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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
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Optimization of distillation units using collocation models (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 813-825 
    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: Reduced-order models are developed based on orthogonal collocation on finite elements for the steady-state optimization of multicomponent distillation units. The formulation divides the column sections into subdomains (finite elements) to track irregularities in the column profiles accurately and requies that plates with discontinuities in the flows introduced by feedstreams or sidestreams should be treated as discrete equilibrium stages. Application of the model formulation to a number of examples show that reduced-order models converge to the same optimal solution as the full-order, tray-by-tray model. Optimization results show that computational time can be reduced significantly using the more compact model formulation, and it is possible to converge to the optimal solution from a larger region for the initial set of variable values.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400508
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Three-dimensional extrudate swell of creeping Newtonian jets (1988)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 34 (1988), S. 2088-2094 
    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: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690341222
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  • 9
    Electronic Resource
    Electronic Resource
    A finite element convergence study for shear-thinning flow problems (1988)
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 8 (1988), S. 123-138 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/fld.1650080202
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  • 10
    Electronic Resource
    Electronic Resource
    Finite element simulation of fountain flow in injection molding (1986)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 26 (1986), S. 449-454 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Fountain flow is the phenomenon of deceleration and outward motion of fluid particles as they approach a slower moving interface. The use of a general purpose finite element program for the appropriate boundary conditions made possible the detailed flow description behind an advancing liquid front moving at constant speed inside two-dimensional channels and tubes. The results were qualitatively the same for both Newtonian and shear-thinning fluids.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760260702
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