Just another variable that needs to be considered as part of the testing process. Too large airflow and the air will be flowing too quickly for good CO2 transfer efficiency across the chemical. The fan I used to convert the ExtendAir canister may be way too big since the lowest setting is 20 cfm. Might be able to turn it down with a rheostat.
Jon On 8/11/2011 11:07 AM, Greg wrote:
I was talking with Tom Daley over at Micropore this morning about proper airflow through their "Extendair" cartridges (specifically the "SR0101C", which is a popular size used in a rebreathers) He did some quick calculations and came up with a value of 125 LPM (assuming 70 % efficiency of the cartridge)to meet the needs of the standard man at rest. I thought that this sounded surprisingly low- but Tom reminded me that calcium based scrubbers can easily dry out with too much airflow, specialty if the ambient humidity is low. I then referred back to Phil Nuytten's White paper and noted that he also specified a fan with a flow rate of only 160 LPM (page 5). 160 LPM translates to less than 6 CFM- a VERY small fan indeed. Most small CPU fans flow 30 CFM or more. Apparently Phil chose this size carefully (why am I not surprised?) Of course, the good news is that a 5 CFM fan also consumes very little power, which comes in handy in a long duration dive or emergency. Tom also suggested that a lung powered option might be best in an emergency, not only to save power but also because breathing into the canister supplies additional humidity. Of course, the optimum humidity range for Extendair cartridges may be different than the range needed using granules. Greg C
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