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Homework Help: Pressurized Gas Canister Release Question

  1. Jul 20, 2007 #1

    I have 2 pressurized canisters, both are 60 litres in size. Both are filled with 120 litres of ideal gas. Canister A is heated to 100 degrees celcius (373 kelvin) and Canister B is heated to 2000 degrees celcius (2273 Kelvin).
    Canister B will obviously expand more than Canister A.
    But, I have a few questions.
    If both canister valves are opened to release the gas, which canister will empty first? Canister A that has lower volume of gas and lower pressure or Canister B that has larger volume and higher pressure?

  2. jcsd
  3. Jul 20, 2007 #2


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    Staff: Mentor

    Assuming the canisters don't expand much (so their volume difference is isn't much and the pressure is high), canister B will be at much higher pressure and will therefore expel it's gas faster on a per mass basis.
  4. Jul 20, 2007 #3
    initial pressure and volume in both canisters are same(not different as you say).
    after the heating, pressure of can B will be obviously more. therefore canister B will empty first.
  5. Jul 20, 2007 #4


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    How can two identical containers, with the same amount of gas in them, at two different temperatures have the same pressure?

    Are we discussing reality, because, if we are, the flows will be choked coming out of the canisters...
    Last edited: Jul 20, 2007
  6. Jul 20, 2007 #5
    i was talking about the state of the containers before heating.
    OP says "I have 2 pressurized canisters, both are 60 litres in size. Both are filled with 120 litres of ideal gas. "
    then the process of heating starts.
    and sorry i didnt understand this line, the first time "Canister B will obviously expand more than Canister A. " i thought that he meant the expansion of gas in higher temp container would be more.
    and i dont think that canister expansion ll have much effect.
    for example, if aluminium canister is used, thermal CoE for which is
    0.000023 per K, volume change for 2000K is 0.138cubic units
  7. Jul 20, 2007 #6


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    Ahhhh...I see what you mean.

    I don't think that the OP meant to consider physical expansion of the canisters but we don't know that right now. The question isn't very specific. I am assuming the only expansion involved is what the gas is trying to do due to the temperature.
  8. Jul 23, 2007 #7
    Ahh, sorry guys, i was not specific enough. In the OP i did not mean that we should consider the expansion of the actual containers, but the expansion of the gas. The first response by Russ was the most accurate and what I was looking for. I will have another question regarding expanding gases soon, so look out for this post. Thanks for all the replies.
  9. Jul 23, 2007 #8
    What does empty mean ?

    It means whith less pressure ( 1 ) or whith less mass of gas ( 2 ) ?

    In case 1, note that for the canister whith high pressure it will take a time to reach the conditions of the canister whith less pressure and then they will be at same pressure. So canister A ( 100 ÂșC ) will empty first.
  10. Jul 24, 2007 #9
    well i didnt get which condition are you referring to alvaros. gas ll be pushed outward because of the pressure differential. canister B has a higher pressure differential.
    apply bernoulli, velocity of rushing gas is directly proportional to pressure differential. both cans have same amount of gas so B ll empty first
  11. Jul 24, 2007 #10
    The condition is pressure.

    Suppose canister A is at 2Kg/cm2 and B at 10 Kg/cm2.
    Yoou open the valves and, after a while, canister B will have 2 Kg/cm2, but then canister A will have less than 2 Gg/cm2, canister A will always be ahead.
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