Alan,Here's a photo of the DW2000 scrubbers. http://www.psubs.org/convention/2009/photos/pics.cgi?jonw/DSCN0778.JPG
A 160 liters/minute airflow is pretty low velocity. Your typical 80mm computer fan is pushing about 840 liters/minute. I can tell you from personal experience that the airflow coming out of the scrubber fans of the DW2000 is so low velocity that you have to put your hand as close as a few millimeters from the fan blades to feel it. While I was waiting for the crane to lift me into the water (with the hatch closed) one of the things I noticed was the lack of fan noise that I expected from the scrubbers, so I put my hand down to the fan and sure enough it was running but the air velocity was surprisingly minor. Also, while the fan might have been rated at 160 liters/minute in open air, the soda lime is going to cause friction on the air and slow it down as it travels through the scrubber (hence you get your dwell time).
There's only so far you can get with raw numbers when it comes to scrubbers. The variables involved in totality of the design require practical testing with either lab equipment that can measure air flow and chemical content, or in the finished sub (on land, NOT in the water) with an O2 and CO2 meter to see how it performs over time.
Also remember that the effective capacity of your scrubber is not going to be the volume of material you put in it, due to "chemical saturation" (slide 12 in my online slide set).
Jon Alan James wrote:
To All, While looking at various papers on CO2 scrubbers from manufacturers etc, I found that none addressed the unique situation found in submarines. Most CO2 absorbent is used in anesthetic machines or rebreathers wherethere is a closed circuit. The CO2 breathed out goes straight into the scrubber& is removed.In our subs the CO2 is breathed out & is diluted by the rest of the air in the hull & only air with a portion of the CO2 in the hull goes through the scrubber. This means that the CO2 level & the pressure in the hull will progressively climb unless the volume of air going through the scrubber is large enough to make an impact. The Deep Worker 2000 has fans pushing 160 liters per minute, I'm notsure whether this is per scrubber & whether they have 2 scrubbers workingsimultaneously. But based on 1 fan going, that's 320 x the volume of CO2 being produced. In the manufacturers guidelines for scrubbers they recommend that the flow is at least equal to the tidal volume of your breath (about 10 liters per minute) & low enough so that the air has at least 1/2 a second dwell time in the canister. This could be 32 x less than what Phil has worked out is necessary for the Deep Worker. I know the Deep Worker has a small hull & that fluctuations in O2 & CO2 are more critical than a K250, but possibly the same volume of flow isnecessary to achieve atmospheric control in larger subs.Also because of the dwell time needed the large flow required would need large orlong canisters. Deep Worker has 2x 3.35 kg scrubbers.On the psub site there is reference to rebreather cartridges as an option, but from what I've found you would probably need a number of these running simultaneouslyto make head way.What are ABS recommendations? & what are others thoughts / experiences with this.I'm trying to sort this stuff out for myself. Regards Alan
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