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Mass flow rate through a regulator

  1. Oct 7, 2016 #1

    We have a canister at a set pressure (4500psi) full of compressed air. A single stage pressure regulator is fitted to the canister that reduces the outlet pressure to 850psi. The flow from the regulator is then used in a divergent nozzle to create a thrust force capable of lifting a small mass (2-3kgs). I understand that the mass flow rate is not constant and have obtained graphs using thrust equations for 4500psi with no regulator. The graphs take into account the fact that the mass flow rate and pressure decrease as the canister empties and from the graphs this shows a logarithmic decrease in the thrust generated. Is there a way to calculate the mass flow rate (and therefore the thrust) for the system with a regulator involved?

    After the output pressure drops below the 850psi we would shut off the system remotely.
  2. jcsd
  3. Oct 8, 2016 #2


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    As long as the tank pressure is above the required inlet supply pressure to the regulator at the regulator's 850 psi set pressure then the mass flow will be constant and equal to the value shown on your graph when the tank pressure is equal to the set pressure of your regulator, assuming the combined regulator and nozzle flow coefficient is the same as the nozzle coefficient used for the tank flow calculation without the regulator.
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