Giraudet Cédric, Klein Tobias, Zhao Guanjia, Rausch Michael H, Koller Thomas M, Fröba Andreas P
Institute of Advanced Optical Technologies - Thermophysical Properties (AOT-TP), Department of Chemical and Biological Engineering (CBI) and Erlangen Graduate School in Advanced Optical Technologies (SAOT) , Friedrich-Alexander-University Erlangen-Nürnberg (FAU) , Paul-Gordan-Straße 6 , 91052 Erlangen , Germany.
Thermal Engineering, College of Electrical and Power Engineering , Taiyuan University of Technology , Taiyuan , Shanxi CN 030024 , China.
J Phys Chem B. 2018 Mar 29;122(12):3163-3175. doi: 10.1021/acs.jpcb.8b00733. Epub 2018 Mar 20.
In the present study, dynamic light scattering (DLS) experiments and molecular dynamics (MD) simulations were used for the investigation of the molecular diffusion in binary mixtures of liquids with dissolved gases at macroscopic thermodynamic equilibrium. Model systems based on the n-alkane n-hexane or n-decane with dissolved hydrogen, helium, nitrogen, or carbon monoxide were studied at temperatures between 303 and 423 K and at gas mole fractions below 0.06. With DLS, the relaxation behavior of microscopic equilibrium fluctuations in concentration and temperature is analyzed to determine simultaneously mutual and thermal diffusivity in an absolute way. The present measurements document that even for mole gas fractions of 0.007 and Lewis numbers close to 1, reliable mutual diffusivities with an average expanded uncertainty ( k = 2) of 13% can be obtained. By use of suitable molecular models for the mixture components, the self-diffusion coefficient of the gases was determined by MD simulations with an averaged expanded uncertainty ( k = 2) of 7%. The DLS experiments showed that the thermal diffusivity of the studied systems is not affected by the dissolved gas and agrees with the reference data for the pure n-alkanes. In agreement with theory, mutual diffusivities and self-diffusivities were found to be equal mostly within combined uncertainties at conditions approaching infinite dilution of the gas. Our DLS and MD results, representing the first available data for the present systems, reveal distinctly larger mass diffusivities for mixtures containing hydrogen or helium compared to mixtures containing nitrogen or carbon monoxide. On the basis of the broad range of mass diffusivities of the studied gas-liquid systems covering about 2 orders of magnitude from about 10 to 10 m·s, effects of the solvent and solute properties on the temperature-dependent mass diffusivities are discussed. This contributed to the development of a simple semiempirical correlation for the mass diffusivity of the studied gases dissolved in n-alkanes of varying chain length at infinite dilution as a function of temperature. The generalized expression requiring only information on the kinematic viscosity and molar mass of the pure solvent as well as the molar mass and acentric factor of the solute represents the database from this work and further literature with an absolute average deviation of about 11%.
在本研究中，动态光散射（DLS）实验和分子动力学（MD）模拟被用于研究在宏观热力学平衡下，溶解有气体的液体二元混合物中的分子扩散。研究了基于正构烷烃正己烷或正癸烷与溶解的氢气、氦气、氮气或一氧化碳的模型体系，温度范围为303至423 K，气体摩尔分数低于0.06。通过DLS，分析浓度和温度微观平衡涨落的弛豫行为，以绝对方式同时确定互扩散系数和热扩散系数。目前的测量结果表明，即使对于摩尔气体分数为0.007且路易斯数接近1的情况，也能获得平均扩展不确定度（k = 2）为13%的可靠互扩散系数。通过使用适合混合物组分的分子模型，通过MD模拟确定了气体的自扩散系数，平均扩展不确定度（k = 2）为7%。DLS实验表明，所研究体系的热扩散系数不受溶解气体的影响，与纯正构烷烃的参考数据一致。与理论一致，在接近气体无限稀释的条件下，互扩散系数和自扩散系数在组合不确定度范围内大多相等。我们的DLS和MD结果是目前这些体系的首批可用数据，表明与含有氮气或一氧化碳的混合物相比，含有氢气或氦气的混合物具有明显更大的质量扩散系数。基于所研究的气液体系广泛的质量扩散系数范围，其涵盖了从约10到10 m·s的约2个数量级，讨论了溶剂和溶质性质对温度依赖性质量扩散系数的影响。这有助于建立一个简单的半经验关联式，用于描述在无限稀释下，所研究的溶解在不同链长正构烷烃中的气体的质量扩散系数与温度的函数关系。该广义表达式仅需要关于纯溶剂的运动粘度和摩尔质量以及溶质的摩尔质量和偏心因子的信息，代表了这项工作以及更多文献的数据库，绝对平均偏差约为11%。
