TRANSPORT-PROPERTIES OF FLUID MIXTURES IN THE CRITICAL REGION

Transport properties of fluid mixtures exhibit anomalous behavior near the vapor-liquid critical line. These anomalies are a result of long- range fluctuations in the system in the vicinity of a critical point. We use mode-coupling theory to describe the critical enhancements of t he thermal conductivity, the viscosity, the mutual diffusivity, and th e thermal-diffusion coefficients of binary mixtures. The resulting exp ressions not only are valid in the asymptotic critical region but also describe the crossover to regular behavior far away from a critical p oint. The crossover functions depend on the thermodynamic properties o f the mixtures, background values of all transport coefficients, and t wo concentration-dependent cutoff wave numbers. We compare the propose d crossover model with experimental thermal-conductivity data for mixt ures of carbon dioxide and ethane in the critical region and find good agreement between theory and experiment.