Today's KNOWLEDGE Share:High and low shear rate changes in Rheology

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Today's KNOWLEDGE Share

If a relatively high Mw grade flows from thin to thick, as shown in the picture, and if the time needed to fill the thick section is way shorter than the average polymer relaxation time, the polymer will not be able to reach its higher viscosity (corresponding to higher thickness/lower shear-rate). I am assuming here the polymer reached equilibrium low viscosity in the thin section, say for instance because it is much longer.


Any pressure prediction not accounting for transient rheology would then overpredict the pressure to fill.Of course the diverging flow will further complicate the situation and mess with the molecular orientation created in the thin section, but to what extent ?


Since this is more of a reasonable "conjecture", don't take this for granted, and discuss or share your opinion in the comments.

There are hundreds of Rheology papers on the "4:1 contraction flow".

Not sure I have ever seen any on the..."1:4 expansion flow" !


source:Vito leo


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