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Would this work to pump water ?

  1. Apr 3, 2013 #1
    I was browsing gardening youtube vids and something sparked an idea.

    The idea is to pump a small amount of water, up a short distance, without using any electric or mechanical energy input.

    pic 1.

    There is a sealed container (ie: big bottle) with a small diameter (1/4 inch) tube fed into the container.
    The container is filled with half air and half water.
    The container is painted black to absorb solar energy and cause it to heat in the sun (maybe to 100-120 degrees).

    How would one calculate what height the water would it reach, in the tube, based on temperature increase?

    pic 2.

    In this pic i theorize that if provided with one way check valves (drawn in green), it would work until there is no water left in the tank, due to the varying temperatures during day/night.
    Though i believe the one way water valve might need to be placed below water level inside the container (although i drew it above it)

    Can this be proven theoretically to work?
    Last edited: Apr 3, 2013
  2. jcsd
  3. Apr 3, 2013 #2
    In retrospect, i realize that no one would want 120 degree water to water their plants, but in the picture my idea is simplified.
    The volume of air and water could be separated, ie: in 2 connected containers, so that only the air is being actively heated by the sun, resulting in the pressure rise pushing the water up from the other container.
  4. Apr 3, 2013 #3


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    Yeah, I guess this would work, as long as the temperature rises and falls in a cycle.
  5. Apr 3, 2013 #4


    Staff: Mentor

  6. Apr 3, 2013 #5
    How can i calculate how far would the water rise, based on the example data?

    @Dale, The driving force would be the expansion of air......the water would not be vaporized too much... specially if the air part and the water part are kept separately.
  7. Apr 3, 2013 #6


    Staff: Mentor

    Oh yeah, I forgot about that. You can calculate that driving pressure using the ideal gas law.
  8. Apr 3, 2013 #7


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    Staff: Mentor

    You should do a comparative calculation to see if it would be more efficient to use solar cells to generate the energy for the pump. Since you are assuming insolation to drive your thermal pump mechanism, it's reasonable to compare the efficiencies, IMO.
  9. Apr 4, 2013 #8


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    Assuming you're trying to create a solar powered pump using air, then it seems that it would be better if you had additional valves to allow the heated air to exit the chamber and for cooler ambient air to enter the chamber on each cycle.
  10. Apr 4, 2013 #9


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    Perhaps experiment with old car tyre valves? They are normally discarded when tyres are replaced so you might get some free.


    Imagine it's cold/night and the unit has just filled with air. The air inlet valve will (hopefully) close when the pressure inside becomes slightly greater than atmospheric/outside so that gives you a rough starting pressure, volume and measured temperature.

    Given the temperature in PV=nKT is in kelvin the change in PV due to a change in T won't be huge. So a big tank will be needed to pump a small volume.
    Last edited: Apr 4, 2013
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