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Fluid Mechanics, help!

  1. Jan 23, 2006 #1
    When a fluid flows through a sharp bend, low pressure may develop in localized regions of the bend. Estimate the minimum vapor absolute pressure in psi that can develop without causing cavitation if the fluid is water at 160 F.

    How does one calculate the vapor pressure of water when given a temperature? Thanks.
  2. jcsd
  3. Jan 23, 2006 #2
    I can tell you from a handbook that the VP of water at 160 is 10.9 ft of water = 4.73 psi and at 212 it is 33.9 ft of water.
  4. Jan 25, 2006 #3


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    I must say that I can't remember ever having to calculate the vapor pressure of something, unless it was a mixture. I'd have to say that I would simply look it up in a table and be done with it.

    I am sure there are some thermosynamics texts that would show some correlations.
  5. Jan 25, 2006 #4


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    Staff: Mentor

    As Fred mentioned, check a thermodynamics text. The only way one can have vapor with a liquid of the same compound is if the mixture is a saturation conditions. So what one would look for is the saturation pressure of water at 160°F.

    Ideally water is transported as a compressed liquid, but there the pressure drops along a pipe by friction and when changing direction (momentum) in a fitting, e.g. an 'L'. For a piping system to transport liquid the lowest pressure is obviously at the end, and if the fluid is to remain a liquid, the lowest pressure must be greater than the saturation pressure. This assumes that there is not heat input into the pipe or fluid transport system.
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