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Approximate calculation and measurement of the pressure distribution in radial flow of molten polymers between parallel discs
Author(s) -
Winter Horst H.
Publication year - 1975
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.760150610
Subject(s) - materials science , mechanics , power law fluid , flow (mathematics) , dimensionless quantity , power law , radius , thermodynamics , shear stress , inertia , newtonian fluid , classical mechanics , physics , mathematics , statistics , computer security , computer science
Abstract The known generalized Newtonian fluid “power law” solution of the radial flow between parallel discus has been used to estimate the normal stress, the magnitude of inertia, and the temperature changes due to viscous dissipation. The flow near the wall has been found to be “nearly steady shear flow;” thus the three viscometric functions can be expected to describe the stress at the wall. Further away from the walls, however, the flow is very different from “steady shear flow.” The temperature field in the radial flow section depends on the dimensionless parameters Nahme number, Graetz number, and ratio of inner to outer radius, as well as on the thermal initial and boundary conditions. Experimentally the radial pressure profiles for flow of three different polyethylenes and of one polystyrene have been studied. The measured pressure profiles are about 20 percent lower than the calculated ones from the “power law” solution. This discrepancy cannot yet be explained; the effects of normal stresses, of inertia, or of viscous heating in these experiments are too small to give a measurable effect.