THERMOGRAVITATIONAL SEPARATION AND THE THERMAL-DIFFUSION FACTOR NEAR CRITICAL-POINTS IN BINARY-LIQUID MIXTURES

The thermogravitational separation for each of the binary liquid syste ms nitrobenzene + n-hexane and isobutyric acid + water, as a function of composition, was measured at temperatures above and near to their c ritical conditions. The first system, in which the component densities are very different, presents large separations near the critical comp osition. In contrast, in the second one, with similar densities of the pure components, no separation is observed. The extension to high Sor et numbers of our previously developed thermogravitational theory, whi ch takes into account the effect of the bouyancy-driven convection ind uced by the density composition dependence allows us to obtain values of thermal diffusion factors of binary liquid mixtures in the vicinity of consolute points from separation measurements.