Dense fluids—New aspects and results

Abstract

Dense fluids at elevated and supercritical temperatures find increased interest in science and technology. In this presentation special attention is given to binary mixtures with polar components. Methods and results of experiments with such high pressure-high temperature fluids are described. Far infrared spectra of CHCIF 2 and CHF 3 give indications of the types of molecular motion in the supercritical phases. “Enhancement factors” for the solubility of a solid solute like caffeine in high pressure CO 2 have been determined spectroscopically. The phase diagrams in the pressure-temperature-composition space and critical curves for water combined with nitrogen, oxygen, methane and helium have been measured recently to 2500 bar and 450°C. A “rational” equation of state permits calculation of critical curves and binodal surfaces for such systems. An extended investigation was made with the ternary system water-methane-sodium chloride. Small additions of salt shift critical curves by 100°C and more to higher temperatures. In water-methane mixtures between 400 and 500°C and at 1000 bar “supercritical flames” and “hydrothermal combustion” could be produced with injected oxygen. Binary liquid mixtures of cesium and cesium hydride to elevated hydrogen pressure and to 800°C show the phenomena of continuous transition from metal to ionic fluids. Electric conductance measurements in the whole range of concentrations are presented and discussed.