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Mass Flow Rate of Pressure Regulator

  1. Oct 11, 2016 #1
    Hey,

    I have an air tank that is at a set pressure, say 3000psi, and I have attached a regulator to the end that regulates the pressure down to 800psi. As the valve on the tank is opened the pressure and the mass in the container will decrease. If there was no regulator the mass flow rate would also decrease until flow stopped when atmospheric pressure is reached.

    Will the mass flow rate through the regulator remain the same provided the tank is above 800psi? Or will the mass flow rate decrease as it would without a regulator?

    I'm hoping to come up with a way that outputs a constant mass flow rate and therefore constant thrust force through a nozzle attached to the end of the tank.

    Cheers
     
  2. jcsd
  3. Oct 11, 2016 #2
    Hi,
    You'll need a digital mass flow controller for that application,as for your question yes the mass flow rate will remain the same with your set condition because a mass flow controller has an attached inlet-loop and sensor which senses the current pressure and then opens or closes the variable outlet valve accordingly,thus,the mass flow rate remains the same.
     
  4. Oct 11, 2016 #3

    Nidum

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    Science Advisor
    Gold Member

    @Andr5w5

    Sorry but you can't just guess your way through a problem like this .

    You need to have information about the actual characteristics of the valve and of the nozzle .
     
  5. Oct 11, 2016 #4

    JBA

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    As stated above, as long as your tank pressure remains above the pressure regulator's required inlet pressure for an 800 psi set pressure the flow will remain constant.

    In selecting an appropriate pressure regulator you must also select one with a specified maximum designed flow rate greater than that of the design flow rate of your nozzle.

    A simple tank discharge design consisting of a pressure regulator feeding a volume chamber ahead of your nozzle will do what you want (the chamber is to provide a bit of the pressure recovery and stabilization between the regulator discharge stream and the nozzle inlet).

    What will also affect the time of the flow and thrust is the rate at which the tank pressure is reduced because this will result in a depressurization temperature/pressure drop in the tank as well. Unfortunately, for your type of application the amount of temperature/pressure reduction during the flow cycle cannot be exactly calculated by the using only the classic adiabatic gas cooling formula because it is controlled by the combination of adiabatic cooling and the heat transfer rate through the tank wall during that time (this is technically known as a polytropic process). However for short flow times the adiabatic formula should still give a very good estimate.
     
    Last edited: Oct 11, 2016
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