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What is the role of “pressure” in the use of capillary and slit flows to determine the shear‐rate dependent viscosity of a viscoelastic fluid?
Author(s) -
Han Chang Dae
Publication year - 2008
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.21061
Subject(s) - viscoelasticity , materials science , isotropy , capillary action , viscosity , compressibility , shear rate , mechanics , slit , shear stress , pressure gradient , composite material , apparent viscosity , shear (geology) , thermodynamics , optics , physics
The purpose of this review article is to clear the confusion created by some investigators, who erroneously thought that the pressure transducers mounted on the wall of a capillary or slit die measured a quantity that could meaningfully be called “pressure,” accurately stated “indeterminate isotropic contribution to the total stress,” and then reported on the effect of “pressure” on the shear‐rate dependent viscosity of a viscoelastic fluid. On the other hand, reference to such a quantity is not needed to calculate the wall shear stress and thus shear viscosity in fully developed flow of incompressible, viscoelastic polymer melts in a capillary or slit die; instead only information on the gradient of the total wall normal stress is needed. Further, it is pointed out that much of the literature discussing “pressure shift factor” to describe the effect of “pressure” on the viscosity of polymer melts in flow through a capillary or slit die is based on an erroneous belief that there exists a physically meaningful isotropic “pressure” that can be measured. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers.