1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculation for knowing duration of gas cylinder

  1. May 27, 2015 #1
    I know the total volume of a gas cylinder, the pressure in it, and the outlet pressure that needs to be maintained. The flow rate is also known. How should I calculate the total duration the cylinder will last? Also, what should vary if the cylinder is a liquidified gas cylinder?
  2. jcsd
  3. May 27, 2015 #2
    PV = nRT

    Knowing the flow rate at some given pressure and temperature you should know the number of moles of gas leaving the cylinder per second ( or minute or hour, what ever unit of time your flow rate is in). Also, you know the number of moles of gas in the cylinder if given the initial temperature, volume, and pressure of the gas.

    If stuck on a problem like this write down the equation you are likely to use and then write down what you know.
  4. May 27, 2015 #3


    User Avatar
    Science Advisor
    Gold Member

    The answer here depends on a few things. For starters, you need to know the geometry of the outlet and the pressure ratio of the outlet pressure to ambient pressure. You also will need to know the temperature of the gas in the bottle (and decide whether or not you want to assume it is constant or assume the system is adiabatic, etc.). Depending on the assumptions and operating parameters, this can be a very simple problem or a very complicated one.
  5. May 27, 2015 #4


    User Avatar
    Science Advisor

    Welcome to PF.
    Only the mass of gas remaining will give you a longer term prediction of empty than will gas pressure.
    You will need to weigh the empty cylinder or read the tare mark to know where zero will be.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook