Axial dispersion of a solute in a flow through packed beds arises from molecular diffusion, velocity variations at the interstitial-pore scale and systematic radial velocity profiles. Currently, there is not a widely accepted procedure for estimating the last contribution. One possible reason is the fact that radial velocity profiles in packed beds are intimately related on the radial porosity profile, which is not a deterministic property, and velocity variations are relatively mild and confined to a region close to the vessel walls. A widespread notion is that only in the zone about a particle radius from the wall is the fluid velocity significantly larger (wall channelling) than in the remaining of the bed core. Based on literature results and effective-model evaluations, the impacts of porosity profiles and related velocity profiles are explored in this manuscript. It is found that the dispersion of a solute can be increased several times in magnitude solely due to the wall channelling when the detailed porosity profile is considered. This can be explained in terms of small velocity differences between a second region (up to around five particle diameters) and the innermost bed region. Guidelines are also discussed for predicting likely levels of dispersion. A further aspect concerns the simplification of the treatment in the wall-zone.

流经填充床的溶质的轴向分散是由分子扩散、间隙孔尺度的速度变化和系统径向速度分布引起的。目前，没有一个被广泛接受的程序来估计最后的贡献。一个可能的原因是填充床中的径向速度分布与径向孔隙度分布密切相关，这不是一个确定性的特性，并且速度变化相对温和并仅限于靠近容器壁的区域。一个普遍的观点是，只有在离壁约一个粒子半径的区域中，流体速度（壁通道）明显大于床芯的其余部分。基于文献结果和有效模型评估，本手稿探讨了孔隙度剖面和相关速度剖面的影响。发现当考虑详细的孔隙度分布时，仅由于壁槽道，溶质的分散量可以增加数倍。这可以通过第二个区域（最多大约五个颗粒直径）和最里面的床区域之间的小速度差异来解释。还讨论了用于预测可能的分散水平的指南。另一方面涉及壁区处理的简化。这可以通过第二个区域（最多大约五个颗粒直径）和最里面的床区域之间的小速度差异来解释。还讨论了用于预测可能的分散水平的指南。另一方面涉及壁区处理的简化。这可以通过第二个区域（最多大约五个颗粒直径）和最里面的床区域之间的小速度差异来解释。还讨论了用于预测可能的分散水平的指南。另一方面涉及壁区处理的简化。