An equation of state contribution for dipolar and quadrupolar square-well fluids
An equation of state contribution for dipolar and quadrupolar square-well fluids
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DOI：
10.1080/00268970701871015
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发表时间：
2008-01
影响因子：
1.7
通讯作者：
Farzad Alavi;F. Feyzi
中科院分区：
文献类型：
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作者：
Farzad Alavi;F. Feyzi
在pad<s:1>近似的基础上，提出了极方井（方井加点偶极子或点四极子）流体的偶极-四极对残余亥姆霍兹能量的贡献。以方井系统为参照系，利用参照系径向分布函数的展开式，给出了贡献公式。除了平方井势参数外，其贡献仅取决于偶极矩和四极矩。这一项作为扰动加入到方井流体的广义状态方程中。然后将结果与文献中可用的模拟数据进行比较。利用所得到的新方程，可以比现有的多极方井系统微扰理论更准确地预测液-气平衡性质和临界性质。将状态方程应用于实际的偶极（水）和实际的四极（二氧化碳）流体表明，极性贡献极大地改善了饱和度性质的预测。准确预测极方井流体的关键性质仍然是一个挑战。这项工作对发展更好的状态方程是有用的。
A dipolar–quadrupolar contribution to the residual Helmholtz energy for a polar square well (a square well plus either a point dipole or a point quadrupole) fluid is developed based on the Padé approximation. Taking the square well system as reference, the contribution is formulated using an expansion for radial distribution function of the reference system. In addition to square well potential parameters the contribution depends only on dipole and quadrupole moments. This term is added as perturbation to a generalized equation of state for square well fluids. The results are then compared with the available simulation data in the literature. With the new equation obtained, it was possible to predict liquid–vapour equilibrium properties and critical properties of polar square well fluids more accurately than with available perturbation theories for multipolar square well systems. Application of the equation of state to a real dipolar (water) and a real quadrupolar (carbon dioxide) fluid indicated that the polar contribution greatly improved the predictions of saturation properties. Accurate prediction of critical properties for polar square well fluids remains as a challenge. This work can be useful in the development of better equations of state.