
>> 
>> Sean 
>> 
>> 
>> On February 4, 2017 2:38:32 PM MST, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>> Is there such a thing as to TOO much air flow through a scrubber ??
>>  
>>  
>> Brian
>> 
>> --- personal_submersibles at psubs.org wrote:
>> 
>> From: Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org>
>> To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
>> Subject: Re: [PSUBS-MAILIST] co2 scrubber
>> Date: Fri, 3 Feb 2017 09:34:40 -0600
>> 
>> Brian, see http://www.ntz-filter.com/Radial_Filtration_versus_Axial_Filtration for picture which is worth at least a hundred words.
>> 
>> Cliff
>> 
>> 
>> 
>> On Thu, Feb 2, 2017 at 11:36 PM, Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>> What is the difference between a Axial scrubber and a radial ?
>>  
>> Brian
>> 
>> --- personal_submersibles at psubs.org wrote:
>> 
>> From: via Personal_Submersibles <personal_submersibles at psubs.org>
>> To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
>> Subject: Re: [PSUBS-MAILIST] co2 scrubber
>> Date: Thu, 2 Feb 2017 16:29:34 -0600
>> 
>> Started life with axial scrubber but now use radial design.  Has ! worked much better for me.
>> 
>> Cliff
>> 
>> Sent from my iPad
>> 
>> On Feb 2, 2017, at 1:06 PM, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>> 
>> Thanks' guys, that helps.  
>> Cliff, I assume you have an axial scrubber
>> Hank
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