【作者】 孟龙；

【导师】 段远源；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2007， 博士

【摘要】 维里系数是流体最基本和最重要的热力学参数之一,与人类的日常生活和生产实践密切相关,也是发展分子热力学理论不可或缺的重要手段。本文理论和实验相结合,研究了流体的维里系数性质的测量、经验关联和理论描述方法。改进了原有的pvT实验系统和实验方案,有效提高了测量精度,减小并修正了非理想因素的影响。采用膨胀定容法高精度测量了纯净物HFC-236fa的pvT性质,建立了维里型状态方程,导出了第二和第三维里系数。测量了HFC-32/HFC-125二元混合物的pvTx性质,导出了混合物第二、第三和交叉维里系数。详细分析了pvT实验系统的测量不确定度及误差传递规律。建立了新的对比态型第二维里系数经验关联式,可广泛适用于各种简单流体、非极性流体、极性流体、缔合流体和量子流体,较好地解决了已有关联式低温区系统负偏差的问题,计算精度高,方便易用。建立了可适用于非极性和极性流体的第三维里系数经验关联式,计算效果好;与第二维里系数关联式相结合,可很好再现中低密度区气相pvT性质。利用新建立的纯净物第二维里系数经验关联式结合经典混合规则,优化了379种混合流体的二元相互作用系数kij。发现了正烷烃类混合物二元相互作用系数的网状分布规律,建立了形式简单而有效的预估方程,仅以碳原子数作为输入参数,可预测含碳原子数高达30的长链烷烃混合物的维里系数。建立了N₂、CO₂、H₂O/正烷烃类、CO/非极性类、碳氟烃类、含量子流体类二元混合物的kij预估方程,用于混合物维里系数计算效果较好。建立了全新的线型分子2CLJDQP势能模型,考虑了偶极作用、四极作用及诱导作用的影响,还考虑了极轴与分子轴不平行的情况;回归了多种线型分子的势能参数;通过改进混合规则,可应用同核线型分子的势能参数直接计算异核线型分子的第二维里系数;扩展该模型可用于线型三原子分子计算;讨论了各长程引力项对第二维里系数的贡献,结果表明本模型引入诱导作用等是十分必要的。更多还原

【Abstract】 The virial coefficients are basic thermophysical properties that can be used to define a wide range of thermodynamic properties and are important in molecular theory. This dissertation presents accurate experimental investigations, empirical correlations and theoretical models of the virial coefficients.The virial coefficient measurements are based on an improved pvT measurement system whose accuracy was significantly enhanced by the minimization of the influence of nonideal factors. The Burnett-isochoric method was used to precisely measure the pvT properties of HFC-236fa. The second and third virial coefficients were then determined along with a truncated virial EOS from the data. The pvTx properties of HFC-32/HFC-125 mixtures were also measured to determine the mixture and cross virial coefficients. The uncertainties of the pvT measurements were carefully analyzed.A new correlation for the second virial coefficients for a variety of fluids was developed based on the corresponding-states principle which can be used for nonpolar, polar, associated and quantum fluids. The convenient correlation corrects the systematic negative errors at subcritical temperatures of existing correlations with enhanced accuracy. A new correlation for the third virial coefficients of various fluids was also developed that is accurate for both nonpolar and polar fluids. With the second virial coefficient correlation, it can provide a very good fit to precise pvT data for low and medium densities.The binary interaction parameters, kij, of 379 nonpolar mixtures were determined by fitting the second cross virial coefficients with the new correlation for pure compounds using classical mixing rules. The kij values for n-alkane/n-alkane binaries have a regular distribution and were successfully correlated with the carbon numbers as the correlating parameters. The correlation was found to perform very well, even for binaries with carbon numbers up to 30. The binary interaction parameters were also successfully correlated for N₂, CO₂, H₂O/n-alkane binaries, CO/nonpolar binaries, fluorocarbon/fluorocarbon binaries and quantum contained binaries.A new theoretical model, the 2CLJDQP potential function, was developed for linear molecules, which takes into account dipole, quadrupole and induction effects as well as the rotation of the dipole out of the molecular axis. The energy parameters were optimized for various types of fluids. With the modified mixing rules, the potential parameters obtained from homonuclear molecules can be used to calculate the second virial coefficients of heteronuclear molecules. The model was also successfully extended to triatomic molecules. Analysis of the contributions to the second virial coefficients of long-range interactions shows that the molecular interactions introduced in the present model, such as, the induction effects, cannot be neglected.更多还原