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2.2. DIFFUSION 45
Gas Pair σ 12 ( A) o ε 12 /k (K) T (K) [D 12 ] 1
(cm 2 s −1 )
Calculated Experimental
N 2 -H 2 3.325 55.2
273.2
288.2
293.2
0.656
0.718
0.739
0.674
0.743
0.760
N 2-O 2 3.557 102
273.2 0.175 0.181
293.2 0.199 0.220
N 2 -CO 3.636 100 273.2 0.174 0.192
N 2-CO 2 3.839 132
273.2
288.2
293.2
298.2
0.130
0.143
0.147
0.152
0.144
0.158
0.160
0.165
N 2 -C 2 H 4 3.957 137 298.2 0.156 0.163
N 2 -C 2 H 6 4.050 145 298.2 0.144 0.148
N 2-nC 4H 10 4.339 194 298.2 0.0986 0.0960
N 2-iso-C 4H 10 4.511 169 298.2 0.0970 0.0908
H 2 -O 2 3.201 61.4 273.2 0.689 0.697
H 2 -CO 3.279 60.6 273.2 0.661 0.651
273.2 0.544 0.550
H 2-CO 2 3.482 79.5
288.2 0.597 0.619
293.2 0.616 0.600
298.2 0.634 0.646
H 2 -N 2 O 3.424 85.6 273.2 0.552 0.535
H 2 -SF 6 3.922 89.1 298.2 0.473 0.420
H 2-CH 4 3.425 67.4
273.2 0.607 0.625
298.2 0.705 0.726
H 2 -C 2 H 4 3.600 82.6 298.2 0.595 0.602
H 2 -C 2 H 6 3.693 87.5 298.2 0.556 0.537
CO-O 2 3.512 112 273.2 0.175 0.185
CO 2 -O 2 3.715 147
273.2 0.128 0.139
293.2 0.146 0.160
CO 2 -CO 3.793 145 273.2 0.128 0.137
CO 2 -N 2 O 3.938 204 273.2 0.092 0.096
CO 2-CH 4 3.939 161 273.2 0.138 0.153
Table 2.2: Comparison of diffusion coefficients for some binary mixtures. Theoretical values
correspond to Lennard-Jones interaction potential.
Approximation of order j can be expressed in the form 13
[D 12 ] j
= [D 12 ] 1
f j D 12
. (2.23)
For example, for the second approximation, fD 2 12
depends on the molar masses
of the species, on their mass fractions, viscosity coefficients and temperature of the
mixture. Its value is always close to one. For the Lennard-Jones potential, for instance,
it ranges from 1 to 1.03.
13 See Ref. [2], p. 539.