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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 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
    Interface determination in bicomponent extrusion (1988)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 28 (1988), S. 982-988 
    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: The unidirectional flow of two immiscible fluids with different viscosities in a long die of arbitrary shape is considered. Mathematically, the problem has a continuum of solutions corresponding to arbitrarily prescribed interface shapes, but experimental evidence indicates the existence of a unique interface shape with the less viscous fluid encapsulating the more viscous fluid. With the introduction of the minimum viscous dissipation principle, which postulates that the amount of viscous dissipation is minimized for a given flow rate, the problem becomes a nonlinearly constrained optimization problem. A generalized reduced gradient/finite element method combination is used to predict the interface shape when two inelastic fluids are considered. The effect of the viscosity ratio and flow-rate ratio on the interface shape is examined for different die geometries. Inner layer breakup phenomena are predicted and explained for complex die geometries.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760281507
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  • 7
    Electronic Resource
    Electronic Resource
    Free radical degradation of polypropylene: Random chain scission (1993)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 33 (1993), S. 445-454 
    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: Free-radical reactions, which are relevant in the chemical modification of polymeric materials, are discussed in relationship to their influence on random chain scission. A mathematical model is developed to calculate the entire molecular weight distribution (MWD) with the degree of chain scission as the sole parameter. This expression is identical to the one derived by Saito for the case of scission initiated by irradiation. An expression for the variation of molecular weight averages with the degree of chain scission is derived and compared with those calculated with the methods of moments found in the literature. The validity of empirical closure conditions used with moment methods is discussed. Experimental data for polypropylene (PP), degraded with organic peroxides in a single screw extruder, are compared with predictions when fitting the degree of chain scission. For a specific degradation process, the degree of chain scission is found to be proportional to the initiator level.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760330802
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  • 8
    Electronic Resource
    Electronic Resource
    Melting behavior and thermal properties of high density polythylene (1995)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 35 (1995), S. 151-156 
    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: Thermal diffusivity of high density polyethylene (HDPE) was studied over a wide range of temperatures (25 to 200°C) by melting powdered HDPE in a cylindrical mold at several pressures (101.3 to 5065 KPa gage) and recording the temperature profiles at several radial positions. The energy equation was solved numerically for cylindrical geometry. The thermal diffusivity of HDPE was fit as a function of temperature, porosity, and pressure.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760350205
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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Calendering poly(vinyl chloride): Theory and experimentsPaper presented at the 2nd Joint Meeting U.S. & Japan Soc. Rheology, Kona, Hawaii, April 1979. (1980)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 20 (1980), S. 725-731 
    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: An isothermal model for the calendering of power-law fluids which exhibit a slip boundary condition is presented. This model is based on lubrication approximation and Gaskell's theorxy. It Predicts sheet thickness, pressure distribution, velocity profiles, torque and power from rheological data for the melt and machine parameters. The predictions (sheet thickness, pressure distribution and torque) are compared with a set of experimental data for rigid poly(vinyl chloride)(PVC) provided to the authors by Solvay & Cie S.A.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760201105
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