Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35032 Marburg, Germany.
J Chromatogr A. 2011 Nov 11;1218(45):8231-48. doi: 10.1016/j.chroma.2011.09.039. Epub 2011 Sep 21.
Flow and mass transport in bulk and confined chromatographic supports comprising random packings of solid, spherical particles and hexagonal arrays of solid cylinders (regular pillar arrays) are studied over a wide flow velocity range by a numerical analysis scheme, which includes packing generation by a modified Jodrey-Tory algorithm, three-dimensional flow field calculations by the lattice-Boltzmann method, and modeling of advective-diffusive mass transport by a random-walk particle-tracking technique. We demonstrate the impact of the confinement and its cross-sectional geometry (circular, quadratic, semicircular) on transient and asymptotic transverse and longitudinal dispersion in random sphere packings, and also address the influence of protocol-dependent packing disorder and the particle-aspect ratio. Plate height curves are analyzed with the Giddings equation to quantify the transcolumn contribution to eddy dispersion. Confined packings are compared with confined arrays under the condition of identical bed porosity, conduit cross-sectional area, and laterally fully equilibrated geometrical wall and corner effects on dispersion. Fluid dispersion in a regular pillar array is stronger affected by the macroscopic confinement and does not resemble eddy dispersion in random sphere packings, because the regular microstructure cannot function as a mechanical mixer like the random morphology. Giddings' coupling theory fails to preserve the nature of transverse dispersion behind the arrays' plate height curves, which approach a linear velocity-dependence as transverse dispersion becomes velocity-independent. Upon confinement this pseudo-diffusive behavior can outweigh the performance advantage of the regular over the random morphology.
采用一种数值分析方案研究了由固体球形颗粒随机堆积和固体圆柱（规则柱状阵列）六边形阵列组成的整体和受限色谱支撑物中的流动和质量传输，该方案包括通过改进的 Jodrey-Tory 算法生成堆积、通过格子玻尔兹曼方法进行三维流场计算以及通过随机游走粒子跟踪技术对对流扩散质量传输进行建模。我们展示了限制及其横截面几何形状（圆形、方形、半圆形）对随机球堆积中瞬态和渐近横向和纵向弥散的影响，还研究了与协议相关的堆积无序和颗粒纵横比的影响。用 Giddings 方程分析板高曲线，以量化柱间对涡流弥散的贡献。在相同的床层孔隙率、管道横截面积以及横向完全平衡的几何壁和角效应条件下，将受限堆积与受限阵列进行了比较。由于规则微结构不能像随机形态那样充当机械混合器，因此规则柱状阵列中的流体弥散受宏观限制的影响更大，并且不像随机球堆积中的涡流弥散。Giddings 偶联理论不能保持板高曲线后面的横向弥散的性质，因为横向弥散变得与速度无关，板高曲线接近线性速度依赖性。在受限条件下，这种伪扩散行为可能会超过规则形态相对于随机形态的性能优势。
