RE: [PSUBS-MAILIST] Scrubber CFM

["Greg" <greg@precisionplastics.com>]

Hi Jon,

The only way to know the true airflow over the surface is to measure the
flow entering or exiting the unit. The true CFM is not only a function of
the fan rating but also restrictions to flow in a particular scrubber design
and type of fan used (radial/axial). 

Where a flow meter when you need one?!


Greg C


-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Jon Wallace
Sent: Thursday, August 11, 2011 11:40 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Scrubber CFM


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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