Theoretical and experimental comparison of the Soret coefficient for water-methanol and water-ethanol binary mixtures

Abstract

In multicomponent mixtures, a much richer variety of phenomena can occur than in simple (single-component) fluids. Natural convection in single-component fluids is due to buoyancy forces caused by temperature gradients. In multicomponent mixtures, buoyancy forces may also be caused by concentration gradients. Because natural convection, molecular diffusion, and thermal conduction have different relaxation time scales, a wide variety of resulting convective motions and heat and mass distributions might occur. In some fluid mixtures such as water-ethanol system, for instance, ethanol diffuses much more slowly than heat, and because of this difference in time scales oscillatory convection might occur. In a multicomponent mixture, the total molar flux consists of two parts: the convective molar flux and the diffusive molar flux (resulting from the difference between the component velocity and the bulk velocity). The diffusion molar flux of a component depends, not only on its own mole fraction gradient (Fickian diffusion), but also on the gradient of all the components present in the mixture (cross-molecular diffusion). The diffusion flux depends also on the pressure gradient (pressure diffusion; the so-called gravitational effect) and temperature gradient (thermal diffusion; the so-called Soret effect). Firoozabadi's thermal diffusion model was applied to calculate the Soret coefficient, as well as the thermal diffusion coefficient and molecular diffusion coefficient for methanol-water and ethanol-water mixtures at 310.65 K temperature and 1 bar pressure with 10% water mass fraction. The results were compared with experimental data (J.K. Platten, in Proceedings of the 5th International Meeting on Thermodiffusion (IMT5), Lyngby, Aug. 2002, Philos. Mag. 83, Nos. 17-18 (2003)), as well as theoretical predictions with other models. A better agreement with the experimental data using the Firoozabadi model was achieved.

Thermophoretic Motion of Water Nanodroplets Confined inside Carbon Nanotubes

“…This value is 3 orders of magnitude larger than the coefficients reported by Platten et al 12 and Saghir et al 44 for mixtures of water-methanol and by Reith and MullerPlathe 45 of binary Lennard-Jones liquids. In order to evaluate the influence of the wetting of the water-carbon interface on the thermophoretic motion of the nanodroplet, we vary the Lennard-Jones parameter ε co , from the reference value of 0.3920 kJ/mol to 0.5643 and 0.2508 kJ/mol, which correspond to strongly hydrophilic and strongly hydrophobic interfaces, respectively.…”

Simulation of Ludwig–Soret effect of a water–ethanol mixture in a cavity filled with aluminum oxide powder under high pressure

“…[ [6,19]. Generally, when water content is less then 60% in the mixture, the theoretical prediction of the Firoozabadi model is closer to the experimental data.…”

“…Generally, when water content is less then 60% in the mixture, the theoretical prediction of the Firoozabadi model is closer to the experimental data. For the water-ethanol mixtures with a 90 and 50% mass fraction of ethanol at 37.5 and 22.5 • C, respectively, the experiment data at atmospheric pressure [6,12] was used to compare with the predictions of the Firoozabadi model. The thermal diffusion flux equation is given below in the experiment:…”

“…Based on the non-equilibrium thermodynamics theory of De Groot [3], many models were proposed to predict the thermal diffusion coefficient as well as the Soret coefficient based on properties of components and properties of mixtures, such as the Haase model [4] and the Firoozabadi model [5]. In other literature, the Firoozabadi model was shown to have a stronger performance in predicting the thermal diffusion coefficient, as well as the Soret coefficient, among available models in both hydrocarbon mixtures [5] and water-alcohol mixtures [6].…”

Theoretical analysis and comparison with experimentation of the molecular and thermal diffusion coefficients for a ternary hydrocarbon mixture

“…Saghir et al [10] compared the results obtained using the Firoozabadi model, with the CPA equation of state, to the experimental data obtained by Platten [11]. Two polar mixtures, methanol-water and ethanol-water, with 0.835mole fraction of methanol and 0.779-mole fraction of ethanol, respectively, were utilized.…”