Transport Properties Of Fluid Mixtures Research Articles

Prediction of thermodynamic and transport properties in the one-phase region of methane + n-hexane mixtures near their critical end points

A recently developed generalized isomorphism approach enables us to account for the critical behavior of thermodynamic and transport properties of fluid mixtures that exhibit continuous crossover from vapor-liquid critical phenomena to liquid-liquid critical phenomena. As an application we show here how the method can be used to predict thermodynamic and transport properties of methane + n-hexane mixtures in the one-phase region near their critical end points based on available liquid-liquid-vapor equilibria data for the mixtures and on the properties of the pure components.

The transport properties of fluid mixtures near the vapor–liquid critical line

We apply the mode-coupling theory for the dynamics of critical fluctuations to binary fluid mixtures near the vapor–liquid critical line and derive a set of coupled equations for the mode-coupling contributions to the diffusion coefficients of the relevant hydrodynamic modes. An approximate solution of the mode-coupling integrals yields representative equations for the effects of the critical fluctuations on the thermal conductivity, the viscosity, the mutual diffusivity and the thermal-diffusion coefficient, which are valid not only in the asymptotic critical region but also describe the crossover to regular behavior far away from the critical line. The ‘‘crossover’’ functions depend on the thermodynamic properties of the mixtures, background values of all the 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.

A general isomorphism approach to thermodynamic and transport properties of binary fluid mixtures near critical points

A general isomorphism approach to critical phenomena in binary fluid mixtures that may exhibit complex critical-line behavior is developed by relating the two relevant scaling fields to linear combinations of three physical field variables. These physical field variables are related to the temperature and chemical potentials of the two components. The proposed approach includes crossover from vapor-liquid critical behavior to liquid-liquid critical behavior and incorporates also the critical behavior near other special points on critical loci. It is shown that the key factor which determines the apparent behavior of the thermodynamic and transport properties of near-critical mixtures is the shape of the critical locus. The number of system-dependent coefficients that determine the asymptotic critical behavior is elucidated. The choice of zero-points of entropy and energy in binary mixtures is also discussed. The approach provides a powerful tool for predicting thermodynamic and transport properties of fluid mixtures in the critical region.

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 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.

特集 混合流体の熱物性 混合流体の輸送性質 粘性率と熱伝導率

特集 混合流体の熱物性 混合流体の輸送性質 粘性率と熱伝導率