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  • 1
    Electronic Resource
    Electronic Resource
    Three-dimensional studies on bicomponent extrusion (1990)
    Springer
    Rheologica acta 29 (1990), S. 71-87 
    Details
    ISSN: 1435-1528
    Keywords: Bicomponentextrusion ; free surfaceflows ; finite element method ; three-dimensional (3-D)-flows ; dieextrusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The present work is concerned with the mathematical modelling and numerical simulation of three-dimensional (3-D) bicomponent extrusion. The objective is to provide an understanding of the flow phenomena involved and to investigate their impact on the free surface shape and interface configuration of the extruded article. A finite element algorithm for the 3-D numerical simulation of bicomponent stratified free surface flows is described. The presence of multiple free surfaces (layer interface and external free surfaces) requires special free surface update schemes. The pressure and viscous stress discontinuity due to viscosity mismatch at the interface between the two stratified components is handled with both a double node (u−v−w−P 1 −P 2 −h 1 −h 2) formulation and a penalty function (u−v−w−P−h 1 −h 2) formulation. The experimentally observed tendency of the less viscous layer to encapsulate the more viscous layer in stratified bicomponent flows of side-by-side configuration is established with the aid of a fully 3-D analysis in agreement with experimental evidence. The direction and degree of encapsulation depend directly on the viscosity ratio of the two melts. For shear thinning melts exhibiting a viscosity crossover point, it is demonstrated that interface curvature reversal may occur if the shearing level is such that the crossover point is exceeded. Extrudate bending and distortion of the bicomponent system because of the viscosity mismatch is shown. For flows in a sheath-core configuration it is shown that the viscosity ratio may have a severe effect on the swelling ratio of the bicomponent system. Modelling of the die section showed that the boundary condition imposed at the fluid/fluid/wall contact point is critical to the accuracy of the overall solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01331802
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  • 2
    Electronic Resource
    Electronic Resource
    Three-dimensional non-isothermal extrusion flows (1989)
    Springer
    Rheologica acta 28 (1989), S. 121-133 
    Details
    ISSN: 1435-1528
    Keywords: Three dimensional flows ; die extrusion ; finite element method ; free surface flows ; non-isothermal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A three-dimensional (3-D) non-isothermal study of viscous free-surface flows with exponential dependence of viscosity on temperature is presented. The effects of non-isothermal conditions and/or geometry on the extrudate shape are investigated with a fully three-dimensional finite element/Galerkin formulation. Apart from the well known thermally induced extrudate swelling phenomenon, bending and distortion of the extrudate may occur because of temperature differences and/or geometric asymmetries. A temperature difference across the die can be imposed by heating or cooling the die walls, but can also arise because of asymmetric viscous heat generation due to the die geometry. Temperature differences affect velocity profiles because of the temperature dependence of viscosity and lead to extrudate bending, an effect known as “kneeing” in the fiber spinning industry. It is also shown numerically and confirmed experimentally that the die geometry induces extrudate bending even in the case of isothermal Newtonian flows.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01356973
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  • 3
    Electronic Resource
    Electronic Resource
    Boundary conditions for contract lines in coextrusion flows (1994)
    Springer
    Rheologica acta 33 (1994), S. 241-241 
    Details
    ISSN: 1435-1528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00437309
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  • 4
    Electronic Resource
    Electronic Resource
    Die swell and melt fracture: Effects of molecular weight distribution (1974)
    Springer
    Rheologica acta 13 (1974), S. 223-227 
    Details
    ISSN: 1435-1528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Zusammenfassung Die Formeln für die Bestimmung der Schwellrate von Kunststoffschmelzen wurden behandelt. Die kritischen Bedingungen für die Ergebnisse von Schmelzbruch und Schwellrate sind kombiniert, um das Flußverhalten beim Einsetzen der Instabilität zu erklären. Es wurde dargestellt, daß der Faktor $$\bar M_z \bar M_{z + 1} /\bar M_w^2 $$ in der Schwellrate sowie im Schmelzbruch der wichtigste Parameter ist.
    Notes: Summary The equations for determining die swell of molten polymers are discussed. The critical conditions for melt fracture and die swell results are combined in order to explain the flow behavior at the onset of instability. It is shown that the factor $$\bar M_z \bar M_{z + 1} /\bar M_w^2 $$ is the most important parameter in die swell and melt fracture studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01520879
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  • 5
    Electronic Resource
    Electronic Resource
    The role of viscoelasticity in polymer sintering (1998)
    Springer
    Rheologica acta 37 (1998), S. 270-278 
    Details
    ISSN: 1435-1528
    Keywords: Key words Sintering ; coalescence ; polymer ; surface tension ; convected Maxwell model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract An experimental study for polymer sintering has been carried out using pairs of powder particles. Although in many cases Newtonian sintering models successfully describe polymer sintering, they predict a faster coalescence rate than that observed with the polypropylene copolymer resins used in this study, indicating that factors other than the surface tension and the viscosity play a role in polymer sintering. Observations of coalescence under the microscope and rotational molding experiments suggest that melt elasticity slows down the process. Based on these findings, a mathematical model describing the complete polymer sintering process for viscoelastic fluids has been developed. The approach was similar to that of Frenkel (1945) and the convected Maxwell constitutive equations were used together with the quasi-steady state approximation. The proposed viscoelastic sintering model is capable of predicting the sintering rate slowdown observed in this study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970050114
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  • 6
    Electronic Resource
    Electronic Resource
    A computer model of plasticating extrusion (1982)
    Springer
    Rheologica acta 21 (1982), S. 481-483 
    Details
    ISSN: 1435-1528
    Keywords: Plastic ; extrusion ; mathematical model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01534324
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  • 7
    Electronic Resource
    Electronic Resource
    Boundary conditions for contacts lines in coextrusion flows (1993)
    Springer
    Rheologica acta 32 (1993), S. 513-525 
    Details
    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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  • 8
    Electronic Resource
    Electronic Resource
    Effect of Reynolds number in laminar flow through a sudden planar contraction (1985)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 31 (1985), S. 1736-1739 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690311020
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  • 9
    Electronic Resource
    Electronic Resource
    Transient free-surface flows in injection mold filling (1988)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 34 (1988), S. 403-410 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Advancing and colliding flow fronts are important fluid mechanical problems in injection mold filling. These are small-scale, transient free-surface flows with a significant impact on the molecular orientation of molded parts. This paper describes a numerical technique for the simulation of transient free-surface flows. The algorithm combines a Galerkin/finite-element discretization of the governing equations with a predictor-corrector scheme for integration in time, and determines simultaneously the flow field and the free surface at every time step. The method is applied to the start-up of a fluid flow initially at rest and impingement of two flow fronts to form a weldline. Comparison of simulation with available experiments on the start-up problem shows very good agreement. Numerical tracking of fluid elements clarifies various aspects of flow-induced deformation of the material.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690340307
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  • 10
    Electronic Resource
    Electronic Resource
    Finite-element simulation of stratified multiphase flows (1987)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 33 (1987), S. 410-422 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The analysis of stratified multiphase flow fields is difficult because the position of the interface is unknown a priori and there is a discontinuity in the normal viscous stress and/or pressure at the interface. A finite-element technique that uses double nodes along the interface has been implemented. The immiscible liquid displacement in a capillary tube was examined in detail. Fountain flow in the advancing fluid, reverse fountain flow in the receding fluid, and a recirculating flow region in the less viscous fluid were determined. In Newtonian flat film coextrusion the entry region, where the two immiscible fluids form an interface, and the characteristic swelling and bending of the extrudate at the die exit were studied. The computational results compare favorably with available experimental observations.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690330307
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