Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35032 Marburg, Germany.
Anal Chem. 2009 Aug 15;81(16):7057-66. doi: 10.1021/ac901187d.
Time and length scales as well as the magnitude of individual contributions to eddy dispersion in chromatographic beds are resolved. We address this issue by a high-resolution numerical analysis of flow and mass transport in computer-generated bulk (unconfined) packings of monosized, nonporous, incompressible, spherical particles and complementary confined cylindrical packings with a cylinder-to-particle diameter ratio of d(c)/d(p) = 20. The transient behavior of longitudinal and transverse dispersion is analyzed and correlated with the spatial scales of heterogeneity in the bulk and confined packings. Simulations were carried out until complete transcolumn equilibration in the confined packings was achieved to facilitate a quantitative study of the geometrical wall effect. Longitudinal plate height data calculated over a wide range of reduced velocities (0.1 < or = nu < or = 500) were fitted to the comprehensive Giddings equation. The determined transition velocities for individual contributions to eddy dispersion were found to be widely disparate. As a consequence, the total effect of eddy dispersion on the plate height curves can be approximated in the practical range of chromatographic operational velocities (5 < or = nu < or = 20) by a composite expression in which only the short-range interchannel contribution retains its coupling characteristics, while transchannel and transcolumn contributions appear as simple mass transfer velocity-proportional terms.
时间和长度尺度以及单个涡流扩散项在色谱床中的贡献大小都得到了明确。我们通过对计算机生成的单尺寸、无孔、不可压缩、球形颗粒的整体（无约束）填充床和补充的约束圆柱填充床中流动和传质的高分辨率数值分析来解决这个问题，其中圆柱与颗粒直径比为 d(c)/d(p) = 20。分析了纵向和横向扩散的瞬态行为，并与整体和约束填充床中不均匀性的空间尺度相关联。模拟进行到约束填充床中的完全跨柱平衡为止，以方便对几何壁效应进行定量研究。在很宽的降速范围（0.1 <或= nu <或= 500）下计算的纵向板高数据被拟合到综合 Giddings 方程中。发现单个涡流扩散项的确定转变速度差异很大。因此，在色谱操作速度的实际范围内（5 <或= nu <或= 20），涡流扩散对板高曲线的总影响可以用一个复合表达式来近似，其中只有短程通道间贡献保留其耦合特性，而跨通道和跨柱贡献则表现为简单的传质速度比例项。
