Thermal conductivity of polyatomic gases at low density

We present a critical examination of the kinetic theory of dilute polyatomic gases using accurate data for their transport coefficients which have recently become available. Particular attention is concentrated upon the role of inelastic collision processes in the relationship between the thermal conductivity and viscosity of the polyatomic gases H2, D2, N2, CO, CO2, N2O, CH4, C2H4 and C2H6. The thermal conductivity coefficient calculated from the viscosity coefficient with the aid of the most sophisticated kinetic-theory formulae currently available deviates from the experimental data by as much as 15%. These deviations are principally attributed to the neglect of inelastic collision effects which implicitly enter the kinetic-theory formulation and which have traditionally been ignored. This conclusion is supported by calculations of kinetic theory cross-sections based on the infinite-order sudden approximation which retain the full effects of inelastic collisions.