Transport Coefficients in the Gas Critical Region

The free energy of a system with nonuniform density or composition is assumed to depend quadratically on the density or composition gradient. The contributions of these quadratic terms to the equations of motion are then deduced from a mechanical variational principle. The resultant equations of motion are used to discuss time-dependent correlation functions in the critical region, and to calculate the anomalous shear viscosity η′ and thermal conductivity λ′ of a gas in its critical region. For CO2, λ′ (theory) and λ′ (experiment) are in good agreement. However, η′ (theory) is very small for CO2 [38 (T—Tc)−1/2 μP], and comparison with experiment is inconclusive.