Abstract The hydrodynamics of gaseous and supercritical CO 2 -ethanol flows in microchannels under elevated pressure (45–90 bar) at 40 °C have been visualized experimentally. The effect of pressure and CO 2 -ethanol mixture composition on the flow regimes developed has been investigated and related to the thermodynamic phase equilibrium diagram. The characteristics of gas-liquid Taylor flow formed at elevated pressure have been analyzed and compared with Taylor flows at ambient conditions. The results of this study show that depending on the pressure and mixture composition, different flow regimes are formed, namely two-phase Taylor flow, dissolving Taylor flow, single-phase jetting-dissolving flow and single-phase supercritical jetting flow. The formation of these flows is explained with respect to the phase equilibrium diagram of CO 2 -ethanol. In the two-phase flow region, Taylor bubble size has been shown to depend on both CO 2 -ethanol mixture composition and operating pressure due to changes in CO 2 mass flow rate and density, respectively. The bubble size formed has shown to increase linearly with U G / U L closely following the well-known bubble formation models for ambient conditions. Due to the non-negligible solubility of CO 2 in ethanol, the Taylor bubble size decreases in the channel until equilibrium is reached. Mass transfer is not easily quantified however due to the mutually soluble nature of CO 2 and ethanol and the dependency of this solubility on pressure.

中文翻译：

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高压下微通道中CO 2 -乙醇流动的流体动力学

摘要 气态和超临界 CO 2 -乙醇在 40 °C 的高压（45-90 bar）下在微通道中流动的流体动力学已通过实验可视化。已经研究了压力和 CO 2 -乙醇混合物组成对流态的影响，并与热力学相平衡图相关。分析了高压下形成的气液泰勒流的特性，并与环境条件下的泰勒流进行了比较。研究结果表明，根据压力和混合物成分的不同，形成了不同的流态，即两相泰勒流、溶解泰勒流、单相喷射-溶解流和单相超临界喷射流。相对于CO 2 -乙醇的相平衡图解释了这些流动的形成。在两相流区域，由于 CO 2 质量流率和密度的变化，泰勒气泡大小已被证明取决于 CO 2 -乙醇混合物的组成和操作压力。形成的气泡尺寸已显示出随着 UG / UL 线性增加，紧随环境条件下众所周知的气泡形成模型。由于 CO 2 在乙醇中不可忽略的溶解度，通道中的泰勒气泡尺寸减小直到达到平衡。然而，由于CO 2 和乙醇的互溶性质以及这种溶解度对压力的依赖性，传质不容易量化。形成的气泡尺寸已显示出随着 UG / UL 线性增加，紧随环境条件下众所周知的气泡形成模型。由于 CO 2 在乙醇中不可忽略的溶解度，通道中的泰勒气泡尺寸减小直到达到平衡。然而，由于CO 2 和乙醇的互溶性质以及这种溶解度对压力的依赖性，传质不容易量化。形成的气泡尺寸已显示出随着 UG / UL 线性增加，紧随环境条件下众所周知的气泡形成模型。由于 CO 2 在乙醇中不可忽略的溶解度，通道中的泰勒气泡尺寸减小直到达到平衡。然而，由于CO 2 和乙醇的互溶性质以及这种溶解度对压力的依赖性，传质不容易量化。