Transport properties of fluid mixtures in the critical region

Abstract

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 the thermal conductivity, the viscosity, the mutual diffusivity, and the thermal-diffusion coefficients of binary mixtures. The resulting expressions not only are valid in the asymptotic critical region but also describe the crossover to regular behavior far away from a critical point. The crossover functions depend on the thermodynamic properties of the mixtures, background values of all transport coefficients, and two concentration-dependent cutoff wave numbers. We compare the proposed crossover model with experimental thermal-conductivity data for mixtures of carbon dioxide and ethane in the critical region and find good agreement between theory and experiment.

Thermodiffusion in the Critical Region

“…It was not until Sakonidou et al [37,53] performed thermal conductivity measurements near the vapor-liquid critical point of a methane-ethane mixture, that the limiting finite behavior of the thermal conductivity near a plait point was observed experimentally. These data also confirmed the predicted crossover [23,25] from the pure-fluid like behavior at some distance from the critical point to the mixture-like behavior, λ T ∼ const., very close to the critical point. In Fig.…”

“…Mode-coupling theories [11][12][13], on the other hand, originated from the idea of Fixman [14] that the critical enhancements of the transport coefficients are the result of non-linear coupling between the hydrodynamic modes of the system. Dynamic renormalization-group and mode-coupling theories, as well as the related decoupled-mode theory of Perl and Ferrell [15,16], have recently been extended to describe the crossover behavior of transport properties of fluids and their mixtures [17][18][19][20][21][22][23][24][25][26][27][28].…”

Thermophysical properties of supercritical fluids and fluid mixtures. Final technical report, December 15, 1988--December 14, 1994

“…We have also developed equations to account for the crossover behavior of the thermal conductivity [2, 30,38].…”

“…Most recently we have also succeeded in extendug the theory of the global critical behavior of the transport properties to binary mixtures [30,35]. In parallel to the development of this theory, we have measured the thermal conductivity of mixtures of carbon dioxide and ethane with a parallel-plate apparatus especially suited for the measurement of the thermal conductivity of fluids in the critical region [ 1 1, 16,19].…”

“…In parallel to the development of this theory, we have measured the thermal conductivity of mixtures of carbon dioxide and ethane with a parallel-plate apparatus especially suited for the measurement of the thermal conductivity of fluids in the critical region [ 1 1, 16,19]. With the new crossover equations for the transport properties of mixtures we have been able to obtain a good description of these experimental thermal conductivities for the carbon-dioxide + ethane system [30]. Moreover, from these equations we are also able to predict the behavior of other transport properties of this mixture, like the thermaldiffusion ratio [30].…”