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Homework Help: Reynolds Number problem

  1. Sep 11, 2008 #1
    The question gives this ..

    The Reynolds number, Re, is a dimensionless group which characterizes the intensity of a flow. For large Re, a flow is turbulent; for small Re , it is laminar. For pipe flow, Re=u(density)D/mu, where D is pipe diameter and mu is dynamic viscosity.

    It asks ..

    If D and mu are fixed, what is the effect of increasing mass flow rate on Re?
    If mass flow rate and mu are fixed, what is the effect of increasing D on Re?

    Any help is appreciated,

  2. jcsd
  3. Sep 11, 2008 #2


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    Science Advisor

    First of all, while Re is used to characterize the type of flow, it is a ratio of forces in a flowing fluid. It is a ratio of the inertial forces to the viscous forces.

    Start by looking at what defines the mass flow rate...[tex]\dot{m}=\rho*A*V[/tex]

    You'll also need to look at the fact that area is [tex]A=\frac{1}{4}\pi*D^2[/tex]
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