y he transport properties of dilute monatomic gases and monatomic gas mixtures at low to moderate temperatures are now well understood; the rigorous Chapman-Enskog theory provides an entirely adequate description for such gases. Since the theory is derived for molecules
A general expression applying to the steady state has been derived which permits calculation of the increase in thermal conductivity due to chemical reaction in mixtures of gases in chemical equilibrium. In addition to the gas composition, heats of reaction and binary diffusion coefficients among the component gases are required.
In the case of a simple dissociation, the thermal conductivity may be related to the equilibrium heat capacity. This suggests a possible method for estimating heat transfer in various practical systems with dissociating gases.
Approximate calculations for dissociation of diatomic molecules at equilibrium show that the thermal conductivity may be an order of magnitude greater than in nonreacting mixtures. Calculations for the systems 2NO2⇆N2O4 and 6HF⇆(HF)6 are in satisfactory agreement with experiment.
Approximate expressions for the viscosity and thermal conductivity of gas mixtures have been derived from the rigorous kinetic theory formulas. Three levels of approximation are distinguished, with the third approximation rigorous for binary mixtures.
The first approximation for mixture viscosity is found to be very nearly equivalent to empirical expressions known heretofore. The first and second approximations for mixture conductivity have been compared with rigorous calculations for binary mixtures of nonpolar gas pairs; the first approximation has an average error of 2.6% while the second approximation reduces this error to 0.5%.
The second approximation accounts for the thermal conductivity of binary mixtures of polar and nonpolar gases. (It is assumed that the interchange of translational energy is abnormal for the polar-polar interaction.)
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