Page 562 - Bird R.B. Transport phenomena

542 Chapter 17 Diffusivity and the Mechanisms of Mass Transport

17C.2. Mass flux with respect to the solvent velocity.
(a) In a system with N chemical species, choose component N to be the solvent. Then define

j« = P«(v - v )
a
N
to be the mass flux with respect to the solvent velocity. Verify that
)a = )a ~ (P./WJN (17C.2-2)
(b) For a binary system (labeling В as the solvent), show that
)A = (P/PB)U = -( P /PB)®ABVXA (17C.2-3)
2
How does this result simplify for a very dilute solution of Л in solvent B?
17C.3. Determination of Lennard-Jones potential parameters from diffusivity data of a binary gas
mixture.
(a) Use the following data 5 for the system H O-O at 1 atm pressure to determine or and
AB
2
2
S AB /K:
TOO 400 500 600 700 800 900 1000 1100
% AB (cm7s) 0.47 0.69 0.94 1.22 1.52 1.85 2.20 2.58
One way to do this is as follows: (i) Plot the data as \og(T /£b AB) versus log Г on a thin sheet
3/2
of graph paper, (ii) Plot VL J;iAB versus KT/S AB on a separate sheet of graph paper to the same
scale, (iii) Superpose the first plot on the second, and from the scales of the two overlapping
V2
plots, determine the numerical ratios (Т/(кТ/е )) and (fJ /4t )/VLc fjiAB ). (iv) Use these two
AB
АВ
ratios and Eq. 17.3-11 to solve for the two parameters cr and S /K.
AB
AB

5 R. E. Walker and A. A. Westenberg, /. Chem. Phys., 32,436-442 (1960); R. M. Fristrom and
A. A. Westenberg, Flame Structure, McGraw-Hill, New York (1965), p. 265.