Yagodnitsyna Anna, Kovalev Alexander, Bilsky Artur
Kutateladze Insitute of Thermophysics SB RAS, 630090 Novosibirsk, Russia.
Physics Department, Novosibirsk State University, 630090 Novosibirsk, Russia.
Micromachines (Basel). 2021 Mar 22;12(3):335. doi: 10.3390/mi12030335.
Immiscible liquid-liquid flows in microchannels are used extensively in various chemical and biological lab-on-a-chip systems when it is very important to predict the expected flow pattern for a variety of fluids and channel geometries. Commonly, biological and other complex liquids express non-Newtonian properties in a dispersed phase. Features and behavior of such systems are not clear to date. In this paper, immiscible liquid-liquid flow in a T-shaped microchannel was studied by means of high-speed visualization, with an aim to reveal the shear-thinning effect on the flow patterns and slug-flow features. Three shear-thinning and three Newtonian fluids were used as dispersed phases, while Newtonian castor oil was a continuous phase. For the first time, the influence of the non-Newtonian dispersed phase on the transition from segmented to continuous flow is shown and quantitatively described. Flow-pattern maps were constructed using nondimensional complex We·Oh depicting similarity in the continuous-to-segmented flow transition line. Using available experimental data, the proposed nondimensional complex is shown to be effectively applied for flow-pattern map construction when the continuous phase exhibits non-Newtonian properties as well. The models to evaluate an effective dynamic viscosity of a shear-thinning fluid are discussed. The most appropriate model of average-shear-rate estimation based on bulk velocity was chosen and applied to evaluate an effective dynamic viscosity of a shear-thinning fluid. For a slug flow, it was found that in the case of shear-thinning dispersed phase at low flow rates of both phases, a jetting regime of slug formation was established, leading to a dramatic increase in slug length.
当预测各种流体和通道几何形状的预期流动模式非常重要时，微通道中的不混溶液 - 液流动在各种化学和生物芯片实验室系统中得到广泛应用。通常，生物液体和其他复杂液体在分散相中表现出非牛顿特性。迄今为止，此类系统的特征和行为尚不清楚。本文通过高速可视化研究了T形微通道中的不混溶液 - 液流动，旨在揭示剪切变稀对流动模式和弹状流特征的影响。使用三种剪切变稀流体和三种牛顿流体作为分散相，而牛顿蓖麻油作为连续相。首次展示并定量描述了非牛顿分散相对从分段流到连续流转变的影响。使用无量纲复We·Oh构建流动模式图，描绘连续流到分段流转变线的相似性。利用现有的实验数据表明，当连续相也表现出非牛顿特性时，所提出的无量纲复数有效地应用于流动模式图的构建。讨论了评估剪切变稀流体有效动态粘度的模型。选择了基于整体速度的最合适的平均剪切速率估计模型，并应用于评估剪切变稀流体的有效动态粘度。对于弹状流，发现在两相流速较低且分散相为剪切变稀的情况下，建立了弹状形成的喷射模式，导致弹状长度急剧增加。
