Jagdale Purva P, Li Di, Shao Xingchen, Bostwick Joshua B, Xuan Xiangchun
Department of Mechanical Engineering, Clemson University, Clemson, SC 29634-0921 USA.
Micromachines (Basel). 2020 Mar 8;11(3):278. doi: 10.3390/mi11030278.
A fundamental understanding of the flow of polymer solutions through the pore spaces of porous media is relevant and significant to enhanced oil recovery and groundwater remediation. We present in this work an experimental study of the fluid rheological effects on non-Newtonian flows in a simple laboratory model of the real-world pores-a rectangular sudden contraction-expansion microchannel. We test four different polymer solutions with varying rheological properties, including xanthan gum (XG), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), and polyacrylamide (PAA). We compare their flows against that of pure water at the Reynolds ( R e ) and Weissenburg ( W i ) numbers that each span several orders of magnitude. We use particle streakline imaging to visualize the flow at the contraction-expansion region for a comprehensive investigation of both the sole and the combined effects of fluid shear thinning, elasticity and inertia. The observed flow regimes and vortex development in each of the tested fluids are summarized in the dimensionless W i - R e and χ L - R e parameter spaces, respectively, where χ L is the normalized vortex length. We find that fluid inertia draws symmetric vortices downstream at the expansion part of the microchannel. Fluid shear thinning causes symmetric vortices upstream at the contraction part. The effect of fluid elasticity is, however, complicated to analyze because of perhaps the strong impact of polymer chemistry such as rigidity and length. Interestingly, we find that the downstream vortices in the flow of Newtonian water, shear-thinning XG and elastic PVP solutions collapse into one curve in the χ L - R e space.
深入理解聚合物溶液在多孔介质孔隙中的流动，对于提高石油采收率和地下水修复具有重要意义。在这项工作中，我们对实际孔隙的简单实验室模型——矩形突然收缩-扩张微通道中，流体流变学对非牛顿流的影响进行了实验研究。我们测试了四种具有不同流变特性的聚合物溶液，包括黄原胶（XG）、聚乙烯吡咯烷酮（PVP）、聚环氧乙烷（PEO）和聚丙烯酰胺（PAA）。我们在雷诺数（Re）和魏森贝格数（Wi）跨越几个数量级的情况下，将它们的流动与纯水的流动进行比较。我们使用粒子纹线成像技术来可视化收缩-扩张区域的流动，以全面研究流体剪切变稀、弹性和惯性的单独及综合影响。在无量纲的Wi-Re和χL-Re参数空间中，分别总结了每种测试流体中观察到的流动状态和涡旋发展情况，其中χL是归一化涡旋长度。我们发现，流体惯性在微通道扩张部分下游产生对称涡旋。流体剪切变稀在收缩部分上游产生对称涡旋。然而，由于聚合物化学性质（如刚性和长度）的强烈影响，流体弹性的影响难以分析。有趣的是，我们发现牛顿水、剪切变稀的XG溶液和弹性PVP溶液流动中的下游涡旋在χL-Re空间中合并成一条曲线。
