对Wang-Chao活度系数模型的修正

Modification of the Wang-Chao Activity Coefficient Model

将模型流体的微观结构信息引入半经验、半理论的G^E模型中,使其更具理论基础,在理论及工业应用上都很有意义。本文分析了在相平衡计算中得到广泛应用的Wang-Chao模型,认为此模型同时考虑了能量变化和熵变化对G^E的影响,是比较合理的。但它将配位数取为常数6及其局部组成表达式都缺乏充实的理论根据,且与计算机模拟结果不符。本文用Lee和Chao的方阱分子配位数模型修正了W-C模型中的配位数和局部组成式,导出了新的活度系数方程-NWC模型。用NWC模型对包括高度非理想的、有恒沸物存在的24个体系39组等温(等压)汽液平衡数据作了计算。对大部分体系,两参数的(ε_(11)/R,ε_(22)/R)的NWC模型得到了较好的结果。含醇、水等物质的非理想性较强的体系误差较大,对这类体系,增加一个可调参数σ_(22)/σ_(11)后结果略好或相当于W-C原型。本文还对环己烷-乙醇、甲醇-水等体系求取了不同温度下的模型参数ε_(11)/R,ε_(22)/R发现其随温度变化呈良好的线性关系。这种规律性可用于不同温度下的活度系数值及液液平衡、超额焓的推算。此外,还检验了W-C模型将G^E分解为焓、熵贡献的合理性。

By introduction of the simulated results of the square well fluid mixtures, the Wang-Chao activity coefficient model, in which the entropic and enthalpic contributions of mixing have taken into account reasonable was modified. Using the expressions of coordination numbers and local compositions from the molecular simulation, new Wang- Chao equations were developed. Two versions of the new equations, of which one is with two parameters and the other with three, were tested in terms of vapor- liquid equilibrium data of 24 systems with satisfactory accuracy. Moreover, temperature dependence of the parameters and the entropic contribution of the model were discussed.