Quantification of heat- and masstransfer mechanisms at drops and bubbles in supercritical fluids

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Within this renewal proposal heat and masstransport mechanisms between the binary system organic solvent and supercritical CO2 will be analyzed at operation conditions below and above the mixture critical pressure. A modified new experimental setup will allow the analysis of the diffusivities D for the systems ethanol/CO2 and acetone/CO2, for which the diffusivity could not be made accessible during the first project period. The solvent and the CO2 are fed into an available high pressure view cell at operation conditions below the mixture critical pressure, so that two phases are formed, initially not in thermodynamic equilibrium. The diffusion of the solvent from the dense lower phase into the light upper phase and the diffusion of CO2 from the light upper phase into the dense lower phase drive the system (the two phases) to thermodynamic equilibrium. During this period vertical profiles of the partial densities of the involved components are measured simultaneous from the light and the dense phase as a function of time by means of one-dimensional Raman spectroscopy. The partial densities are computed based on a calibration from the acquired Raman spectra. By modelling second Ficks law to the experimentally achieved partial density profiles (their temporal and spatial derivatives), the diffusivities of the involved components in each phase are made accessible. With respect to the system ethanol/CO2 temperature profiles will be measured next to the partial density profiles, which enables a comparison of the vaporization and sorption caused cooling effects estimated in the first project period and the ones measured during the renewal period experimentally and directly.Regarding the analysis of heat and masstransport mechanisms at operation conditions above the mixture critical point, the view cell is filled with the fluids the way described before at pressures below the critical pressure. When the two-phase system has not yet reached thermodynamic equilibrium the pressure is increased above the mixture critical pressure and the vertical profiles of the partial densities of the involved components are detected using Raman spectroscopy. The diffusivities will be computed by modelling the measured temporal and spatial derivatives of the partial densities to Ficks second law. For the system ethanol/CO2 temperature profiles will be measured, too.