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Old   May 6, 2004, 03:46
Default molten plastic
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Would like to enquire if molten plastic is classified as a non-newtonian fluid.

Need to model some form of plastic extrusion molding in COSMOS FloWorks. So far I've just been using some value for dynamic viscosity.

Thank you.
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Old   May 7, 2004, 03:27
Default Re: molten plastic
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Plastics and polymes are complex materials (the polymer molecule is a very long chain, nothing similar to water or air). This could induce some non-isotropic behavior known as viscoelasticity leading to large die swell. But without going that far, neglecting the shear thinning behavior of the plastic will strongly impact the accuracy of your results especially for the extrusion process where shear thinning is p-laying a major role. Non-Newtonian behavior and more specifically Generalized Newtonian behavior could have the viscosity decreasing by several orders of magnitude, therefore affecting the pressure drop no mentioning the flow pattern. I would strongly encourage you to involve such behavior. Simple models like the power law or better the Bird-Carreau law are already doing a good job.

I hope this helps
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Old   May 10, 2004, 09:12
Default Re: molten plastic
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Hi Thierry, thank very much for the input. It certainly does help.

Fortunately COSMOS FloWorks does include the power law and Carreau models for non-newtonian flow.

Thanks again.

Rgds, Koh
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