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Thread: V-Planner Nitrox mixing tools gives errors in results

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    V-Planner Nitrox mixing tools gives errors in results

    I have the Android v-Planner version and noticed the Nitrox mixer tools produces incorrect results. For example, starting pressure of zero, finish pressure of 3,000 with a 33 percent O2 says to add 423.4 psi of O2 and 2576.6 of air. However the correct O2 PSI of O2 to add is 455 PSI not 423 PSI.

    How do I know - I missed the question on my PADI Blender test.

    Ross, can you fix that, Please.

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    Re: V-Planner Nitrox mixing tools gives errors in results

    Didn't you see V-planners mixing tools use z-factors?

    Sent from my PAP4500DUO using Tapatalk 2

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    Re: V-Planner Nitrox mixing - z-factors

    Quote Originally Posted by jeffgerritsen  View Original Post
    I have the Android v-Planner version and noticed the Nitrox mixer tools produces incorrect results. For example, starting pressure of zero, finish pressure of 3,000 with a 33 percent O2 says to add 423.4 psi of O2 and 2576.6 of air. However the correct O2 PSI of O2 to add is 455 PSI not 423 PSI.

    How do I know - I missed the question on my PADI Blender test.

    Ross, can you fix that, Please.
    Your Padi tool probably uses Ideal gas mixing ratio's. The Mixer uses z-factors, which are one version of actual gas pressure properties (van der wals is another). You can find z-factors in the reference pages of a chemistry manual.
    Ross Hemingway
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    V-Planner PC, Mac, Mobile, iPhone-iPod, Android. MultiDeco Android, PC, Mac.
    V-Planner Live and MultiDeco-X1 for the Liquivision X1 dive computer.
    MultiDeco-DR5 for the DR-5 dive computer.

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    Re: V-Planner Nitrox mixing tools gives errors in results

    I just ran this on my Iphone and got 454 (02) and 2546 (air)



    Quote Originally Posted by jeffgerritsen  View Original Post
    I have the Android v-Planner version and noticed the Nitrox mixer tools produces incorrect results. For example, starting pressure of zero, finish pressure of 3,000 with a 33 percent O2 says to add 423.4 psi of O2 and 2576.6 of air. However the correct O2 PSI of O2 to add is 455 PSI not 423 PSI.

    How do I know - I missed the question on my PADI Blender test.

    Ross, can you fix that, Please.

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    Re: V-Planner Nitrox mixing tools gives errors in results

    Quote Originally Posted by jeffgerritsen  View Original Post
    I have the Android v-Planner version and noticed the Nitrox mixer tools produces incorrect results. For example, starting pressure of zero, finish pressure of 3,000 with a 33 percent O2 says to add 423.4 psi of O2 and 2576.6 of air. However the correct O2 PSI of O2 to add is 455 PSI not 423 PSI.

    How do I know - I missed the question on my PADI Blender test.

    Ross, can you fix that, Please.
    Actually.. second answer. You might have it set to BAR instead of PSI. That will make difference as the z-factors changes with pressure.
    Ross Hemingway
    ------------------------------------------

    V-Planner PC, Mac, Mobile, iPhone-iPod, Android. MultiDeco Android, PC, Mac.
    V-Planner Live and MultiDeco-X1 for the Liquivision X1 dive computer.
    MultiDeco-DR5 for the DR-5 dive computer.

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    Re: V-Planner Nitrox mixing tools gives errors in results

    Ross,
    can you explain the difference / benefits between z-factors and Ideal method and why you choose z-factors. I thought pressure was pressure?

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    Re: V-Planner Nitrox mixing tools gives errors in results

    Quote Originally Posted by jeffgerritsen  View Original Post
    Ross,
    can you explain the difference / benefits between z-factors and Ideal method and why you choose z-factors. I thought pressure was pressure?
    Hi,

    in reality gasses do not act like ideal gasses, but are compressibile because of pressure, temperature etc.

    To overcome this compressibility the z-factors are used. With their help mixing program can tell you what are real pressures of gasses to be added to achieve desired mixes.

    Igor P

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    Re: V-Planner Nitrox mixing tools gives errors in results

    The ideal gas model was the first mathematical model of how a gas behaves in terms of pressure, volume, temperature and number of atoms (molecules) . It was based on the empirical laws of Boyle and Charles and it can be derived from first principles using some maths called Kinetic Theory.

    The model assumes that a gas is made up of ideal particles that only interact by elastic collision with each other (like balls on a pool table), exchanging kinetic energy (heat). The particles don't attract or repel each other and they have no size, like points in space. If you do the maths, you get the ideal gas equation.

    Real gases behave like ideal gases at pressures below a few atmospheres because the atoms really don't spend a lot of time near each other. However, when you start to compress a real gas towards pressures of tens of atmospheres the atoms or molecules spend more time near each other and start to attract one another. This attraction makes the pressure drop lower than it should be according to the ideal gas law. For oxygen, for example, this difference in pressure is largest at around 200 atmospheres (from memory). If you keep on compressing the gas, eventually it gets so dense that the size of the atoms or molecules starts to matter a lot and the pressure crosses over to being higher than it should be according to the ideal gas law. This cross over happens around 300 atmospheres for oxygen.

    Nitrogen and Oxygen drop below the ideal gas pressure by different amounts and cross over to being higher at different pressures. This is where z-factors come in because they describe more accurately what real gases do.

    For example, if you put 100 atmospheres of Oxygen in a tank you will have more gas in there than the ideal gas law thinks, so when you top up with air your nitrox will not be quite what you want.

    Rich
    Last edited by RichardC; 10th January 2014 at 02:10.

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    Re: V-Planner Nitrox mixing tools gives errors in results

    More about real and ideal gas you can find here: http://thedecostop.com/forums/showthread.php?p=351305

    If you can not acess the link url let me know and I will send you .pdf file.

    Sent from my PAP4500DUO using Tapatalk 2
    Last edited by Igor P; 10th January 2014 at 19:38.

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    Re: V-Planner Nitrox mixing tools gives errors in results

    Folks,
    Thanks for the replies. Quite interesting to read about gas factors. Didn't realize there was that much difference in gas behavior.



    Quote Originally Posted by Igor P  View Original Post
    More about real and ideal gas you can find here: The Deco Stop

    If you can not acess the link url let me know and I will send you .pdf file.

    Sent from my PAP4500DUO using Tapatalk 2

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