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A Gas (DO) saturation under pressure in water

  1. Sep 12, 2016 #1
    I understand that pure water that's being aerated will only take up just so much dissolved oxygen (DO) and that that depends on the temperature of the water. I see ranges of 14 ppm at close to freezing and around 6 ppm at 50 C as normal maximums.

    I understand, too, that you can temporarily super saturate the water, like via electrolysis, to well above those levels, then over x number of hours, depending on whether it's being agitated or not, it'll inevitably drop back down to normal saturation levels for its given temperature.

    I see tons of, what I'd call, nano bubbles, almost like smoke in the water, from electrolysis rising up and accumulating near and spreading out across just under the water surface, which I assume are the O, and larger bubbles, I assume are H, breaking the surface directly above emitter.

    Please correct me if any of my assumptions above are incorrect or incomplete to fully understanding.

    My question is; If I have a pump inlet pipe near the surface in the thick of those nano bubbles of oxygen and suck them into an accumulator or expansion tank that's being pressured up to 80PSI, that water then would stay, for as long as it's there under pressure, at that higher super saturated DO level, yes?

    And, when I later spray it out through a nozzle into air directly from that pressurized tank to a surface a foot away, what would you guess of how much of that higher saturation DO % in the water would be lost to the air and not still retained in the water spray mist hitting that surface?

    IOW's, lets say we'd sucked in and started at 30ppm DO super saturated water under pressure and normal saturation for water was 10ppm for our temperature, how much, would you guess, would still be in the water that hit the surface a foot away and not already lost in the foot of air after it came out of the nozzle? Assume, too, that nozzle, if it makes any difference, was emitting that DO super saturated water at 50-100 microns.

    Thank you for any thoughts.

    - Shane
    Last edited: Sep 12, 2016
  2. jcsd
  3. Sep 12, 2016 #2


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    Yes, if the pressure was high enough to keep the particular volume of gas dissolved in the particular volume at the temperature its being held at.
    Each temperature and pressure will have a maximum concentration of gas it can hold at equilibrium. The total amount of gas will be the product of the equilibrium concentration and the volume. That would be the determining factor. If there was more gas than that it would come out of solution.

    The rapidity of the dissolved gas concentration in a body of water returning to its equilibrium concentration for those conditions will depend on things like the amount of surface area of the water-air interface and the amount of turbulence of the water.
    Various kinds of gas exchangers will have different rates of doing this. A trickle tower is supposed to get the water flowing through it to equilibrium after falling 4.5 feet. It would probably be faster if there was a counter-current flow of atmospheric air. The engineering details matter. A sprayer with very small droplets would probably be very efficient at getting to this equilibrium. It would expect it to be close to if not at equilibrium. Smaller bubbles would make it faster.
  4. Sep 12, 2016 #3
    BillTre, thanks for that, appreciate the comments.

    Ordered DO meter, already have everything else in place, will see then what the after nozzle spray fluid run off shows it to be.

    This is for aeroponically and intermittently (5 seconds on, 5 minutes off) misting of roots in a mostly sealed up enclosed barrel.

    I'm guessing if I'd earlier captured and then later delivered to the nozzle super saturated DO water, whatever does not then get
    to the roots in the water, escaping in the spray, will, at least, raise O2 air levels within the barrel. That's also good for the roots
    and for any later fluid spray cycles that have below saturated DO levels to pick up some additional DO themselves then, too,
    with it being sprayed into and through that now O2 enriched air accumulating in there.

    That's the plan anyways...

    - Shane
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