Flow patterns in polyethylene and polystyrene melts during extrusion through a die entry region: measurement and interpretation

White, James L.; Kondo, Akio

doi:10.1016/0377-0257(77)80011-6

Cited by 121 publications

(17 citation statements)

References 51 publications

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“…The 5.75:1 axisymmetric contraction data from White and Kondo [29], showed clearly larger opening angles. The modification in Eq.12 aims to partially isolate the large values of 2 f caused by elongational flow, from the rotational content of the flow.…”

Section: Discussionmentioning

confidence: 99%

“…Experimental data for vortex opening angle is available for the former geometry [29]. Both the original constraint release formulation, 'MSF model CR1', and the modified formulation, 'MSF model CR2' were applied to the flows, along with the earlier fit-function MSF model [10], which we refer to as 'MSF without CCR', for comparison.…”

Section: Simulation Proceduresmentioning

confidence: 99%

“…It has not been shown that a time-integral constitutive model can fit all viscometric rheological data for IUPAC LDPE, and also match the vortex opening angle data in a 5.75:1 axisymmetric contraction flow measured by experiment by White and Kondo [29]. Concurring with such experimental data is an important requirement for a constitutive model, since it tests a model's response in a non-viscometric flow, containing a mixture of elongation and shear.…”

Section: Introductionmentioning

confidence: 99%

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A modification of the convective constraint release mechanism in the molecular stress function model giving enhanced vortex growth

Olley

Wagner

2006

Journal of Non-Newtonian Fluid Mechanics

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The molecular stress function model with convective constraint release (MSF with CCR) constitutive model [J. Rheol. 45 (2001), 1387] is capable of fitting all viscometric data for IUPAC LDPE, with only two adjustable parameters (with difference found only on reported "steady-state" elongational viscosities). The full MSF with CCR model is implemented in a backwards particle-tracking implementation, using an adaptive method for the computation of relative stretch that reduces simulation time many-fold, with insignificant loss of accuracy. The model is shown to give improved results over earlier versions of the MSF (without CCR) when compared to well-known experimental data from White and Kondo [J. non-Newt. Fluid Mech., 3 (1977), 41]; but still to under-predict contraction flow opening angles. The discrepancy is traced to the interaction between the rotational dissipative function and the large stretch levels caused by the contraction flow. A modified combination of dissipative functions in the constraint release mechanism is proposed, which aims to reduce this interaction to allow greater strain hardening in a mixed flow. The modified constraint release mechanism is shown to fit viscometric rheological data equally well, but to give opening angles in the complex contraction flow that are much closer to the experimental data from White and Kondo. It is shown (we believe for the first time) that a constitutive model demonstrates an accurate fit to all planar elongational, uniaxial elongational and shear viscometric data, with a simultaneous agreement with this well-known experimental opening angle data. The sensitivity of results to inaccuracies caused by representing the components of the deformation gradient tensor to finite precision is examined; results are found to be insensitive to even large reductions in the precision used for the representation of components. It is shown that two models that give identical response in elongational flow, and a very similar fit to available shear data, give significantly different results in flows containing a mix of deformation modes. The implication for constitutive models is that evaluation against mixed deformation mode flow data is desirable in addition to evaluation against viscometric measurements.

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Section: Discussionmentioning

confidence: 99%

Section: Simulation Proceduresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A modification of the convective constraint release mechanism in the molecular stress function model giving enhanced vortex growth

Olley

Wagner

2006

Journal of Non-Newtonian Fluid Mechanics

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“…Although several studies exist on the flow patterns in converging flows, the present understanding of the precise mechanism for the secondary flow is far from complete [1][2][3]. It has been suggested that the steady sink flow for an entry half-angle that is *) The main part of this paper was presented at the IX.…”

mentioning

confidence: 99%

Inertia effect in conical converging flow of viscoelastic fluids

Schümmer

1986

Rheol Acta

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Abstract:The convergent flow of viscoelastic fluids in conical nozzles has been examined. The experimentally determined streamlines agreed with those obtained from calculations with an approximation up to l) "2. Because of the elasticity of the fluid a rotationally symmetric eddy arises. It clings to the wall whereas the output flow proceeds in the middle. Whenanother eddy can arise in front of the first one. This second eddy is situated in the middle and causes the output to proceed as a flow near the wall. The higher the afore-mentioned dimensionless value is, the higher is the inclination of the flow to instability.

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“…The relationship among the change in the flow field, the circular secondary flow and the stress field was discussed in these studies. It was recognized that the circular secondary flow works as a stress relief mechanism [9] and relaxes the stress growth.…”

mentioning

confidence: 99%

Numerical Analysis of Viscoelastic Start-up Flow in Channels with a Tapered Contraction

Yamamoto

Nakamura

1997

Journal of the Textile Machinery Society of Japan

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Start-up flow of viscoelastic fluid in two-dimensional channels with a four to one tapered contraction was numerically analyzed using the finite element method, and the transient behavior of viscoelastic flow was discussed. The Leonov model was applied to describe the rheological behavior of the fluid.In the flow through the tapered contraction, the velocity gradient in the flow direction, 9u/8x, along the center line became smaller than that in the flow through an abrupt contraction, and the maximum of the normal stress difference, TXX -Tyy, in the tapered contraction channel was also smaller than that of the flow in the abrupt contraction channel.The peak position of 8u/8x moved with time, and this phenomenon has not been observed in the numerical simulation of the start-up flow in the channel with the abrupt contraction.

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Flow patterns in polyethylene and polystyrene melts during extrusion through a die entry region: measurement and interpretation

Cited by 121 publications

References 51 publications

A modification of the convective constraint release mechanism in the molecular stress function model giving enhanced vortex growth

A modification of the convective constraint release mechanism in the molecular stress function model giving enhanced vortex growth

Inertia effect in conical converging flow of viscoelastic fluids

Numerical Analysis of Viscoelastic Start-up Flow in Channels with a Tapered Contraction

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