Re: [PSUBS-MAILIST] Humidity control

Jon, I concur, I am not sure how low a dry air purge would drop the RH in my boat. It would be easy to test in my shop. I have used shop air to purge my boat to drop the CO2 level back to normal air levels but my shop air is not dry. A scuba tank would work.

I saw a comment in the "Design guidelines for Carbon Dioxide Scurubbers" by Nuckkas et.al., (ncsc TECHMAN 4110-1-83) that said "As a general rule, moisture levels of the incoming gas stream should be maintained above 70 percent RH when using SodaSorb or Baralyme." They site a reference a US Navy report. I am not sure how hard and fast this is or how much degradation of the scrubber occurs at lower RH's.

Cliff Redus
Redus Engineering
USA Office: 830-663-6445
USA mobile: 830-931-1280
cliffordredus@sbcglobal.com

From: Jon Wallace <jonw@psubs.org>
To: personal_submersibles@psubs.org
Sent: Thu, March 17, 2011 12:36:24 AM
Subject: Re: [PSUBS-MAILIST] Humidity control

In a larger cabin such as the K-boats the air purge shouldn't be as much of an issue due to the larger volume of air. It's also not clear whether such a purge would be efficient enough to bring the RH to near-zero even in a cabin as small as the R-300. Assuming it did bring RH down to 20% or so, the question becomes more about how much water vapor sodasorb (or similar product) requires to activate CO2 capture. I don't know if that data is available from any product specifications.

Jon

On 3/16/2011 3:38 PM, Cliff Redus wrote:

Sean, I also think this is true also. I have a relative humidly sensor in my boat. When I did an 8 hour test in my boat in which I do not have any RH control, at the time the hatch was closed, the RH was 50%. After about one hour, the RH climbed to around 80%. Over the next 3 hours, the RH climbed to 85% and stayed at this level for the duration of the test. This leads me to believe that the primary source of condensed water vapor in the boat is due to exhalation of 100% RH air. I think that purging the pressure hull with dry air prior to hatch closing would bring down the initial RH to near zero but quickly for a small psubs like mine, it would climb rapidly. As the chemical reaction in the scrubber needs water vapor to work, this concept would seem to me to be counter effective to scrubber operations.

In the spirit of KISS, I am not sure it makes sense to try and condition the air to regulate RH anyway.

Cliff