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Thread: An An attempt to clear the misconception on CMF

  1. #11
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    Re: An An attempt to clear the misconception on CMF

    Non Sealed Regulator IP 3 barg.jpg

    In the above example all other parameters (orifice size, temperature, compressibility factor, etc etc) are the same except the IP.

    The flow will never stop if you are using a non-sealed regulator. This is not a paradox. Perhaps the misleading issue is the fact that the flow velocity will become slower and slower as you are descending below the sub-sonic zone but it will never stop. The gas will be denser, hence the mass flow will continue to increase. That's physics. No very straight forward but should one goes into the formulas which are widely available in textbooks, then one will produce more or the less the same results.
    Last edited by diveoceanos; 6th January 2010 at 19:59.

  2. #12
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    Re: An An attempt to clear the misconception on CMF

    Hi Sotos, thanks for the explanation, can you share the formula as well.
    And good work!

    Quote Originally Posted by diveoceanos  View Original Post
    Hi Jonny.

    The function it is not linear in the second example but appears to be one. I will try to upload an other graph where the IP is lower and the curving will be obvious.

    We are using a small diameter orifice in both cases.

    The curves are derived by an excel file where we have as input all the parameters and a widely known formula for sonic and subsonic flow is being used.
    Last edited by Johnny Bekkestad; 6th January 2010 at 19:58.

  3. #13
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    Re: An An attempt to clear the misconception on CMF

    I can share the excel file with the formula in it. Send me a PM to arrange for that.

    Thanks.

  4. #14
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    Re: An An attempt to clear the misconception on CMF

    equations cmf.pdf

    Also a pdf file with the formulas I used (the file does have formulas for not only gases).

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    Re: An An attempt to clear the misconception on CMF

    Quote Originally Posted by diveoceanos  View Original Post
    Attachment 17574

    Also a pdf file with the formulas I used (the file does have formulas for not only gases).
    Sotos,

    i want to know what was your grade in Maths at school mate? only asking because if it was anything less than A+ then i wont blame you if the dude if found 200m with a weight belt around his neck...

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    Re: An An attempt to clear the misconception on CMF

    Nice work, Sotos!

    Have some green...

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    Re: An An attempt to clear the misconception on CMF

    Quote Originally Posted by diveoceanos  View Original Post
    Attachment 17574

    Also a pdf file with the formulas I used (the file does have formulas for not only gases).
    Reminds me of my old power engineering exams, well done.

  8. #18
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    Re: An An attempt to clear the misconception on CMF

    Fantastic Sotos!
    Great job, very well done.
    Thank you for posting.
    manthos
    Manthos Marras

  9. #19
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    Re: An An attempt to clear the misconception on CMF

    Are you sure that the formula for the sonic orifice is applicable to the flow regulator of Azimuth or Voyager?
    RG

  10. #20
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    Re: An An attempt to clear the misconception on CMF

    Quote Originally Posted by trimix63  View Original Post
    Are you sure that the formula for the sonic orifice is applicable to the flow regulator of Azimuth or Voyager?
    RG
    Quote Originally Posted by trimix63  View Original Post
    Are you sure that the formula for the sonic orifice is applicable to the flow regulator of Azimuth or Voyager?
    RG

    Why not? However, I am open to suggestions if you have a different opinion or data to prove that this is not the case. I can always be wrong mate. Who am I after all?

    I am just making a use of gas flow physics in an effort to explain the real world. As a matter of fact other people in this forum did some experiments to show that the flow with depth compensating regulators is not the same and it is dependent on the IP eventhough the flow speed is the same and remains at sonic level. I have also seen in an other post a fellow diver reporting that in a very deep dive the diver needed to add diluent in his Voyager loop to keep O2 down. I have seen other people claiming that the mass flow is the same no matter what the depth is.

    I don't know the details of Voyager or Azimuth valves. What is special with them apart from being needle valves? Is there a sort of compensating mechanism which is automatic and when the gas density goes up (increased IP with depth) the velocity goes down to offset this?

    To kick it a bit further; thinking of the consequences that such an information might have on dive planning I can immagine that worng information can kill. How? Lets suppose that I am correct. But you have been tought that mass flow with your rebreather is constant and not dependent on the depth. You set your surface flow to 0,7 LPM CCR. Then you are relaxed down to 45 meters and taking photographs your mass flow goes to 1,1 - 1,2 LPM. 10 minutes at this depth and you are "so relaxed" that you don't even make a check in your PPO2. Suddenly you check! Your monitors show let's say 1,9. And you get stressed! Reaction? Aggressive diluent flush and recheck if you act appropriately. Or panic, attempt to bail out, lost of bouyancy, uncontrolled ascent and bla bla bla...and there you go! Not to mention bailing out to the wrong mix under the influence of psychological stress.

    In either case what is probably one good consensus is that PPO2 need to be monitored in a continous basis. But would you be interested to know it if Mass Flow with depth compensating (variable IP) regulators is not constant?

    My opinion is written above, but that is just an opinion. Errors and Ommisions accepted!
    Last edited by diveoceanos; 12th February 2010 at 17:25.

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