理解稀聚合物溶液在通道流动中压降的理论-实验差异
Understanding the Theory--Experiment Discrepancy in Pressure Drop of Dilute Polymer Solutions in Channel Flows
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中文总结 AI 辅助
研究稀聚合物溶液在通道流动中压降的理论-实验差异，采用两种压力传感系统测量不同通道压降，指出差异源于测量解释及条件假设不匹配，建议用含更现实微观特征的本构模型改进。
中文摘要 AI 辅助
几十年来，研究人员通过实验观察到，稀粘弹性聚合物溶液通过收缩或收缩-扩张通道的流动结果与理论和模拟不符。特别是，实验报道的压降大于具有相同剪切粘度的广义牛顿参考流体，而本构模型预测在低雷诺数和小魏森贝格数或德博拉数下的稳定流动条件下压降较小。本文采用两种不同类型的压力传感系统测量不同几何形状通道的压降，结果表明上述明显差异可归因于测量解释不当以及实验条件与理论和数值研究假设之间的不匹配。研究结果表明，使用包含聚合物溶液更现实微观特征的连续介质本构模型可实现定量改进。
英文摘要
For decades researchers have experimentally observed that the flow of dilute viscoelastic polymer solutions through contraction or contraction--expansion channels yields results at odds with theory and simulations. In particular, the experimentally reported pressure drops are larger than those of generalized Newtonian reference fluids with the same shear viscosity, while constitutive models, such as Oldroyd-B and FENE-P, predict smaller pressure drops under conditions of low Reynolds numbers and stable flow at small Weissenberg ($Wi$) or Deborah ($De$) numbers. This apparent contradiction between experiments and theory has been a long-standing puzzle in the field. Here, we characterize the properties of dilute viscoelastic polymer solutions and employ two distinct types of pressure-sensing systems, conventional recessed pressure taps and flush-mounted diaphragm sensors, to systematically measure pressure drops across channels of different geometrical configurations. These measurements yield qualitative agreement with theoretical predictions across all geometries if the largest relaxation time is adopted for the analysis of the flow. Our results indicate that the apparent discrepancies mentioned above can be attributed to improper interpretation of the measurements and to mismatches between experimental conditions and assumptions made in the theoretical and numerical studies, which include hole pressure effects, the choice of relaxation time of the fluid, and the presence of experimental flow instabilities. For quantitative improvements, our results suggest the use of continuum-level constitutive models containing more realistic microscopic features of polymer solutions.
