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Boundary conditions for contacts lines in coextrusion flows (1993)

Torres, A. ; Hrymak, A. N. ; Vlachopoulos, J. ; [et al.]

Springer

Rheologica acta 32 (1993), S. 513-525

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ISSN: 1435-1528

Keywords: Coextrusion ; interfaces ; contact lines ; multilayer flows

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Physics

Notes: Abstract A bicomponent coextrusion process is modelled using a 3-D finite element formulation. The layer uniformity problem in coextrusion is addressed by examining the effects of the polymer melt/polymer melt/die wall contact line boundary condition. It has been observed that the less viscous polymer layer will tend to displace the more viscous polymer layer near the die wall. The behaviour of the contact lisle is considered to be either a “stick” or “slip” boundary condition. In the “stick” boundary condition, the contact line does not move from its original position after the two polymer layers meet, A slip boundary condition allows the contact line to move along the die wall. The calculated interfaces which result from different contact line assumptions are determined. Results show that if a “stick” boundary condition is appropriate for a given fluid/fluid/solid contact line, then a very thin entrained layer of the more viscous polymer melt will be trapped between the less viscous polymer melt and the die wall. Slip boundary conditions would allow complete displacement of the contact line along the die wall. Both slip and stick boundary conditions produce similar interface profiles far away from the die wall for small viscosity ratios. In certain eases, the displacement of the more viscous material by the less viscous material will cease and a static interface structure is produced regardless of die length. Experimental work with polycarbonate melts is compared with the numerical simulations.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00369067

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A finite element convergence study for shear-thinning flow problems (1988)

Karagiannis, A. ; Mavridis, H. ; Hrymak, A. N. ; [et al.]

Chichester : Wiley-Blackwell

International Journal for Numerical Methods in Fluids 8 (1988), S. 123-138

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ISSN: 0271-2091

Keywords: Finite elements ; Shear-thinning flow ; Convergence study ; Newton-Raphson ; Picard Dominant eigenvalue ; Broyden ; Engineering ; Engineering General

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: The solution of the non-linear set of equations arising from the application of the finite element method to non-Newtonian fluid flow problems often requires large amounts of computer time. Four iteration schemes (Picard, Newton-Raphson, Broyden and Dominant Eigenvalue method) are compared in three different flow geometries using a shear-thinning fluid model. Points of comparison involve the computer time necessary to converge the equations, ease of implementation, radius of convergence and rate of convergence.

Additional Material: 10 Ill.