相对挥发度平均值的近似计算

Approximation Calculation of the Average Value of Relative Volatility

以Fenske公式求取全回流条件下的最少理论级数时,需要分离组分间的相对挥发度。当相对挥发度非恒定时,需计算平均相对挥发度。在相对挥发度变化不大时一般取塔顶和塔底几何均值,而当相对挥发度变化较大时,需加入第三点的相对挥发度值,合理选取第三点的位置可有效提高计算精度。本文根据相平衡关系的变化趋势,提出了第三点位置的确定方法。该方法理论明确,计算简单,优于简单地取塔中部或进料点。

This paper presents a method to compute the average relative volatility when Fenske Equation is used to obtain the minimum number of stages at total reflux.Besides the relative volatilities at the first and the last stage,another stage between them is required to provide more information about vapor-liquid equilibrium relation.The location of the middle point presented is easy to be determined and usually is not the median or the feed position. Compared to other methods this result is more accurate when the relative volatilities vary greatly.