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Homework Help: Deriving the diffusion constant D

  1. Mar 27, 2016 #1
    1. The problem statement, all variables and given/known data
    Prove that the diffusion constant D of an ideal gas can be expressed as D=1/3λv(v bar) where λ is the mean free pass of the gas molecule. And v bar is the average speed of the gas molecules obtained from the kinetic theory of gases.(Use the picture to setup the net flux change of gas molecules flowing from a negative to positive z direction.)

    2. Relevant equations
    Use the Taylor expansion of the form
    f (x) = a0f(0)+ a1(df/dx)(x=0)x +....+ an(d^nf/dx^n)(x=0)x^n
    for calculating the concentration c(z) on z axis at z = ±λ with the initial condition c(z=0)=c0 . When doing so, use the first two terms only of the expansion and use a1 = 2/3 for this particular system. You may need to use the molecular flux Φ (i.e. # of molecules crossing a unit area per a unit time) of the gas.

    3. The attempt at a solution
    I've tried to solve as deriving the the coefficient of viscosity, but I couldn't. ;(

    Attached Files:

  2. jcsd
  3. Apr 1, 2016 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
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