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air (O2 N2) in liquid water.

Babin Member Posts: 2
As we heat water in a liquid filled ( all free air in pipes removed) hydronic system we release air in soution. The fill water at 70 deg F has how much air in solution as a percentage? and how much of that air can I expect to drive out of the solution after heating it to 180 deg F. Wondering if someone can give me an answer to this question. Thank you.


  • icesailor
    icesailor Member Posts: 7,265
    Air ratios:

    I can't give you an answer because what you are getting rid of when you heat the water is removing dissolved gasses in the water. How would you know who many, gasses are in the water and what ratios.
  • remodel
    remodel Member Posts: 68
    partial pressures

    I am no chemist or thermo-engineer but you might be getting into partial pressures and mols etc.. Might be some assumptions (temp, pressure, fluid type) that can be used and equations out there to balance.
  • SWEI
    SWEI Member Posts: 7,356
    It depends on pressure as well as temperature

    Here's a handy chart from p.7 of Idronics #2
  • icesailor
    icesailor Member Posts: 7,265

    So what IS air?

    20%+/- oxygen, 80%+/- nitrogen and other small amounts of gasses. Like CO2.

    Water is H2O, two parts hydrogen, one part Oxygen. Does all the nitrogen etc. boil away?
  • SWEI
    SWEI Member Posts: 7,356
    In a closed system

    The oxygen eventually does "go away" by reacting with metals and other materials in the system.  You basically end up with nitrogen, either dissolved or in a bubble (in the case of a non-bladder expansion tank.)
  • hot_rod
    hot_rod Member Posts: 19,860
    some additional reading

    on air, and it's removal in hydronic systems.

    It's critical to get all the air, especially micro-bubbles from hydronic systems. The heat exchange efficiency, boiler, tube and emitters, depends on air free fluid in the system.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • icesailor
    icesailor Member Posts: 7,265


    I had a discussion yesterday with someone who told me that water won't freeze if it contained Nitrogen. Actually, it was a one sided discussion. He was right, I was wrong. I hadn't thought about what you just said. If all the Oxygen is gone from the water, and there is no nitrogen in the water, I guess that's how the water freezes in a heating system and break the pipes. How does this happen? Does some gremlin get inside the pipes and split them? If the Oxygen and Nitrogen are all gone, does it mean that I could use the remaining Hydrogen water to power my truck?

    Inquiring minds ponder these things.