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Mean Free Path of Gases with Bulk Velocities

  1. Oct 10, 2011 #1
    Hello all,

    I'm modeling a situation in which a gas moves through a pressure gradient established by a quartz frit with 40-100 μm sized pores. What I'm interested in finding out is how the mean free path of the gas changes after it exits the frit region, if at all.

    I think that the mean free path of the gas should increase. I say this based off of a limiting case in which the bulk velocity of the gas (x direction) becomes far greater than the average y and z components of the velocity meaning in a given time interval, the particles travel much farther along x than along y and z, making the mean free path infinite.

    What I think is happening here is that the maxwell distributions (for speeds) in the y and z direction are untouched but that the maxwell distribution in the x component gets shifted. What I think this means is that for the y and z directions, the distances traveled before collisions remain the same but in the x direction the distance that the molecules travel increases by a factor of v_exit/v_enter, meaning the total mfp changes by a factor of norm(<v_exit, v_y, v_z>)/norm (<v_enter, v_y, v_z>)

    Could someone help me understand this. It would be greatly appreciated
  2. jcsd
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