A narrow residence time distribution (RTD) is desirable in several chemical engineering processes. However, in systems operating at low Reynolds number, axial dispersion can be significant. To lower it, we utilized two mixing approaches: secondary flow achieved with curved geometries and oscillatory variation of the flow rate. We investigated their combined effect on axial dispersion in millifluidic channels with three geometries: straight tube, helically coiled tube (HCT) and coiled flow inverter (CFI). We studied the influence on axial dispersion of two key parameters of pulsating flows: amplitude and frequency of pulsation; in dimensionless form, these are expressed via the amplitude ratio and Strouhal number, respectively. For unsteady flow, we performed numerical simulations to characterise mixing. The results indicate that pulsation enhances radial mixing significantly. Our experimental studies show that axial dispersion is lower in the presence of pulsation, and increasing amplitude and/or frequency has a positive effect. For the same amplitude ratio and Strouhal number, axial dispersion decreases more in the CFIs than in the HCTs. Comparing two extremes, the straight capillary with steady flow (no RTD enhancement) and the CFI with pulsation (lowest axial dispersion achieved in our work), we observed a 10-fold reduction in the axial dispersion number.

在一些化学工程过程中需要窄的停留时间分布 (RTD)。然而，在低雷诺数下运行的系统中，轴向色散可能很重要。为了降低它，我们使用了两种混合方法：通过弯曲的几何形状和流速的振荡变化实现二次流动。我们研究了它们对具有三种几何形状的微流体通道中轴向分散的综合影响：直管、螺旋盘管 (HCT) 和盘绕流逆变器 (CFI)。我们研究了脉动流的两个关键参数对轴向频散的影响：脉动的幅度和频率；在无量纲形式中，它们分别通过振幅比和 Strouhal 数表示。对于不稳定流动，我们进行了数值模拟来表征混合。结果表明脉动显着增强了径向混合。我们的实验研究表明，存在脉动时轴向色散较低，增加振幅和/或频率会产生积极影响。对于相同的振幅比和 Strouhal 数，CFI 中的轴向色散比 HCT 中的减少更多。比较两个极端，具有稳定流动的直毛细管（无 RTD 增强）和具有脉动的 CFI（在我们的工作中实现的最低轴向色散），我们观察到轴向色散数减少了 10 倍。CFI 中的轴向色散比 HCT 中的减少更多。比较两个极端，具有稳定流动的直毛细管（无 RTD 增强）和具有脉动的 CFI（在我们的工作中实现的最低轴向色散），我们观察到轴向色散数减少了 10 倍。CFI 中的轴向色散比 HCT 中的减少更多。比较两个极端，具有稳定流动的直毛细管（无 RTD 增强）和具有脉动的 CFI（在我们的工作中实现的最低轴向色散），我们观察到轴向色散数减少了 10 倍。