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Question: Modelling thermoplastics' viscosity with varying shear and temperature

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Old   June 19, 2019, 09:39
Post Question: Modelling thermoplastics' viscosity with varying shear and temperature
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G Brown
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Hi Fluent forums,

I am trying to model the flow of a thermoplastic (PETG) through the channel pictured in 2D cross section below (inlets on right). The inlet velocity is 2.5 mm/s with a temperature of 293 deg c. Inlet diameters are 3mm for scale.



I am aware that PETG is a non-newtonian fluid so it's viscosity varies with shear rate. Furthermore, the PETG is being heated by the channel walls (473 deg c) as it moves through - so viscosity will also be varying with temperature.

I am aware that there are a few viscosity models that can be used in the material properties tab (carreau, herschel-bulkley etc). My question is - which of these models would be best suited to my case and why?

Also as a bonus question - I am currently using the thermal conductivity and specific heat capacity of solid PETG. How much will these values vary as the PETG reaches the glass transition temp and above?

Would really appreciate any thoughts you have on this!

Thanks a lot
Guy
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ansys fluent 19.2, material properties, non-newtonian fluid, thermoplastic, viscosity

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