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Flow of water in a venturimeter

  1. Sep 6, 2012 #1
    1. The problem statement, all variables and given/known data
    Water flows in a horizontal venturimeter. the diameter is 100 mm, and the throat is 50 mm.
    The pressure at the entrance is 0.65[bar].
    What is the maximum throughput that is allowed so that the absolute pressure in the throat will not drop under 0.3[bar]

    2. Relevant equations
    Bernoully equation:
    [tex]H_1+\frac{V_1^2}{2g}+\frac{P_1}{\gamma}+H_P=H_2+ \frac{V_2^2}{2g} +\frac{P_2}{\gamma}[/tex]

    3. The attempt at a solution
    The velocity V2 in the throat:
    [tex]V_2=V_1 \frac{0.1^2}{0.005^2}=4V_1[/tex]
    Bernoully equation:
    [tex]\frac{0.65E5}{1E5}+\frac{V_1^2}{20}=\frac{0.3E5}{1E5}+\frac{16V_1^2}{20}[/tex]
    Which produces negative velocity.
    Even if i use absolute pressures, the same. i use 1.65 instead of 0.65.
     
  2. jcsd
  3. Sep 6, 2012 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Hi, Karol.

    I don't see how you're getting a negative velocity here.

    Also, are you sure that your value of [itex]\gamma[/itex] is correct?
     
  4. Sep 7, 2012 #3
    you are right!
    Thanks...
     
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