Interaction effects in multi-outlet viscoelastic contraction flow

• We studied viscoelastic contraction flows with multiple outlets and free outflow.
• Flow rate distribution is influenced by streamline pattern, and thus, vortex height.
• Multi-outlet contraction flow is less stable than single-outlet contraction flow.
• Flow rate distribution and fluctuations may influence extrudate quality.
• Our results are important for industrial extrusion processes.

This paper describes an experimental study of interaction effects in viscoelastic contraction flows with an array of multiple, parallel outlets. The study focuses on edge effects, that is, effects of the finite size of an array, on flow rate distribution and flow stability. The experiments were carried out with a PEG-PEO Boger fluid in glass microfluidic chips with three parallel, abrupt contractions, variable outlet spacing, and free outflow. We used micro-Particle Image Velocimetry (μ-PIV) to measure the velocity field, and particle streak imaging to visualise the flow. The two most important conclusions of our study are: 1. the flow in the three outlet case is more unsteady than in the single outlet case, which possibly leads to flow rate fluctuations in the individual outlets, and 2. if the distance between the outlets is smaller than the distance between the outer outlets and the side walls of the upstream channel, the flow rate in the central outflow channel is lower than that in the outer two channels. The difference in flow rate reduces with increasing vortex size; at the highest tested flow rates the flow rate in the middle channel is even higher than that in the outer channels. These results are relevant for industrial production processes involving multi-outlet viscoelastic extrusion flow, such as fibre spinning.

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