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Homework Help: Kinetic theory for the molecular condensation flux

  1. Oct 10, 2007 #1
    1. The problem statement, all variables and given/known data
    Start with the kinetic theory formula for the molecular condensation flux, [tex]\Phi_cond[/tex] = 1/4 n_v*c_v, where n_v is the number density of vapor molecules just above a liquid water surface and c_v is the mean speed of the vapor molecules. Derive an expression for calculating the evaporation flux, [tex]\Phi_evap[/tex] in terms of the saturation vapor pressure of water e_s(T) at any given temperature T. The vapor may be treated as an ideal gas.

    2. Relevant equations
    see above

    3. The attempt at a solution

    I know that [tex]\Phi_cond[/tex]=1/4 n_v *c_v = e/ (2[tex]\pi[/tex]m_v*k_b*T)^1/2.
    And that at equilibrium the evaporation flux and condensation flux are equal, but I know you can't say there equal here since it's for any time T. However, I have no idea how to get started. I would think you'd need to do a differential equation such as dn/dt is equal to the flux, but I'm not even sure how to get this set up. If someone could help, it would be greatly appreciated!
  2. jcsd
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