Haase A Sander, Wood Jeffery A, Sprakel Lisette M J, Lammertink Rob G H
Soft matter, Fluidics and Interfaces, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.
Phys Rev E. 2017 Feb;95(2-1):023105. doi: 10.1103/PhysRevE.95.023105. Epub 2017 Feb 9.
In this study, we investigated inelastic non-Newtonian fluid flow over heterogeneously slippery surfaces. First, we simulated the flow of aqueous xanthan gum solutions over a bubble mattress, which is a superhydrophobic surface consisting of transversely positioned no-slip walls and no-shear gas bubbles. The results reveal that for shear-thinning fluids wall slip can be increased significantly, provided that the system is operated in the shear-thinning regime. For a 0.2 wt% xanthan gum solution with a power-law index of n=0.4, the numerical results indicate that wall slip can be enhanced 3.2 times when compared to a Newtonian liquid. This enhancement factor was also predicted from a theoretical analysis, which gave an expression for the maximum slip length that can be attained over flat, heterogeneously slippery surfaces. Although this equation was derived for a no-slip/no-shear unit length that is much larger than the typical size of the system, we found that it can also be used to predict the enhancement in the regime where the slip length is proportional to the size of the no-shear region or the bubble width. The results could be coupled to the hydrodynamic development or entrance length of the system, as maximum wall slip is only reached when the fluid flow can fully adapt to the no-slip and no-shear conditions at the wall.
在本研究中，我们研究了非弹性非牛顿流体在非均匀光滑表面上的流动。首先，我们模拟了黄原胶水溶液在气泡床垫上的流动，气泡床垫是一种超疏水表面，由横向定位的无滑移壁和无剪切气泡组成。结果表明，对于剪切变稀流体，只要系统在剪切变稀区域运行，壁面滑移可显著增加。对于幂律指数n = 0.4的0.2 wt%黄原胶水溶液，数值结果表明，与牛顿液体相比，壁面滑移可增强3.2倍。这一增强因子也通过理论分析得到预测，该分析给出了在平坦的非均匀光滑表面上可达到的最大滑移长度的表达式。尽管该方程是针对比系统典型尺寸大得多的无滑移/无剪切单位长度推导出来的，但我们发现它也可用于预测滑移长度与无剪切区域尺寸或气泡宽度成比例的区域中的增强情况。这些结果可与系统的流体动力学发展或入口长度相关联，因为只有当流体流动能够完全适应壁面处的无滑移和无剪切条件时，才会达到最大壁面滑移。
