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Homework Help: Dimensional Analysis problem - choosing variables

  1. Nov 4, 2014 #1
    1. The problem statement, all variables and given/known data
    Hello guys!

    I have a dimensional analysis problem where water is draining from a open topped tank and in a certain amount of time,t it drops from h1 to h2. and I need to find a bunch (6) of variables which apply to this problem. I have some but Im not sure about the other ones.

    2. Relevant equations
    I have to present my answer as deltaH (the change in height from h1 to h2) / d (the size of the hole from which water is flowing) = f(?,?,?)

    3. The attempt at a solution

    I have chosen, the time it takes for the water to drop from a level, h1 to a level h2.

    the diameter of the tank

    the diameter of the hole which the water is draining from, which is on the floor of the tank in the middle.

    the density of the water

    and then the last two I'm not sure about. (It says its not viscous so I don think I can use that)

    I chose g, gravity as I think that might effect flow
    and P the pressure, which I am taking is the air pressure. [I think its possible exit velocity of the water should replace this but I'm really not sure.

    this gives me:

    delta H (the change in height from H1 to H2) = f(t,D,d,P,g, rho)

    Could you guys give some advice about which equations I should use?

    Thanks very much!
  2. jcsd
  3. Nov 9, 2014 #2
    Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Nov 10, 2014 #3
    Why don't you just solve this problem using Bernoulli's equation first? This will give you all the parameters involved, and then you can back out the dimensionless groups from that solution.

  5. Nov 10, 2014 #4
    Ive never heard of Bernoulli's equation, ill have to check it out!
  6. Nov 10, 2014 #5
    Hi everyone, thanks for posting, I've managed to do it but thanks for posting. I've never been told about Bernoulli's equation so I'll have to check it out, it sounds very useful if it can give you the variables! Thanks! :)
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