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Precise determination of LJ parameters and Eucken correction factors for a more accurate modeling of transport properties in gases
Heat and Mass Transfer ( IF 1.7 ) Pub Date : 2020-05-13 , DOI: 10.1007/s00231-020-02871-4
Simon Bechtel , Brian Bayer , Tanja Vidaković-Koch , Artur Wiser , Herbert Vogel , Kai Sundmacher

The kinetic gas theory, in particular the equations of Chapman and Enskog, proved to be good and widely applicable approximations for modeling transport properties like diffusion coefficients, viscosities and thermal conductivities. However, these equations rely on at least the Lennard-Jones parameters and for polar gases also the dipole moment. In the scientific literature, the Lennard-Jones parameters are fitted to only one experimentally determined transport coefficient. This approach leads to good agreement between the Chapman Enskog equations employing the so obtained parameters with the experimental data for this specific transport property. However, utilizing the same parameters for modeling different transport properties oftentimes leads to distinct deviations. In this work, it is shown that the subset of Lennard-Jones parameters with which the Chapman Enskog equations can predict the experimental results with deviations comparable to the experimental uncertainty are not identical for each transport property. Hence, fitting towards one property doesn’t necessarily yield parameters that are suited to describe the other transport properties. In this publication, the Lennard-Jones parameters and a temperature dependent Eucken correction factor, leading to a significantly higher accuracy than the classical Eucken correction and also its modification by Hirschfelder, are therefore fitted towards all three transport properties simultaneously for seven exemplary gases. This approach leads to a significantly better agreement with experimental data for the three transport properties than the classical approach that relies on fitting to one single transport property and can be utilized to determine accurate sets of Lennard-Jones parameters and Eucken correction factors for any gas species. It provides a computationally inexpensive and practical method for the precise calculation of transport properties over a wide range of temperatures relevant for processes in the chemical industry.



中文翻译:

精确确定LJ参数和Eucken校正因子,以更准确地模拟气体中的传输特性

动力学气体理论,特别是Chapman和Enskog方程,被证明是良好的近似方法,可用于模拟传输特性,如扩散系数,粘度和热导率。但是,这些方程至少依赖于Lennard-Jones参数,对于极性气体,也取决于偶极矩。在科学文献中,Lennard-Jones参数仅适用于一个实验确定的传输系数。这种方法导致使用这样获得的参数的查普曼Enskog方程与该特定传输特性的实验数据之间具有良好的一致性。然而,利用相同的参数来建模不同的传输特性通常会导致明显的偏差。在这项工作中 结果表明,Chapman Enskog方程可用来预测实验结果的Lennard-Jones参数子集对于每种输运性质而言都不相同。因此,对一个属性进行拟合并不一定会产生适合描述其他传输属性的参数。因此,在该出版物中,Lennard-Jones参数和与温度有关的Eucken校正因子,比经典的Eucken校正具有显着更高的精度,并且通过Hirschfelder对其进行了修改,因此可以同时针对所有7种示例性气体拟合所有三种传输特性。与经典方法(依赖于拟合单个运输属性并可以用于确定任何气体种类的准确Lennard-Jones参数和Eucken校正因子)相比,该方法与三种运输特性的实验数据之间的一致性更好。 。它提供了一种计算上不昂贵且实用的方法,用于精确计算与化工行业相关的各种温度范围内的传输性能。

更新日期:2020-05-13
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