Dahms Rainer N
Combustion Research Facility, Sandia National Laboratories, P.O. Box 969, MS 9051, Livermore, CA 94551, USA.
J Colloid Interface Sci. 2015 May 1;445:48-59. doi: 10.1016/j.jcis.2014.12.069. Epub 2014 Dec 31.
The fidelity of Gradient Theory simulations depends on the accuracy of saturation properties and influence parameters, and require equations of state (EoS) which exhibit a fundamentally consistent behavior in the two-phase regime. Widely applied multi-parameter EoS, however, are generally invalid inside this region. Hence, they may not be fully suitable for application in concert with Gradient Theory despite their ability to accurately predict saturation properties. The commonly assumed temperature-dependence of pure component influence parameters usually restricts their validity to subcritical temperature regimes. This may distort predictions for general multi-component interfaces where temperatures often exceed the critical temperature of vapor phase components. Then, the calculation of influence parameters is not well defined. In this paper, one of the first studies is presented in which Gradient Theory is combined with a next-generation Helmholtz energy EoS which facilitates fundamentally consistent calculations over the entire two-phase regime. Illustrated on pentafluoroethane as an example, reference simulations using this method are performed. They demonstrate the significance of such high-accuracy and fundamentally consistent calculations for the computation of interfacial properties. These reference simulations are compared to corresponding results from cubic PR EoS, widely-applied in combination with Gradient Theory, and mBWR EoS. The analysis reveals that neither of those two methods succeeds to consistently capture the qualitative distribution of obtained key thermodynamic properties in Gradient Theory. Furthermore, a generalized expression of the pure component influence parameter is presented. This development is informed by its fundamental definition based on the direct correlation function of the homogeneous fluid and by presented high-fidelity simulations of interfacial density profiles. The new model preserves the accuracy of previous temperature-dependent expressions, remains well-defined at supercritical temperatures, and is fully suitable for calculations of general multi-component two-phase interfaces.
梯度理论模拟的精度取决于饱和性质和影响参数的准确性，并且需要状态方程（EoS）在两相区域表现出基本一致的行为。然而，广泛应用的多参数状态方程在该区域内通常是无效的。因此，尽管它们能够准确预测饱和性质，但可能不完全适合与梯度理论协同应用。通常假定的纯组分影响参数的温度依赖性通常将其有效性限制在亚临界温度范围。这可能会扭曲对一般多组分界面的预测，因为这些界面的温度通常会超过气相组分的临界温度。那么，影响参数的计算就没有明确的定义。在本文中，首次提出了一项研究，其中将梯度理论与下一代亥姆霍兹能量状态方程相结合，该方程有助于在整个两相区域进行基本一致的计算。以五氟乙烷为例进行说明，使用该方法进行了参考模拟。它们证明了这种高精度和基本一致的计算对于界面性质计算的重要性。将这些参考模拟与立方PR状态方程（广泛与梯度理论结合应用）和mBWR状态方程的相应结果进行了比较。分析表明，这两种方法都无法在梯度理论中一致地捕捉所获得的关键热力学性质的定性分布。此外，还给出了纯组分影响参数的广义表达式。这一发展是基于其基于均相流体的直接相关函数的基本定义以及所呈现的界面密度分布的高保真模拟。新模型保留了先前温度相关表达式的准确性，在超临界温度下仍然定义明确，并且完全适用于一般多组分两相界面的计算。
