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Homework Help: Venturi meter with 2 tubes

  1. Nov 21, 2009 #1
    1. SFL_be.jpg

    Find , the speed of the fluid in the left end of the main pipe.
    Express your answer in terms of h_1, h_2 , g , A_1, A_2.

    2. Bernoulli and continuity equations

    p_1 = rho*gh_1
    p_2 = rho*gh_2

    p_2 = p_1 + 0.5rho*v_1^2 + 0.5rho*(A_1/A_2)^2 * v_1^2

    I know those are correct.

    Substituting for p_1 and p_2, and solving for v_1 I obtain:

    2g(h_2 - h_1) / [1-(A_1/A_2)]

    all that under a square root.

    No idea why I am getting it wrong. Should h_2 - h_1 just be h??
  2. jcsd
  3. Nov 21, 2009 #2
    Yeah, I am totally stuck on this one. Solving for V_1 I get the following, and I don't see where I could have made a mistake:

    v_1 = sqrt[2g(h_2 - h_1) / (1-(A_1/A_2))]
  4. Dec 8, 2009 #3
    :D this question had me stumped for a bit but ur equations helped a bit ... sorta >.>

    kk First i got my own equations xD lol


    from this we get that v2=(v1A1)/A2

    P1-P2=[tex]\rho[/tex]/2* (v2-v1)

    Now sub in v1 for v2

    this gives us
    P1-P2=[tex]\rho[/tex]/2* ((v1A1)/A2-v1)

    Now do a little math ... >.> well maybe not a little

    but you'll get that v1=

    sqrt( (g(h1-h2)) / ((A1/A2)^2-1))

    o.o' wish i knew how to code that up so it would look pretty

    but the only difference between this and your answer is in the demoninator

    first off the A1/A2 part is supposed to be squared

    and ur signs are backwards :D hope this helps ^^

    o.o ... now to go back and make this reads properly
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