论文标题
流体粘弹性抑制了由于电动不稳定性而引起的混乱对流和混合
Fluid viscoelasticity suppresses chaotic convection and mixing due to electrokinetic instability
论文作者
论文摘要
当在电场的影响下将两种不同电导率的两种流体并排在微流体设备中并排运输时，在某些施加的电场强度和电导率比的临界值之后，通常会产生电动不稳定性（EKI）。许多先前的实验和数值研究表明，这种现象会导致微电位内的混乱流场，从而促进了两种流体在行为上的混合。然而，目前的数值研究表明，如果流体是粘弹而不是牛顿弹性的，则可以抑制由于电动不稳定性而产生的混乱对流。 In particular, we observe that as the Weissenberg number (ratio of the elastic to that of the viscous forces) gradually increases and the polymer viscosity ratio (ratio of the solvent viscosity to that of the zero-shear rate viscosity of the polymeric solution) gradually decreases, the chaotic fluctuation inside a T microfluidic junction decreases within the present range of conditions encompassed in this study.我们证明，这种混乱运动的抑制是由于在两种流体的界面处形成了高弹性应力的链。我们进一步表明，这种混沌波动（尤其是一个跨度）的抑制抑制了两种粘弹性流体的混合。因此，当计划使用EKI现象来混合这种粘弹性流体时，需要谨慎。我们的观察结果与针对这些类型的粘弹性流体进行的有限实验研究中看到的观察结果一致。
When two fluids of different electrical conductivities are transported side by side in a microfluidic device under the influence of an electric field, an electrokinetic instability (EKI) is often generated after some critical values of the applied electric field strength and conductivity ratio. Many prior experimental and numerical studies show that this phenomenon results in a chaotic flow field inside a microdevice, thereby facilitating the mixing of two fluids if they are Newtonian in behaviour. However, the present numerical study shows that this chaotic convection arising due to the electrokinetic instability can be suppressed if the fluids are viscoelastic instead of Newtonian ones. In particular, we observe that as the Weissenberg number (ratio of the elastic to that of the viscous forces) gradually increases and the polymer viscosity ratio (ratio of the solvent viscosity to that of the zero-shear rate viscosity of the polymeric solution) gradually decreases, the chaotic fluctuation inside a T microfluidic junction decreases within the present range of conditions encompassed in this study. We demonstrate that this suppression of the chaotic motion occurs due to the formation of a strand of high elastic stresses at the interface of the two fluids. We further show that this suppression of the chaotic fluctuation (particularly the span-wise one) inhibits the mixing of two viscoelastic fluids. Therefore, one needs to be cautious when the EKI phenomenon is planned to use to mix such viscoelastic fluids. Our observations are in line with that seen in limited experimental studies conducted for these kinds of viscoelastic fluids.
