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Thread: Equivalent Air Density Depth (EADD)

  1. #11
    Mr Cheesebox edster will become famous soon enough edster will become famous soon enough edster will become famous soon enough edster's Avatar
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    Re: Equivalent Air Density Depth (EADD)

    An additional question which may be completely irrelevant, or not - but here goes :

    Is the viscosity of the gases significant to take into account - and if so, then you might need to consider the temperature of the gas that you use. After all if a 10deg C change makes water half as viscous, then I would assume that it has at least some effect on other fluids. Unfortunately I can't add much more than that, but perhaps someone else can take up the baton?

    cheers

    Ed

  2. #12
    RBW Member Tim Cashman is on a distinguished road Tim Cashman is on a distinguished road Tim Cashman's Avatar
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    Re: Equivalent Air Density Depth (EADD)

    Quote Originally Posted by koputai
    Seems like a good time to rehash this:
    http://www.deepdiving.net/rants/norcotic.html

    Just use norcotic trimix Steve.

    Jason.
    Excellent concept. Heres an additional twist.

    Daltons law states that the pressure of a gas mixture is the sum of the partial pressures of the component gases.
    Henry's law states that the solubility of a gas is directly proportional to its pressure.

    If we use trimix 10/70/20 at 90m the ppO2 = 1bar, ppHe = 7 bar, ppN2 = 2 bar right?

    Henrys law states the gas dissolved in the liquid is proportional to these individual pressures, so O2 gets metabolised and isn't a primary concern, He dissolves to the tune of 7 bar x time, N2 dissolves to the tune of 2 bar x time.
    If we vary these individual pressures by changing the mix we will vary the "driver" that causes the gas to dissolve?
    I generally use nitrogen at max 20% because it is manageable narcotically and from a density WOB point of view on deep dives, plus it means the helium is not so close to saturation as it would be if I used "norcotic trimix", so in principle I am less saturated with He.
    Too much N2 means bends, narcs and high WOB.
    Too much He means bigger risk of a He bend and the willies.
    Adjust the proportions for optimum effect.

    With me in principle? here comes the twist.
    IF it were possible to use 10 different inert gases! (decamix?) each one at say 10%, none of the individual gases would exceed a pp over 1 bar at 90m and the "driver" which causes them to dissolve, would be substantially reduced, - maybe to a "no stop" saturation level !!!
    IF this were possible could decompression be avoided altogether ?!?
    Unfortunately there aren't enough inert gases with the appropriate properties for a diluent.
    Quadmix maybe??
    Gives yer brain a workout doesn't it?
    Tim

  3. #13
    New Member Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell's Avatar
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    Re: Equivalent Air Density Depth (EADD)

    Quote Originally Posted by Tim Cashman
    IF it were possible to use 10 different inert gases! (decamix?) each one at say 10%, none of the individual gases would exceed a pp over 1 bar at 90m and the "driver" which causes them to dissolve, would be substantially reduced, - maybe to a "no stop" saturation level !!!
    IF this were possible could decompression be avoided altogether ?!?
    Unfortunately there aren't enough inert gases with the appropriate properties for a diluent.
    Quadmix maybe??
    Gives yer brain a workout doesn't it?
    Tim
    Gidday Tim, long time no hear!!

    Sorry to rain on your parade but applying your own excellent explanation of Dalton's law, you will appreciate that at the end of a dive with your ten gases, the total pressure of gas in a tissue will equal the sum of the partial pressures.

    For a bubble to grow, the following condition must be satisfied:

    Ptiss > Pamb + ((2 x surface tension) / bubble radius)

    Where: Ptiss = total gas pressure in the tissue
    Pamb = ambient pressure

    Since Ptiss includes the sum of partial pressures of all inert gases in the tissue, it doesn't matter if you have created a situation where the partial pressures of the individual gases are low by breathing 10 gases. If you add them together and Ptiss satisfies the above condition then you are no further ahead.

    Good to see you around here.

    Warm regards,

    Simon M
    Last edited by Simon Mitchell; 6th December 2005 at 00:19.

  4. #14
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    Re: Equivalent Air Density Depth (EADD)

    Hi Tim,
    Interesting theory. You first


    I'm, at heart, skeptical about the free lunch this idea suggests might be on offer and I have the feeling that there might be some cummulative effect on vapour pressure in tissues and hence your bubbles will just have 4 different inert gasses instead of the usual two. If this is not right maybe your idea has merit?

    Cheers.
    AB


    Edit: Ahh, there you go...thanks Doc.

  5. #15
    RBW Member Tim Cashman is on a distinguished road Tim Cashman is on a distinguished road Tim Cashman's Avatar
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    Re: Equivalent Air Density Depth (EADD) - "Multimix"

    Hi Simon Howzitgoin?
    (Read Keiths book Deep Water Gold? He did a good job of it. Your on pages 182 and 229!)

    Re "Multimix"
    I'm sure you're right or someone would have used this concept by now.
    The concept is purely the physics of gases dissolving in liquids and what drives it.

    Henry's Law was the twist.
    Each component gas goes in or out of solution in proportion to the pp of itself vs the saturation of itself?
    ie it goes in and out of solution independently of its neighbours?

    I was theorising if there was an ideal balance of gases what could it be?

    I take your point though, that if there is a 10 ata ambient and 10 gases all at pp of 1 bar you still get 10 bar total and what goes in must come out again.
    10 bar in = 10 bar out later; irrespective of whether it is a multiple gas mix or a single gas.

    Pub!

    Tim
    Last edited by Tim Cashman; 7th December 2005 at 22:25.

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    New Member Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell's Avatar
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    Re: Equivalent Air Density Depth (EADD) - "Multimix"

    Quote Originally Posted by Tim Cashman

    Pub!

    Tim
    Mate!

    The smartest thing I've read on any forum for ages!

    Simon

  7. #17
    New Member jonas isaksen is an unknown quantity at this point jonas isaksen's Avatar
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    Re: Equivalent Air Density Depth (EADD)

    Quote Originally Posted by Steve  View Original Post
    In this thread http://www.rebreatherworld.com/technical-rebreather-forum/2289-new-v-planner-3-70-a.html I asked Ross if he could include and EADD calculation into V-Planner. Ross has PMed me and thinks the idea has some merit.

    OK here is the bit about my bright idea I just donít know much about. How deep an EADD is too deep? I think itís important to at least be aware of this as breathing too dense a mix at depth can easily predispose one to CO2 accumulation. Gas selection is not just about ppO2 and narcosis. A figure indicating the equivalent resistance of breathing air when diving very deep dives would be handy to know.

    What is a meaningful number?

    To save you reading the other thread here is a bit of a cut and paste to summarise what Iím on about.

    Iím after a feature that provides an Equivalent Air Density Depth (EADD) ie breathing 5/80 @ 150m is like breathing air @ 'x' m

    This would be of particular use for very deep dives when factoring in gas breathability V's EAD V's CNS V's Deco considerations

    As far as I know (please don't hold me to this) its a straight forward case of gas % x gas density at STP x pressure at depth = density at depth
    Density of individual gases in kgs/m3 at STP is
    O2 1.429
    N2 1.250
    He 0.179
    CO2 1.977

    eg density of air at 40m (O2 + N2)
    (1.429 x 21% x 5ata) + (1.250 x 79% x 5ata) = 6.438 kgs/m3

    eg 2 density of trimix 5/80 at 200m (O2 + He + N2)
    (1.429 x 5% x 21ata) + ( 0.179 x 80% x 21ata) + ( 1.250 x 15% x 21ata) =8.4375 kgs/m3

    Which gives an EADD of 58m

    Might be due to ignorance, however the transition from 8.4375Kgs/m3 to 58 meters is something in my theoretical education that has become lost. Is it possible to have the transition explained as well?

  8. #18
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    Re: Equivalent Air Density Depth (EADD)

    (1.429 * 21% * xata) + ( 1.250 * 79% * xata) =8.4375 kgs/m3
    -> .3009*x ata + .9875* x ata = 8.4375
    -> (.3009+ .9875) * x ata = 8.4375
    -> 1.2884 * x ata= 8.4375
    -> x ata = 8.4375/1.2884
    -> x ata = 6.576
    D(m)= (D(ata)*10)-10
    -> x (m) = (6.576*10)-10
    -> x (m) = ~56

    i suspect some rounding errors to account for the difference.

    "state of origin" rugby league here tonight so lots of piss being drunk
    rachel

    GO QUEENSLAND!

    .....OR
    This would have been easier to type and quicker to work out:
    GIVEN (1.429 * 21% * 5ata) + ( 1.250 * 79% * 5ata) =6.438 kgs/m3
    AND (1.429 * 21% * xata) + ( 1.250 * 79% * xata) =8.4375 kgs/m3
    the equation becomes a ratio.
    -> x ata= 8.4375/6.438 * 5 ata
    -> x ata = 6.552
    -> x m =~56m
    Last edited by bendomatic; 4th July 2007 at 21:49.

  9. #19
    RBW Member kes is an unknown quantity at this point kes's Avatar
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    Re: Equivalent Air Density Depth (EADD)

    I don't think this is quite the best way to do this. It's comparing breathing air with breathing your dilluent. That might be useful, but when I do this calculation I compair breathing air diluent at a set point of 1.3 with the depth and trimix I'm using at my maximum depth and a set point of 1.3. The difference with my approach is it allows for the change in gas mix you actually breath after the rebreather changes the mix to give the required set point, so makes a comparison that is easier for me to compair with the way air dill feels to breath in my particular rebreather not a comparison to open circuit.

    In terms of the the unit you use to make the comparison, is the density in metric, imperial units etc, its not that important as your doing a comparison the units cancel out. Looking at avagadros law, at low pressure(is an ideal gas) a given volume of gass at a given pressure has the same number of molecules in it, so you can PROBABLY just use the molecular mass of the gas. Note this is not the same as the atomic mass.

  10. #20

    Re: Equivalent Air Density Depth (EADD)

    As we have a stable 2.x now I'd like to come up with a previous discussion started in Web Designing Training in Chennai

    In the custom view for EAD/END there is ppO2 displayed which - for CCR usage - covers the part of O2 in the loop contributed by the diluent, which is uncommon and IMHO of no use. Do others think the same? Web Designing Training in Chennai

    As the diluent ppO2 (which is important to know) is already shown on the main screen (triggered by CF settings) there is no need to show an (other) ppO2 in the custom view. A more related value to the already displayed EAD and EAN would be EADD - Equivalent Air Density Depth. This would be a similar value as EAD and END and would match in this custom view perfectly.

    Would like to here your feedback on this . PHP Training in Chennai

    Just to make clear: This is not a personal request by me but an idea to be discussed to improve the unit further.

    Thx,

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