Modelling and simulation of applications involving the dispensing of rheologically complex liquids

Claudio P. Fonte
Department of Chemical Engineering and Analytical Science, The University of Manchester

The ejection of rheologically complex liquids through round nozzles is a commonplace process in many industrial applications from inkjet printing and additive manufacture, to the dispensing of pharmaceutical and personal care products. Well-controlled dispensing of accurate volumes of these liquids is crucial in all of these applications. However, while the task may seem trivial, Non-Newtonian fluid properties, such as shear thinning and viscoelasticity, can often produce unexpected behaviours and challenges.

In this work, we show how numerical methods can provide reasonable predictions of how a particular liquid formulation will perform when ejected through a nozzle, by knowing its physical properties and rheological properties. We use Computational Fluid Dynamics to study the dynamics of a single pulse of inelastic and elastic fluids from round capillary tubes. More specifically, we observe how changes to the duration of the pulse and its velocity have an impact on the observed flow regimes.

From our results, we establish three main regimes: no drop detachment; single droplet formation; and satellite droplet formation. We find that viscoelasticity plays a significant role in the process of drop detachment by delaying breakup. We also find that changing the duration of the flow pulse can result in dramatically different regimes, even when the same jetted volume is kept, which can have a crucial role on the control of flow regimes for a wide range of industrial applications.