Mass Flow

robertfondren · 15th November 2006, 08:20

Would a mass flow regulator set to deliver 100% o2 at .8lpm deliver the same number of molecules of oxygen as a MFR set to deliver 40% 02 @ 2lpm?

**bathtub** · 15th November 2006, 13:35

be a bit careful as we are mixing mass and volume. but essentially yes.

paulraymaekers · 15th November 2006, 15:04

Quote: (Originally Posted by robertfondren)

Would a mass flow regulator set to deliver 100% o2 at .8lpm deliver the same number of molecules of oxygen as a MFR set to deliver 40% 02 @ 2lpm?

yes, but if you do that in a CMF type closed breather, your PPO2 wil sink like a bric in the water!

(you simply transform your mCCR into a SCR with the EAN40 flow at 2l/min)

paul

robertfondren · 16th November 2006, 05:44

Thanks, one and all!

robertfondren · 16th November 2006, 05:55

Why would the patial pressure of 02 drop like a brick if one were receiving the same number of molecules of 02 per minute ?

I suspect I'm missing something.

decoweenie · 16th November 2006, 06:39

Quote: (Originally Posted by robertfondren)

Why would the patial pressure of 02 drop like a brick if one were receiving the same number of molecules of 02 per minute ?

I suspect I'm missing something.

You are adding 40% O2 and 60% diluent at the same time.

jaap · 16th November 2006, 07:01

Quote: (Originally Posted by robertfondren)

Why would the patial pressure of 02 drop like a brick if one were receiving the same number of molecules of 02 per minute ?

I suspect I'm missing something.

OK so lets look at the simple case:

If you use a flow of 0.8 l/min of 100% O2 (no other gas is introduced) you either get enough O2 or you don't. That is if you metabolise less than 0.8 l/min you will accumulate O2 in the loop and eventually have to dump some.

If you metabolise more than 0.8l/min you will not have enough O2. If you only have 100% O2 in the loop (in theory) then you will notice this since you eventually will not have enough O2 in there to breath.

OK?

But if you run 40% O2 at 2 lmp the case is very different. Since you now introduce a gas with 60% inert gas and your body is only using the O2 you will accumulate gas rather rapidly in the loop, This gas will have to be dumped. Since there are no magic dumpvalves that only dump inert gas keeping the O2 in the loop you will dump gas containing O2. So you will loose O2 out of the loop.

Unless you have an extremely low O2-consumption (very unlikely) you will not get enough O2 from such a low flow of 40% O2. The very dangerous part of this is that since you now have a flow that is also introducing a lot of inert gas you will not get any warning by not being able to breath.

So if you attempt to survive on a 2 lmp flow of 40% O2 you will most likely go unconscious very fast. That is unless you have some working O2-monitoring and take the right actions.

In order to understand the maths behind it take a look at this page:

Åkes’ Constant Massflow Rebreather Technical Page

paulraymaekers · 16th November 2006, 07:20

Quote: (Originally Posted by robertfondren)

Why would the patial pressure of 02 drop like a brick if one were receiving the same number of molecules of 02 per minute ?

I suspect I'm missing something.

or to put it very simple:

each minute you inject 0.8l ox and 1.2 l pure nitrogen
each minute your body consumes 0.8l ox, means you take out 0.8 l ox out of your breathing lung

so in total(netto): each minute you inject 1.2l pure nitrogen in your breathing lung: you dillute your breathing mix constantly with pure nitrogen... nothing much for breathing at the end :-)

paul

15th November 2006, 08:20	#1 (permalink)
robertfondren New Member Current Rebreather/s: Ray Other Rebreather/s: Not Bought Yet Ray Join Date: Mar 2006 Location: u.s.a. Posts: 79	Mass Flow Would a mass flow regulator set to deliver 100% o2 at .8lpm deliver the same number of molecules of oxygen as a MFR set to deliver 40% 02 @ 2lpm?
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15th November 2006, 13:35	#2 (permalink)
bathtub What bubbles? - DOH ! Current Rebreather/s: Dolphin Other Rebreather/s: Dolphin Join Date: Oct 2006 Location: Switzerland, Zug Posts: 35	Re: Mass Flow be a bit careful as we are mixing mass and volume. but essentially yes.
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15th November 2006, 15:04	#3 (permalink)
paulraymaekers rEvo's daddy Current Rebreather/s: rEvo Other CCR Home Build Other Rebreather/s: rEvo Other CCR Home Build Join Date: May 2005 Location: belgium Posts: 1,494	Re: Mass Flow Quote: (Originally Posted by robertfondren) Would a mass flow regulator set to deliver 100% o2 at .8lpm deliver the same number of molecules of oxygen as a MFR set to deliver 40% 02 @ 2lpm? yes, but if you do that in a CMF type closed breather, your PPO2 wil sink like a bric in the water! (you simply transform your mCCR into a SCR with the EAN40 flow at 2l/min) paul __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...
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16th November 2006, 05:44	#4 (permalink)
robertfondren New Member Current Rebreather/s: Ray Other Rebreather/s: Not Bought Yet Ray Join Date: Mar 2006 Location: u.s.a. Posts: 79	Re: Mass Flow Thanks, one and all!
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16th November 2006, 05:55	#5 (permalink)
robertfondren New Member Current Rebreather/s: Ray Other Rebreather/s: Not Bought Yet Ray Join Date: Mar 2006 Location: u.s.a. Posts: 79	Re: Mass Flow Why would the patial pressure of 02 drop like a brick if one were receiving the same number of molecules of 02 per minute ? I suspect I'm missing something.
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16th November 2006, 06:39	#6 (permalink)
decoweenie Crash Test Dummy Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Feb 2005 Location: Cairo Posts: 5,487	Re: Mass Flow Quote: (Originally Posted by robertfondren) Why would the patial pressure of 02 drop like a brick if one were receiving the same number of molecules of 02 per minute ? I suspect I'm missing something. You are adding 40% O2 and 60% diluent at the same time. __________________ "...after a while you get bored offering advice to a bull that like to keep butting the fence with its head rather than walking through the open gate..." - Rebreather World PM
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16th November 2006, 07:01	#7 (permalink)
jaap Normal people worry me Current Rebreather/s: Classic Kiss Other CCR RB80 / Clone Ray Other SCR Home Build Other Rebreather/s: Other CCR RB80 / Clone Ray Other SCR Home Build Join Date: Jun 2005 Location: Stockholm Sweden Posts: 451	Re: Mass Flow Quote: (Originally Posted by robertfondren) Why would the patial pressure of 02 drop like a brick if one were receiving the same number of molecules of 02 per minute ? I suspect I'm missing something. OK so lets look at the simple case: If you use a flow of 0.8 l/min of 100% O2 (no other gas is introduced) you either get enough O2 or you don't. That is if you metabolise less than 0.8 l/min you will accumulate O2 in the loop and eventually have to dump some. If you metabolise more than 0.8l/min you will not have enough O2. If you only have 100% O2 in the loop (in theory) then you will notice this since you eventually will not have enough O2 in there to breath. OK? But if you run 40% O2 at 2 lmp the case is very different. Since you now introduce a gas with 60% inert gas and your body is only using the O2 you will accumulate gas rather rapidly in the loop, This gas will have to be dumped. Since there are no magic dumpvalves that only dump inert gas keeping the O2 in the loop you will dump gas containing O2. So you will loose O2 out of the loop. Unless you have an extremely low O2-consumption (very unlikely) you will not get enough O2 from such a low flow of 40% O2. The very dangerous part of this is that since you now have a flow that is also introducing a lot of inert gas you will not get any warning by not being able to breath. So if you attempt to survive on a 2 lmp flow of 40% O2 you will most likely go unconscious very fast. That is unless you have some working O2-monitoring and take the right actions. In order to understand the maths behind it take a look at this page: Åkes’ Constant Massflow Rebreather Technical Page __________________ My initials: JAAP
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16th November 2006, 07:20	#8 (permalink)
paulraymaekers rEvo's daddy Current Rebreather/s: rEvo Other CCR Home Build Other Rebreather/s: rEvo Other CCR Home Build Join Date: May 2005 Location: belgium Posts: 1,494	Re: Mass Flow Quote: (Originally Posted by robertfondren) Why would the patial pressure of 02 drop like a brick if one were receiving the same number of molecules of 02 per minute ? I suspect I'm missing something. or to put it very simple: each minute you inject 0.8l ox and 1.2 l pure nitrogen each minute your body consumes 0.8l ox, means you take out 0.8 l ox out of your breathing lung so in total(netto): each minute you inject 1.2l pure nitrogen in your breathing lung: you dillute your breathing mix constantly with pure nitrogen... nothing much for breathing at the end :-) paul __________________ www.rEvo-rebreathers.com .... the earth is flat, Elvis is alive, and radial scrubbers give longer dwell time than axials...
(Online)

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