A numerical and experimental study on the process of droplet formation in a T-junction microchannel with a shear-thinning continuous phase is presented. Simulations are performed using a three-dimensional lattice Boltzmann multicomponent model. The shear-thinning behaviour is modeled using the Carreau-Yasuda model and validated with our experiments involving both Newtonian and non-Newtonian continuous phases. Using the validated numerical framework, a parametric study is performed to quantify the effect of the rheological parameters, namely the power-law index ($n$) and the Carreau number ($Cr$), on the droplet size for two different capillary numbers. To understand the variation in the droplet size and shape with the shear-thinning parameters, the dynamics of droplet breakup process is analyzed in terms of the upstream pressure build-up and the shear stresses acting on the interface of the two fluids. Our numerical results show that the dynamics of droplet formation shifts from the “shear-dominated” dripping regime to “pressure-dominated” squeezing regime for continuous phase fluids having lower values of $n$ and higher values of $Cr$. Hence, an increase in the droplet size and a change in its shape from spherical to plug is observed for fluids showing a higher shear-thinning tendency (higher $Cr$ and lower $n$). Finally, an analysis of the transition in the droplet flow regimes with a shear-thinning continuous phase at high capillary numbers is presented. For $Ca\ge 0.1$, an increase in the shear-thinning of the continuous fluid is shown to shift the droplet flow pattern from parallel flow (PF) to droplets in the channel (DC) to eventually forming droplets at the T-junction (DTJ).

中文翻译：

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具有剪切稀化连续相的T形微流控装置中液滴形成和流态转变的动力学

提出了在具有剪切稀化连续相的T型结微通道中液滴形成过程的数值和实验研究。使用三维晶格玻尔兹曼多组分模型进行模拟。剪切稀化行为是使用Carreau-Yasuda模型建模的，并通过涉及牛顿和非牛顿连续相的实验进行了验证。使用经过验证的数值框架，进行参数研究以量化流变参数（即幂律指数（$ñ$）和Carreau编号（$C\mathrm{[R}$），在两个不同毛细管数的液滴尺寸上。为了了解液滴厚度和形状随剪切稀化参数的变化，根据上游压力的增加和作用在两种流体界面上的剪切应力来分析液滴破碎过程的动力学。我们的数值结果表明，对于具有较低值的连续相流体，液滴形成的动力学从“剪切为主”的滴落状态转变为“压力为主”的压榨状态。$ñ$ 和更高的值 $C\mathrm{[R}$。因此，对于具有较高剪切稀化趋势（较高）的流体，可以观察到液滴尺寸的增加以及其形状从球形到堵塞的变化。$C\mathrm{[R}$ 和更低 $ñ$）。最后，对在高毛细管数下具有剪切稀化连续相的液滴流态中的过渡进行了分析。对于$C\mathrm{一种}\ge 0.1$，连续流体的剪切稀化的增加显示为将液滴的流动模式从平行流（PF）转移到通道（DC）中的液滴，最终在T型结（DTJ）处形成液滴。