Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How to get water in air tight container w/ other specifics

  1. Sep 22, 2009 #1
    Let's say i have a sealed container with half water, half air, and i would like the air pressure to remain constant. how can i get a water hose to pour into this sealed air container without having the air escape up the hose?

    Note* There is water leaving my container at the same rate it would be entering - so no need to worry about the water affecting the air pressure.


    see attached image

    also, let me know if there is a way to do so with an alternate outlet and inlet configuration

    Thanks
     

    Attached Files:

  2. jcsd
  3. Sep 22, 2009 #2

    Cleonis

    User Avatar
    Gold Member

    What you would need is a self-regulating way to pre-pressurize the water supply so that it matches the pressure inside the container.

    This reminds me of the way that in the 1940's the frenchman Cousteau developed a diver's air supply unit, now known as scuba gear. (Until then divers on extended dives were dependent on air supply via a socalled 'umbilical'.)

    In Cousteau's case a self-regulating valve system had to be devised that would reduce the pressure of the air inside the air cannisters to the pressure at the current diving depth. That is, at a depth with an ambient water pressure of 2 atmosphere the scuba gear had to offer air pressure at 2 atmosphere to the diver, and so forth.

    The system that pre-pressurises the water supply for the cannister that you describe will have to do something similar.

    Cleonis
     
  4. Sep 22, 2009 #3

    russ_watters

    User Avatar

    Staff: Mentor

    If the water is coming from a valve, air will not escape up the hose*: there is nowhere for it to go.

    *...in any quantity larger than the volume of the hose.
     
  5. Sep 22, 2009 #4
    What do i mean by "...in any quantity larger than the volume"?

    I'm not sure if i understand.

    so no matter what the pressure of the incoming water is, the air won't be able to escape?
     
  6. Sep 22, 2009 #5

    DaveC426913

    User Avatar
    Gold Member

    Am I missing something? If the entry and exit hose are in the bottom of the container, the water can flow in and out without disturbing the bubble of air at the top of the container.
     
  7. Sep 22, 2009 #6

    russ_watters

    User Avatar

    Staff: Mentor

    If the water is coming from a valve, like a garden hose, the water in the garden hose can spill out into the container, depending on if the orientation of the hose allows it. You can try this at home - if you slope a garden hose, water will spill out of it after you turn it off at the faucet.
    Air can't go backwards past the valve where you turn the water on.
     
  8. Sep 22, 2009 #7

    russ_watters

    User Avatar

    Staff: Mentor

    Yes, that would be a simple solution to the problem.
     
  9. Sep 22, 2009 #8
    Ok. thank you everyone. i guess i must have been over thinking this.

    I am quite glad that i stumbled accross pf.

    speeddman
     
  10. Feb 12, 2010 #9
    I just tested this system. unfortunately bubbles went up my hose. the water from the hose is sitting in a container open to air. i don't know what to do
     
  11. Feb 12, 2010 #10

    DaveC426913

    User Avatar
    Gold Member

    Go have a drink.
     
  12. Feb 13, 2010 #11
    ummm, first thing I thought of was the old camping coffee pot my grandfather made according to him during WW2.

    It was a cylinder with one fitting that was about 1/4 of the way from the top or just below the water line. it came out and made a 90* turn up to just above the top. at the other side of the cylinder was another fitting like the first but it was about 1/4 of the way from the bottom, the pipe exited at 90* made it's way to the top and then arc'd over like a big tea spout.

    here's the genius in it. fill it up leaving an air space in the can but a water line in the pipes. place on the fire and once it's near a boil remove to a cooler but still hot spot of coals and when ever you need hot water, pour cold water into the top pipe and an equal amount of hot water will pour out the other pipe. no need to constantly heat water in large batches.
     
  13. Feb 13, 2010 #12
    Hot water heaters operate under the same principle.
    Ohh and I got the pipe arrangement backwards, it's been 30yrs. the cold water feeds into the lower end.
     
  14. Feb 13, 2010 #13
    here's a quick model in solidworks for you...
     

    Attached Files:

  15. Jul 7, 2011 #14
    A backflow preventer is a commercial solution and they are designed to do just this. Basically, the idea is that by passing the water through an expansion valve, you create a pressure drop which will not allow fluid/air to pass back into the line. These are available for relatively cheap in a hardware store and are required on all outdoor hoses in commercial buildings to keep chemicals out of the public water supply. Also, a water trap (like is found under a kitchen sink) is designed to do the same thing. Water can pour into the sewer but gases from line cannot come back into the house. Much the same as the water heater described above.

    --------------
    www.cfdengineer.com
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: How to get water in air tight container w/ other specifics
Loading...