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

在此更新建议中，将分析二元系统有机溶剂和超临界CO2之间的热和质量传递机制，分别在混合物临界压力以下和高于临界压力的操作条件下进行。修改后的新实验装置将允许分析乙醇/CO2和丙酮/CO2系统的扩散系数D，在第一个项目期间无法获得扩散系数。在低于混合物临界压力的操作条件下，溶剂和二氧化碳被送入一个可用的高压观察池，这样就形成了两相，最初不处于热力学平衡状态。溶剂从较浓的下层相扩散到较轻的上层相，二氧化碳从较轻的上层相扩散到较浓的下层相，驱动系统（两相）达到热力学平衡。在此期间，通过一维拉曼光谱同时从光相和密相测量了相关组分的部分密度随时间的垂直分布。根据获得的拉曼光谱的校准计算了部分密度。通过将第二菲克斯定律模拟到实验中获得的部分密度分布（它们的时间和空间导数），可以获得每个相中相关组分的扩散系数。对于系统，乙醇/CO2温度分布将在部分密度分布旁边测量，这可以将第一个项目期间估计的汽化和吸附引起的冷却效果与更新期间实验和直接测量的效果进行比较。对于在混合物临界点以上的运行条件下的传热和传质机制的分析，在低于临界压力的压力下，观察单元以前面描述的方式充满流体。当两相体系尚未达到热力学平衡时，将压力增加到混合物临界压力以上，并使用拉曼光谱检测相关组分的部分密度的垂直分布。扩散系数将通过模拟测量的部分密度的时间和空间导数到菲克斯第二定律来计算。对于该系统，乙醇/二氧化碳的温度曲线也将被测量。

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.