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

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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