Mixing viscoelastic fluid flows at the micro scale

诸如提高石油/天然气采收率、涂层和封装等应用涉及多相流，其中流变行为和界面动力学对结果起主要作用。这些工艺中的许多需要添加聚合物和表面活性剂，以减少摩擦，促进乳化或改善润湿等。这些添加剂，即使在极少量添加时，也会对流体性质产生显著影响，特别是在粘弹性和表面张力方面，从而影响流体的流动行为。对于牛顿流体，在低雷诺数（Re）下的流动主要由扩散控制，并倾向于保持层流。因此，两种不混溶流体的混合，例如以产生乳液或以置换其中一个相，例如在强化采油中，对于非常粘稠的系统或小规模的流动，固有地难以有效实现。然而，当少量的高分子量聚合物被添加到水（或任何牛顿溶剂）中，使溶液粘弹性，然后流体流动在任意小的Re值已被证明表现出不稳定性和“类粘性”特性和湍流混合的东西更有效。已有研究表明，在小尺度下，由于表面效应的增强，弹性湍流的作用将大大增强。本研究的目的是从根本上研究这种“弹性”湍流对单相和多相系统，特别是不混溶的两种液体系统的混合效果。我们计划利用正则流和简单微流体流，其提供了剪切和延伸的组合，以理解在良好控制的条件下在更复杂的流动中出现的一系列现象，并因此解决了许多工程应用：通过多孔介质的流动、在油/回收应用中去除神经节、在不利条件下产生乳液。

Applications such as enhanced oil/gas recovery, coatings and encapsulation involve multiphase flows where rheological behaviour and interfacial dynamics plays a major part on the outcomes. Many of these processes require the addition of polymers and surfactants, to reduce friction, promote emulsification or improve wetting, among others. These additives, even when added in extremely small quantities, have a significant impact on the fluid properties, particularly in terms of its viscoelasticity and surface tension, with consequent impact on the flow behaviour.For Newtonian fluids, flows at low Reynolds numbers (Re) are dominated by diffusion and tend to remain laminar. As a consequence mixing of two immiscible fluids, e.g. to create an emulsion or to displace one of the phases such as in enhanced oil recovery, is inherently difficult to achieve efficiently for very viscous systems or flows at small scales. However, when a small amount of high molecular-weight polymer is added to water (or any Newtonian solvent), making the solution viscoelastic, then fluid flows at arbitrarily small values of Re have been shown to exhibit instabilities and "turbulent-like" characteristics and turbulent flows mix things much more efficiently. It has been shown that small length-scales, in which surface effects are enhanced, accentuate the role of elasticity to levels far beyond those typical at conventional scales.The purpose of this project is to fundamentally investigate the mixing effectiveness of this "elastic" turbulence for single and multiphase systems and, in particular, for immiscible two liquid systems.We plan to make use of canonical flows and simple microfluidic flows, which provide a combination of shear and extension, to understand under well-controlled conditions a range of phenomena arising in much more complicated flows and as such address a number of engineering applications: flow through porous media, removal of ganglia in oil/recovery applications, creation of emulsions under adverse conditions.