Diffusivities of an Equimolar Methane–Propane Mixture Across the Two-Phase Region by Dynamic Light Scattering
Diffusivities of an Equimolar Methane–Propane Mixture Across the Two-Phase Region by Dynamic Light Scattering
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DOI：
10.1007/s10765-020-02680-1
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发表时间：
2020-05
影响因子：
2.2
通讯作者：
M. Piszko;C. Giraudet;A. Fröba
中科院分区：
文献类型：
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作者：
M. Piszko;C. Giraudet;A. Fröba
本论文研究了动态光散射（DLS）实验中等摩尔甲烷-丙烷混合物两相区域扩散率的可及性。在包括气体、液体、超临界和两相区在内的 125 个不同的热力学状态下进行了外差 DLS 实验和瑞利比的理论计算。目前的测量证明，对于对应于大于临界密度 1.15 倍的密度的温度和压力，可以在液态和饱和液相中同时确定两个扩散率。根据本工作中检测到的信号的严格分配，慢扩散率和快扩散率可能与菲克扩散率和热扩散率相关。对于所有其他热力学状态，通过实验获得单一流体力学模式或信号。借助理论瑞利比以及扩散率随温度和压力变化的一般行为，信号被确定与超临界状态下的菲克扩散率以及气态和饱和蒸气相的混合扩散率有关。结合混合物相图压力-温度投影中某些路径的扩散行为对结果进行了讨论。
The present contribution examines the accessibility of diffusivities across the two-phase region of an equimolar methane–propane mixture for dynamic light scattering (DLS) experiments. Heterodyne DLS experiments and theoretical calculations of the Rayleigh ratio were performed at 125 different thermodynamic states including the gas, liquid, supercritical, and the two-phase region. The present measurements document that two diffusivities can be determined simultaneously in the liquid state and saturated liquid phase for temperatures and pressures which correspond to densities larger than 1.15 times the critical density. Based on a rigorous assignment of the signals detected in this work, the slow and fast diffusivities could be associated with the Fick and thermal diffusivities. For all other thermodynamic states, a single hydrodynamic mode or signal was obtained experimentally. With the help of theoretical Rayleigh ratios as well as from the general behavior of the diffusivities as a function of temperature and pressure, the signals were identified to be related to the Fick diffusivity in the supercritical state and to a mixed diffusivity in the gas state and the saturated vapor phase. The results are discussed in connection with the behavior of the diffusivities along certain paths in the pressure–temperature projection of the phase diagram of the mixture.