Compressible Flow, Pressure and Mass Flowrate

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SUMMARY

This discussion focuses on compressible flow through rotameters, specifically examining the relationship between pressure and mass flow rate. The experiment involves an upstream and downstream rotameter with a needle valve acting as a fixed orifice. It is established that above 13 psig, the flow becomes sonic, resulting in a linear relationship on the graph, while subsonic flow does not follow a predictable curve. The concept of "choked flow" is crucial for understanding these phenomena.

PREREQUISITES
  • Understanding of compressible flow dynamics
  • Familiarity with rotameters and their operational principles
  • Knowledge of pressure measurement units, specifically psig
  • Basic grasp of flow rate calculations and graph interpretation
NEXT STEPS
  • Research "choked flow" and its implications in compressible fluid dynamics
  • Study the behavior of rotameters at varying pressure conditions
  • Explore the mathematical models governing compressible flow
  • Investigate the effects of fixed orifices on flow characteristics
USEFUL FOR

Students and professionals in fluid mechanics, engineers working with flow measurement devices, and anyone involved in laboratory experiments related to compressible flow dynamics.

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

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