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Homework Help: Speed of Hydrogen combustion out of a tube?

  1. Jul 3, 2016 #1
    • Please post this type of questions in the HW section using the template.
    Hello, I was curious about how to calculate how fast the escape velocity of hydrogen out of a tube/cylinder would be. Once end of the cylinder is closed, the other is open, obviously.

    Assume the cylinder is full of hydrogen at 1 atm. My thought is that you could use PV=NRT to calculate the volume of the hydrogen once combusted and then imagine a sphere that had that equivalent volume. Online i found that the max flame speed of hydrogen is 3.06 m/s. I think you could start from the center of the sphere and calculate how long it would take to fill that volume if you went out radially at that speed(radius/3.06 m/s). Take the volume and divide it by the time to get the rate.

    Once you have that rate, you could take the rate of the combustion (Vol/sec) and divide that by the volume of the cylinder to get the multiple. For example: if the rate of combustion is 1000L/sec and the cylinder is 1 L, then the gas will expand to 1000x the volume of the cylinder in 1 second. By multiplying the length * the multiple(1000) and dividing by 1 second, that would give a decent approximation for the escape velocity of the gas coming out of the tube. Them multiplying that by the mass/sec (flow rate) gives you the thrust.

    Does this seem reasonable? Or is there an equation i can use for this.
  2. jcsd
  3. Jul 3, 2016 #2
    This is not for school, just my own curiosity.
  4. Jul 3, 2016 #3


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    Staff: Mentor

    I am afraid you are mixing completely irrelevant and independent phenomena and the calculation you did doesn't make any sense.
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