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Compressible Flow, Pressure and Mass Flowrate

  1. Feb 14, 2015 #1
    I am doing a lab report and it is to do with compressible flow through rotameters. An upstream and downstream rotameter to measure flow rate with a needle valve between the two. The needle valve acts as a fixed orifice in one part of the experiment. Then the inlet pressure is altered.

    Plotting pressure against mass flow rate yields a graph where above 13psig the flow is sonic and it follows a straight line. However at subsonic speeds it no longer follows a curve. I am struggling to explain why this is the case?

    Any ideas?
  2. jcsd
  3. Feb 14, 2015 #2


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    Science Advisor
    Gold Member

    Google "choked flow." That ought to set you down the right path.
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