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Homework Help: Fluid Dynamics Help

  1. Jun 9, 2007 #1
    I understand the concept of this question, I think, but I don't know how to go about getting an answer.

    A tank is completely full of water with no air. A valve at the bottom is opened, while one on top remains closed. What is the lowest pressure that the tank will reach. From valve to valve the height is 30ft.

    I understand that as the water drains, it will pull a vacuum inside the tank, which will eventually collapse at a low enough pressure. I also know that the water will vaporize at some point due to the lack of pressure in the tank, but I don't know if they want the vapor pressure (no temp was given) or if there is some calculation to do.

    Any guidance is appreciated!
  2. jcsd
  3. Jun 11, 2007 #2
    For anyone who is wondering, I found out the answer. You assume atmospheric pressure pushes up into valve B, so the pressure in the tank is 14.7psi-(rho)gh where rho is the density of water, g is gravitational accel. (32.2ft/s^2), and h is 30ft. The point was that on the second part (h=40ft), the minimum pressure is below the vapor pressure of water, so the vessel is not possible at that height.
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