Calculate the flow velocity

  1. Jul 7, 2013 #1
    This might be simple but I can't remember how to do it.

    problem: we have 2 tanks. One filled with atmospheric air at 1 bar and the other is vacuum. The two tanks are connected by a rigid pipe which has a valve. I open the valve and air flows to the vacuum tank. How do I calculate the air velocity?

    P.s: I don't think Bernoulli is valid here because the flow isn't steady I guess. Please state your assumptions clearly.

    Thanks in advance
  2. jcsd
  3. Jul 7, 2013 #2


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    Flow velocity depends on the thickness and length of the pipe, and on the temperature of the air.
  4. Jul 7, 2013 #3


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    Instead of 'thickness' of the pipe, the term 'internal diameter' would be more apt.
  5. Jul 7, 2013 #4


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    Also pay attention to the pressures. The flow is going to start off choked but will eventually un-choke as the pressures equalize.
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