Abstract Viscoelastic fluids have been recently proposed to promote mixing effect in microfluidic systems, where limited success has been obtained. However, the flow and mixing mechanism of a viscoelastic fluid is still poorly understood, particularly regarding the roles of injection on mixing at low Reynolds numbers. In this work, an efficient mixer by orthogonal injection into a primary flow is proposed. The mixing behaviors of shear-thinning fluids in a serpentine channel with an orthogonal injection were investigated experimentally. Dye visualization and concomitant statistical analysis were conducted to quantitatively characterize the mixing performance and to reveal the flow kinematics. Enhanced mixing is achieved just over a short effective mixing length. The probability distribution functions (PDFs) analysis shows that the mixing efficiency, defined by the normalized concentration of dye intensity (Gan et al., 2007), can be significantly improved from 22% for the Newtonian fluids to 69% and 76% by using a shear-thinning fluid with polymer concentrations of 25 and 50 ppm, respectively. The decay exponents of shear-thinning fluids plateau at -3.4 indicates the occurrence of elastic instability. The relative-change-ratio fluctuations illustrates that the observation area can generate sufficient elastic stress to induce flow instabilities, resulting in effective mixing in the channel.

中文翻译：

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低雷诺数下在微蛇形通道中正交注入剪切稀化流体的有效混合增强

摘要 最近有人提出粘弹性流体来促进微流体系统中的混合效果，但取得的成功有限。然而，粘弹性流体的流动和混合机制仍然知之甚少，特别是关于注入在低雷诺数下混合的作用。在这项工作中，提出了一种通过正交注入主流的高效混合器。实验研究了具有正交注入的蛇形通道中剪切稀化流体的混合行为。进行染料可视化和伴随的统计分析以定量表征混合性能并揭示流动运动学。仅在较短的有效混合长度上实现增强的混合。概率分布函数 (PDF) 分析表明，混合效率由归一化的染料强度浓度定义（Gan 等，2007），可以从牛顿流体的 22% 显着提高到 69% 和 76%。聚合物浓度分别为 25 和 50 ppm 的剪切稀化液。剪切稀化流体的衰减指数稳定在-3.4 表明发生了弹性不稳定。相对变化率的波动说明观测区可以产生足够的弹性应力来引起流动不稳定性，从而导致通道内的有效混合。通过使用聚合物浓度分别为 25 ppm 和 50 ppm 的剪切稀化流体，可以将牛顿流体的 22% 显着提高到 69% 和 76%。剪切稀化流体的衰减指数稳定在-3.4 表明发生了弹性不稳定。相对变化率的波动说明观测区可以产生足够的弹性应力来引起流动不稳定性，从而导致通道内的有效混合。通过使用聚合物浓度分别为 25 ppm 和 50 ppm 的剪切稀化流体，可以将牛顿流体的 22% 显着提高到 69% 和 76%。剪切稀化流体的衰减指数稳定在-3.4 表明发生了弹性不稳定。相对变化率的波动说明观测区可以产生足够的弹性应力来引起流动不稳定性，从而导致通道内的有效混合。