2020 Virtual AIChE Annual Meeting

(159j) New Converging Channel Profile for Extensional Flows: Geometrical Construct Improves Extension Rate Uniformity

Authors

Hodgkinson, R. - Presenter, The University Of Sheffield
Chaffin, S., University Of Leeds
Zimmerman, W. B., University of Sheffield
Holland, C., The University Of Sheffield
Howse, J. R., The University Of Sheffield
Extensional flows and extensional rheology play an important role in a range of processes from classical industrial operations such as polymer extrusion and fibre spinning through to dictating the behaviour of droplet formation in inkjet printing(1). Despite this, measuring extensional rheology remains challenging. Fluids of interest are typically viscoelastic (time dependant) and the duration for which a fluid packet may be extended is often experimentally limited, giving rise to a situation exemplified by the well-known “M1 muddle”(2).

Hyperbolic converging channels, combined with methods to produce wall slip, are one approach used to produce constant extension rates in extensional rheology experiments(3-5). In this work, through a novel and simple geometric construction, we have developed a new wall profile. We show, via CFD, that this simple alteration produces an improvement in extension rate uniformity for a fluid packet passing through the channel. Depending on the comparison basis, the improvement is on the order of 15%. In addition, specific aspects of a hyperbolic geometry (e.g. start point) are rarely quantifiably justified in literature. Our construction also places a finite limit on the wall location where the target extension rate can first be achieved, a useful design insight for the experimental rheologist.

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(4) Wang, J. & James, D. F. Lubricated extensional flow of viscoelastic fluids in a convergent microchannel. Journal of Rheology 55, 1103-1126, doi:10.1122/1.3613948 (2011).

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