Natu Aditya, Ghosh Uddipta
Discipline of Mechanical Engineering, Indian Institute of Technology Gandhinagar, Gujarat-382355, India.
Soft Matter. 2021 Oct 6;17(38):8712-8729. doi: 10.1039/d1sm00537e.
The flow of polymeric liquids in narrow confinements with a rectangular cross section, in the presence of electrical double layers is analyzed here. Our analysis is motivated by the fact that many of the previous studies on the flow of complex fluids tend to focus on highly idealized parallel plate channels, which are markedly different from the rectangular ducts, used in many experiments and devices. We consider the combined electroosmotic and pressure driven flows as well as the streaming potential resulting from a mechanically driven flow. We use two distinct constitutive relations to model the polymeric liquids, namely the simplified exponential Phan-Thien-Tanner (sePTT) model and the Giesekus model, both of which are non-linear viscoelastic models, capable of capturing the shear thinning behavior. We establish that the applied electric field may have a strong influence on the overall flow rate, which rapidly increases with the field strength as well as the extent of viscoelasticity of the fluid. Viscoelasticity and shear thinning behavior also enhance the streaming potential by several fold as compared to a Newtonian medium. We demonstrate that the aspect ratio of a channel has a bigger influence on the net throughput and the streaming potential, when the extent of viscoelasticity is relatively large. We illustrate that for sePTT fluids, the flow is strictly unidirectional, while for Giesekus fluids, secondary flows are inevitably present on account of their non-zero second normal stress coefficient. Although the electric field does not change the overall patterns of these secondary flows, their magnitude does depend on the imposed field strength for combined flows.
本文分析了在存在双电层的情况下，聚合物液体在具有矩形横截面的狭窄通道中的流动。我们进行分析的动机是，以往许多关于复杂流体流动的研究往往集中在高度理想化的平行板通道上，而这些通道与许多实验和设备中使用的矩形管道有显著不同。我们考虑了电渗流和压力驱动流的组合以及机械驱动流产生的流动电势。我们使用两种不同的本构关系来模拟聚合物液体，即简化指数型的Phan-Thien-Tanner（sePTT）模型和Giesekus模型，这两种模型都是非线性粘弹性模型，能够捕捉剪切变稀行为。我们发现，施加的电场可能对总体流速有很大影响，总体流速会随着场强以及流体的粘弹性程度迅速增加。与牛顿介质相比，粘弹性和剪切变稀行为还会使流动电势增强几倍。我们证明，当粘弹性程度相对较大时，通道的纵横比对净通量和流动电势有更大影响。我们表明，对于sePTT流体，流动是严格单向的，而对于Giesekus流体，由于其非零的第二法向应力系数，不可避免地会出现二次流。虽然电场不会改变这些二次流的总体模式，但它们的大小确实取决于组合流中施加的场强。
