传质系数与浓度的关系

RELATIONSHIP BETWEEN MASS TRANSFER COEFFICIENT AND CONCENTRATION

在含 6块塔板的板式塔中选择 2个非理想性较大的二元物系进行全回流蒸馏传质实验 ,同时从描述多组分扩散过程的普遍化方程———Maxwell-Stefan(MS)方程出发建立一个求算传质系数的数学模型 .数据处理和计算的结果表明 ,传质系数不仅与该塔板的浓度有关 ,还与相邻塔板的浓度有关 .对于非理想程度大的醇水物系 ,在不同浓度下的传质系数最大值与最小值相差可达约 1个数量级 .因此 ,对于非理想物系 ,在设计计算中将传质系数当作常数的处理将会产生较大误差 .

Mass transfer coefficient is an important parameter in the calculation and design of mass transfer processes. Many variables affect the value of mass transfer coefficient. Among which, the effect of concentration has not yet been paid due attention. In an experimental column containing 6 trays, two non-ideal binary mixtures are distilled under total reflux to study the relationship between mass transfer coefficient and concentration. Based on the experimental data and Maxwell-Stefan equation, a mathematical model for calculating mass transfer coefficient is presented. The results show that mass transfer coefficient depends not only on the concentration of the vapor and liquid on the tray, but also on the concentration of the vapor and liquid on the neighboring tray. For highly non-ideal alcohol-water systems, the difference between the maximum and the minimum values of mass transfer coefficients is about an order of magnitude, therefore, the assumption of constant mass transfer coefficient in common design practice for non-ideal systems may lead to considerable error.