Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences ETH Zurich, 8093 Zurich, Switzerland.
Langmuir. 2010 Jan 5;26(1):10-8. doi: 10.1021/la903982n.
The breakup of dense aggregates in an extensional flow was investigated experimentally. The flow was realized by pumping the suspension containing the aggregates through a contracting nozzle. Variation of the cluster mass distribution during the breakage process was measured by small-angle light scattering. Because of the large size of primary particles and the dense aggregate structure image analysis was used to determine the shape and structure of the produced fragments. It was found, that neither aggregate structure, characterized by a fractal dimension d(f) = 2.7, nor shape, characterized by an average aspect ratio equal to 1.5, was affected by breakage. Several passes through the nozzle were required to reach the steady state. This is explained by the radial variation of the hydrodynamic stresses at the nozzle entrance, characterized through computational fluid dynamics, which implies that only the fraction of aggregates whose strength is smaller than the local hydrodynamic stress is broken during one pass through the nozzle. Scaling of the steady-state aggregate size as a function of the hydrodynamic stress was used to determine the aggregate strength.
采用泵送含有团聚体的悬浮液通过收缩喷嘴的方法来实验研究了在拉伸流中团聚体的破碎过程。采用小角光散射法测量了团聚体在破碎过程中质量分布的变化。由于初级粒子尺寸较大且团聚体结构致密，因此采用图像分析的方法来确定生成的碎片的形状和结构。结果发现，无论是由分形维数 d(f) = 2.7 所表征的团聚体结构，还是由平均纵横比等于 1.5 所表征的形状，都没有受到破碎的影响。需要经过几次通过喷嘴才能达到稳定状态。这可以通过计算流体动力学来解释，在喷嘴入口处的流体动力应力的径向变化，这意味着只有在通过喷嘴的一次通过中强度小于局部流体动力应力的团聚体分数被破碎。作为流体动力应力函数的稳态团聚体尺寸的标度用于确定团聚体强度。
