Presheared Extensional Flow of Dilute Polymer Solutions
作者:
David F. James,
Brian D. McLean,
John H. Saringer,
期刊:
Journal of Rheology
(AIP Available online 1987)
卷期:
Volume 31,
issue 6
页码: 453-481
ISSN:0148-6055
年代: 1987
DOI:10.1122/1.549933
出版商: The Society of Rheology
数据来源: AIP
摘要:
Dilute solutions of polyethylene oxide (PEO) and polyacrylamide (PAM) were subjected to shearing and then extensional motion in order to determine the influence of prior shear on the extensional resistance of these fluids. The work was originally motivated by the explanation of drag reduction by polymer additives and so the tests were conducted in a flow cell designed to simulate the ejection event (burst) in a turbulent boundary layer flow. The results show that prior shear had a considerable effect on the PEO solutions, causing significant extensional resistance at strain rates of order102 s−1,while rates one order higher were necessary to generate an extensional effect when there was no prior shear. For the PAM solutions, on the other hand, extensional resistance depended only weakly on prior shear, and onset strain rates and resistance magnitudes depended more markedly on the ionic strength of the solvent. Tests with NaCl andCaCl2in the solvent identicated that Na and Ca ions affect the extension of PAM molecules in different ways. A flow visualization study revealed that the flow patterns for water and PEO solutions were the same but those for PAM solutions were always unsteady.
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