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Diffusivities of an Equimolar Methane–Propane Mixture Across the Two-Phase Region by Dynamic Light Scattering
International Journal of Thermophysics ( IF 2.2 ) Pub Date : 2020-05-23 , DOI: 10.1007/s10765-020-02680-1
Maximilian Piszko , Cédric Giraudet , Andreas P. Fröba

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.

中文翻译:

等摩尔甲烷-丙烷混合物通过动态光散射在两相区域的扩散率

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的扩散率的可及性。外差 DLS 实验和瑞利比的理论计算在 125 种不同的热力学状态下进行,包括气体、液体、超临界和两相区域。本测量证明,对于对应于大于临界密度 1.15 倍的密度的温度和压力,可以同时确定液态和饱和液相中的两种扩散系数。根据这项工作中检测到​​的信号的严格分配,慢速和快速扩散率可能与 Fick 和热扩散率有关。对于所有其他热力学状态,通过实验获得了单一的流体动力学模式或信号。借助理论瑞利比以及作为温度和压力函数的扩散率的一般行为,确定信号与超临界状态下的 Fick 扩散率和气态下的混合扩散率有关,并且饱和汽相。结合在混合物相图的压力-温度投影中沿某些路径的扩散行为来讨论结果。确定这些信号与超临界状态下的 Fick 扩散率以及气态和饱和汽相的混合扩散率有关。结合在混合物相图的压力-温度投影中沿某些路径的扩散行为来讨论结果。这些信号被确定为与超临界状态下的 Fick 扩散系数以及气态和饱和蒸气相的混合扩散系数有关。结合在混合物相图的压力-温度投影中沿某些路径的扩散行为来讨论结果。
更新日期:2020-05-23
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