Jacob Jack D C, Krishnamoorti Ramanan, Conrad Jacinta C
Department of Chemical & Biomolecular Engineering, University of Houston, Houston, Texas 77204, USA.
Department of Chemistry, University of Houston, Houston, Texas 77204, USA.
Phys Rev E. 2017 Aug;96(2-1):022610. doi: 10.1103/PhysRevE.96.022610. Epub 2017 Aug 23.
We investigate the effects of geometric order and fluid rheology on the dispersion of micron-sized particles in two-dimensional microfluidic porous media. Particles suspended in a mixture of glycerol and water or in solutions of partially hydrolyzed polyacrylamide (HPAM) polymers were imaged as they flowed through arrays of microscale posts. From the trajectories of the particles, we calculated the velocity distributions and thereafter obtained the longitudinal and transverse dispersion coefficients. Particles flowed in the shear-thinning HPAM solution through periodic arrays of microposts were more likely to switch between streamlines, due to elastic instabilities. As a result, the distributions of particle velocity were broader in HPAM solutions than in glycerol-water mixtures for ordered geometries. In a disordered array of microposts, however, there was little difference between the velocity distributions obtained in glycerol-water and in HPAM solutions. Correspondingly, particles flowed through ordered post arrays in HPAM solutions exhibited enhanced transverse dispersion. This result suggests that periodic geometric order amplifies the effects of the elasticity-induced velocity fluctuations, whereas geometric disorder of barriers effectively averages out the fluctuations.
我们研究了几何排列顺序和流体流变学对微米级颗粒在二维微流控多孔介质中分散的影响。当悬浮在甘油和水的混合物或部分水解聚丙烯酰胺（HPAM）聚合物溶液中的颗粒流过微尺度柱阵列时，对其进行成像。根据颗粒的轨迹，我们计算了速度分布，进而得到纵向和横向扩散系数。由于弹性不稳定性，颗粒在剪切变稀的HPAM溶液中流过周期性微柱阵列时更有可能在流线之间切换。因此，对于有序几何结构，HPAM溶液中颗粒速度的分布比甘油 - 水混合物中的更宽。然而，在无序的微柱阵列中，甘油 - 水和HPAM溶液中获得的速度分布几乎没有差异。相应地，颗粒在HPAM溶液中流过有序柱阵列时表现出增强的横向扩散。这一结果表明，周期性几何排列顺序放大了弹性诱导速度波动的影响，而障碍物的几何无序有效地平均了这些波动。
