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I Given a fixed volume of pressurized air, calculate the flow rate

  1. Aug 9, 2017 #1
    I have a work related question. Although it seems like a relatively simple question, I am having difficulties finding the correct equation(s) to calculate the answer.

    Question: Given a fixed volume air tank filled with pressurized air, how does one calculate the flow rate over time through an orifice of known size? An example flow rate calculation at maximum pressure would be appreciated.

    Air tank volume is 3.277 cubic liters = 0.003277413 cubic meters
    Orifice diameter = 0.0013208 m
    Air pressure max P1 = 1073.485776 kpa abs
    Air pressure min P2 = 101.325 kpa abs
    Max time for pressure drop from P1 to P2 = 60 sec
    R = gas constant of air = 287 J/kg K = 0.287 kJ.m3/kgK
    air density –ρ = 1.225 kg/m3
    *Temperature = 20C

    *For now, the temperature is assumed to be fixed at 20C even though there will be a reduction in temperature resulting from the reduction in pressure.
  2. jcsd
  3. Aug 9, 2017 #2


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    This is actually a fairly simple problem to do analytically (and the assumptions required to make this true are fairly reasonable). You should look up the concepts of choked flow and choked mass flow rate.
  4. Aug 9, 2017 #3
    Thank you. I will research choked mass flow rate concepts as you have advised. If you have knowledge of publications that are relevant to my specific question, that would be greatly appreciated. Thanks again!
  5. Aug 9, 2017 #4


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    You shouldn't even need publications, per se. Any entry-level textbook on gas dynamics/compressible flow should cover it.
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