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Siphon and bernouli theorum

  1. May 25, 2013 #1
    1. I found this diagram on book but there weren't any description.can someone tell me, what its trying to tell specially by those two red lines meeting the ground at the same place...?
    2.this is a diagram for siphon method of removing water. I have read somewhere that the siphon stops if the pressure at point c is equal to the vapour pressure of water. what is the reason for that.?
    Pc = Po - hρg
    Last edited: May 25, 2013
  2. jcsd
  3. May 25, 2013 #2


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    Staff: Mentor

    Handwritten in a book, with no descriptions? Uh huh....

    The first question would be asking which pair of colored arcs accurately represent the path of water pouring out of that structure.

    For the question on siphons, if the pressure at C equals or is lower than the vapor pressure of water, it boils and no longer can flow up the siphon.
  4. May 25, 2013 #3
    Well, I guess it is just trying to tell you about the water flow. There doesn't seem to be anything aphysical about the diagram at least at first glance and without making any measurements or calculations. The two red lines indicate that the water flow from points symmetrically placed about the center will hit the ground at the same location.
  5. May 25, 2013 #4
    Yes...so whats the physics behind that ? water drains from symetrically placed holes from the center will catch the ground at the same place....?

    all arcs are paths of water pouring.red color shows some special feature..
    further...siphon needs a continuous flow of water.water bubbles disturb the continuous flow...am i correct?
    Last edited: May 25, 2013
  6. Jun 19, 2014 #5
    Apologies if this thread is not exactly germane to my issue but... I have been unable to find information and comment re. the following: If I were to establish a large diameter siphon and have the outflow diameter reduced substantially by attaching a much smaller (but contiguous) tube, would I then be able to have an uphill endpoint for my water flow because the total water mass (and therefore the force exerted) in the "downhill" tube would far exceed that in the smaller "uphill" tube?
  7. Jun 19, 2014 #6


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    Science Advisor

    For this purpose it is height alone that matters, not pipe width. You get the same amount of suction with a 1/8 inch reed on the outlet side as you do with a 36 inch pipe.

    There is a concern that if the pipe is too wide, bubbles can rise up the outflow faster than water carries them down. If this occurs, the water can drain out of the outflow until the siphon no longer works at all.
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