To advance the thermodynamic models needed for many industrial processes, accurate measurements of fluid-phase behavior are essential. Therefore, we present a newly designed microwave re-entrant cavity apparatus to deliver improved phase-behavior measurements of pure and multicomponent fluids. The re-entrant geometry has spatially distinct resonant modes, which are used to determine the dielectric permittivity of the liquid and vapor phase and the liquid volume fraction (Λ). The first mode (f_vac ≈ 320 MHz) is sensitive to small liquid volumes, the second (1.86 GHz) is sensitive to small vapor volumes, and the third (6.57 GHz) is sensitive to the interface location. At equilibrium, a system of three equations, one for each mode, allows for the dielectric permittivity of each phase and Λ to be determined from the measured resonant frequencies. The cavity’s suitability for solving this inverse problem was explored using finite element analysis and experiments with pure propane and pentane. A primary limitation of the method was the dependence of the mode-shape functions (G_n) on phase permittivities, which become measurable for high-frequency modes. We propose a solution to account for this dependence using finite element simulations that map the G_n surface as a function of Λ and the ratio of phase dielectric permittivities.

中文翻译：

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使用先进的微波凹腔对流体行为进行表征

为了推进许多工业过程所需的热力学模型，准确测量液相行为至关重要。因此，我们提出了一种新设计的微波凹腔装置，以提供纯净和多组分流体的改进的相行为测量。凹入几何形状具有空间上不同的共振模式，该共振模式用于确定液相和气相的介电常数以及液体体积分数（Λ）。第一模式（˚F _VAC≈320 MHz）对较小的液体体积敏感，第二个（1.86 GHz）对较小的蒸气体积敏感，而第三个（6.57 GHz）对界面位置敏感。在平衡状态下，由三个方程式组成的系统，每个方程式一个，允许根据测量的谐振频率确定每个相位的介电常数和。使用有限元分析和纯丙烷和戊烷的实验，探索了腔体解决此反问题的适用性。该方法的主要局限在于模式形状函数（G _n）对相位介电常数的依赖性，而相位介电常数对于高频模式是可以测量的。我们提出了一种解决方案，使用映射G _n的有限元模拟解决了这种依赖性 表面与Λ和相介电常数之比的函数。