Vrije Universiteit Brussel, Department of Chemical Engineering, Pleinlaan 2, 1050 Brussels, Belgium.
J Chromatogr A. 2012 Mar 2;1227:194-202. doi: 10.1016/j.chroma.2012.01.007. Epub 2012 Jan 11.
Numerical calculations of the mobile zone mass transfer rate in a variety of ordered 2D and 3D structures are presented. These calculations are in line with earlier theoretical and experimental findings made in the field of chemical engineering and suggest that the Sherwood-number (Sh(m)) appearing in the mobile phase mass transfer term of the general plate height expression of liquid chromatography is not correctly predicted by the Wilson-Geankoplis--or the Kataoka--or the penetration model expression that have been used up to now to in the field of LC, and that at least more research is needed before these expressions can be continued to be used with confidence. The aforementioned expressions were obtained by neglecting the effect of axial dispersion on the mass transfer process, and it seems that they therefore underestimate the true Sh(m)-number by a factor of 2-5 around the minimum of the van Deemter-curve. New correlations describing the variation of the Sh(m)-coefficient as a function of the reduced velocity for a number of other packing geometries (tetrahedral monolith, 2D pillar array) are proposed. These correlations are in agreement with earlier theoretical and experimental studies showing that at low velocities the local-driving force-based Sh(m)-value is of the order of 10-20 in a packed bed column with an external porosity on the order of 35-40%.
呈现了在各种有序的 2D 和 3D 结构中移动区域传质速率的数值计算。这些计算与化学工程领域的早期理论和实验结果一致，表明在液相色谱的一般板高表达式中出现在移动相传质项中的 Sherwood 数（Sh(m)）不能被迄今为止在 LC 领域中使用的 Wilson-Geankoplis-或 Kataoka-或穿透模型表达式正确预测，并且在这些表达式能够被继续自信地使用之前，至少需要更多的研究。上述表达式是通过忽略轴向扩散对传质过程的影响而获得的，因此它们似乎低估了真实的 Sh(m)-数，低估幅度约为 van Deemter 曲线最小值处的 2-5 倍。提出了新的关联式，用于描述在许多其他填充几何形状（四面体整体、2D 柱阵列）下 Sh(m)-系数随减小速度的变化。这些关联式与早期的理论和实验研究一致，表明在低流速下，在外部孔隙度约为 35-40%的填充床柱中，基于局部驱动力的 Sh(m)-值约为 10-20。
