标题： 粘弹性对微流控T型结中液滴动力学和破裂的影响：格子玻尔兹曼研究 显示英文标题

标题： Effects of viscoelasticity on droplet dynamics and break-up in microfluidic T-Junctions: a lattice Boltzmann study

摘要： 粘弹性对微流体T型接头中流体丝的动态和破裂的影响通过稀释聚合物溶液的数值模拟进行研究，改变毛细管数（$\mbox {Ca}$），即改变粘性力和界面表面张力之间的平衡，直到$\mbox{Ca} \approx 3 \times 10^{-2}$。基于格子玻尔兹曼模型（LBM）的溶剂的纳维-斯托克斯（NS）描述与此处提出的彼得林闭合（FENE-P模型）的有限可扩展非线性弹性哑铃本构方程相结合。我们展示了在$\mbox{Ca}$范围内的三维模拟结果，该范围足够广泛，可以表征受限T型接头中的三种破裂机制，即${\it squeezing}$、${\it dripping}$和${\it jetting}$状态。 FENE-P本构方程的各种模型参数，包括聚合物松弛时间$\tau_P$和有限伸展参数$L^2$，被改变以提供关于粘弹性如何影响动态和断裂特性的定量细节。 我们将分析具有${\it Droplet ~Viscoelasticity}$（DV）的情况，其中粘弹性特性局限于分散（d）相，以及具有${\it Matrix ~Viscoelasticity}$（MV）的情况，其中粘弹性特性局限于连续（c）相。 在本研究中考虑了两相的中等流量比$Q \approx {\cal O}(1)$。 总体而言，我们发现MV情况下的影响更为明显，因为驱动断裂过程上游的流动可以被聚合物应力显著扰动。 显示英文摘要

摘要： The effects of viscoelasticity on the dynamics and break-up of fluid threads in microfluidic T-junctions are investigated using numerical simulations of dilute polymer solutions at changing the Capillary number ($\mbox {Ca}$), i.e. at changing the balance between the viscous forces and the surface tension at the interface, up to $\mbox{Ca} \approx 3 \times 10^{-2}$. A Navier-Stokes (NS) description of the solvent based on the lattice Boltzmann models (LBM) is here coupled to constitutive equations for finite extensible non-linear elastic dumbbells with the closure proposed by Peterlin (FENE-P model). We present the results of three-dimensional simulations in a range of $\mbox{Ca}$ which is broad enough to characterize all the three characteristic mechanisms of breakup in the confined T-junction, i.e. ${\it squeezing}$, ${\it dripping}$ and ${\it jetting}$ regimes. The various model parameters of the FENE-P constitutive equations, including the polymer relaxation time $\tau_P$ and the finite extensibility parameter $L^2$, are changed to provide quantitative details on how the dynamics and break-up properties are affected by viscoelasticity. We will analyze cases with ${\it Droplet ~Viscoelasticity}$ (DV), where viscoelastic properties are confined in the dispersed (d) phase, as well as cases with ${\it Matrix ~Viscoelasticity}$ (MV), where viscoelastic properties are confined in the continuous (c) phase. Moderate flow-rate ratios $Q \approx {\cal O}(1)$ of the two phases are considered in the present study. Overall, we find that the effects are more pronounced in the case with MV, as the flow driving the break-up process upstream of the emerging thread can be sensibly perturbed by the polymer stresses.