A molecular approach to predicting the onset of drag reduction in the turbulent flow of dilute polymer solutions
A molecular approach to predicting the onset of drag reduction in the turbulent flow of dilute polymer solutions
复制标题
预测稀聚合物溶液湍流中减阻开始的分子方法
DOI：
10.1016/0009-2509(67)80215-x
复制
发表时间：
1967
影响因子：
4.7
通讯作者：
J. Zakin
中科院分区：
文献类型：
--
作者：
H. C. Hershey;J. Zakin
将影响减阻的重要变量分为流动变量和溶液变量，提出了一种预测聚合物溶液湍流流动临界雷诺数的理论。该理论指出，聚合物分子在溶液中的松弛时间等于所讨论的管子在初始湍流抑制点的特征流动时间。这相当于一个接近1的Deborah数。本研究的实验结果与基于该理论的有无减阻和湍流抑制开始时的流速的预测结果是合理一致的。在分析中没有使用可调参数。该理论似乎适用于FC[η]值大于0·10的情况。该理论预测，初始湍流抑制点处的壁面剪切速率随着约化粘度、相对分子质量和溶剂粘度的乘积的增加而减小。因此，为了获得更大的效果，这种产品应该尽可能地大。在好的和差的(Theta)溶剂中的摩擦因数测量表明，在相同的管中，在相同的流量下，差的溶剂中的最大减阻率仅为好的溶剂中的40%左右。因此，聚合物分子在溶液中的膨胀构型的效果是增加减阻。
The significant variables in drag reduction have been separated into two classifications, flow variables and solution variables.A theory has been offered which permits prediction of the critical Reynolds number in the turbulent flow of polymer solutions. The theory states that the relaxation time of the polymer molecule in solution equals a characteristic flow time for the tube in question at the point of incipient turbulent suppression. This is equivalent to a Deborah number near unity. Reasonable agreement has been shown between the experimental results of this investigation and predictions of flow rates based on this theory for the presence or absence of drag reduction and for the onset of turbulence suppression. No adjustable parameters were used in the analysis. The theory seems to be applicable at values ofC[η] greater than 0·10.The theory leads to the prediction that the wall shear rate at the point of incipient turbulence suppression decreases as the product of reduced viscosity, molecular weight and solvent viscosity increases. Thus for large effects this product should be made as large as possible.Friction factor measurements in both good and poor (Theta) solvents showed that the maximum drag reduction in the poor solvent was only about 40% of that in the good solvent at similar flow rates in the same tube. Thus the effect of an expanded configuration of the polymer molecule in solution is to increase drag reduction.