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A.H. Al-Muslimawi, H.R. Tamaddon-Jahromi, M.F. Webster
Numerical computation of extrusion and draw-extrusion cable-coating flows with polymer melts

Appl. Rheol. 24:3 (2014) 34188 (15 pages)

This paper is concerned with the numerical solution of polymer melt flows of both extrudate-swell and tube-tooling dieextrusion coatings, using a hybrid finite element/finite volume discretisation fe/fv. Extrudate-swell presents a single dynamic free-surface, whilst the complex polymer melt coating flow exhibit two separate free-surface draw-down sections to model, an inner and outer conduit surface of the melt. The interest lies in determining efficient windows for process control over variation in material properties, stressing levels generated and pressure drop. In this respect, major rheological influences are evaluated on the numerical predictions generated of the extensional viscosity and Trouton ratio, when comparing solution response for an exponential Phan-Thien Tanner (EPTT, network-based) model to that for a single extended Pom-Pom (SXPP, kinematic-based) model. The impact of shear-thinning is also considered. Attention is paid to the influence and variation in Weissenberg number We, solvent-fraction β (polymeric concentration), and second normal stress difference N2 (ξ parameter for both EPTT, and α anisotropy parameter for SXPP). The influence of model choice and parameters upon field response is described in situ through, pressure, shear and strain-rates and stress. The numerical scheme solves the momentum- continuity-surface equations by a semi-implicit time-stepping incremental Taylor-Galerkin/pressure-correction finite element method, whilst invoking a cell-vertex fluctuation distribution/median-dual-cell finite volume approximation for the first-order space-time hyperbolic-type stress evolution equation.

Cite this publication as follows:
Al-Muslimawi A, Tamaddon-Jahromi H, Webster MF: Numerical computation of extrusion and draw-extrusion cable-coating flows with polymer melts, Appl. Rheol. 24 (2014) 34188.

S.O.S. Echendu, H.R. Tamaddon-Jahromi, M.F. Webster
Modelling Reverse Roll Coating flow with dynamic wetting lines and inelastic shear thinning fluids

Appl. Rheol. 23:6 (2013) 62388 (13 pages)

This study addresses the Taylor-Galerkin/pressure-correction solution of industrial high-speed reverse roller coating flow associated with thin-film paint-coatings of strip-steel. Novel aspects lie in the inclusion of the dynamic wetting line and flow analysis due to surface tension and inelastic rheology effects, via shear-thinning and lowering high shear viscosity levels. The main aim of the study is to predict the zonal flow influences by examining viscous flow structures around the meniscus, nip and wetting line regions, conveyed via streamline and shear rate patterns, surface distributional lift and localised nip-pressures. The majority of this study focuses on the secondary nip-vortex and its influences on the contact point and dynamic wetting line. This aspect of the flow provides the driving mechanism for the onset of instabilities, which governs the entire process and tends to determine the consistency of the film thickness at the outflow. Positive peak-pressures tend to increase with decrease in nip-gap size. At low nip-gap size, negative peak pressures are observed around the substrate-wetting line contact region. At higher speed-ratios, positive peak pressures are seen to increase with less recirculation apparent around the contact zone. Significantly and upon surface tension increase, the dynamic wetting line is sucked further inwards towards the nip-gap, stimulating a localised wetting line-foil third vortex structure, which causes an apparent reduction in film-leakage thickness.

Cite this publication as follows:
Echendu S, Tamaddon-Jahromi H, Webster M: Modelling Reverse Roll Coating flow with dynamic wetting lines and inelastic shear thinning fluids, Appl. Rheol. 23 (2013) 62388.

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