Modelling of Ink Jet Breakup using COMSOL Multiphysics®

Continuous inkjet technology is widely used in the industry for marking and coding, and reposes on the emission of charged droplets at high velocity and high frequency. The shape of the droplets and the length needed for jet breakup are significant factors in the design of a printhead, influencing both the apparatus size and the printing quality. Understanding how the geometry of the droplet generator, the ink properties, and the operating point impact these indicators is then of prime importance. This article presents a modelling approach to the ink jet breakup process using COMSOL Multiphysics®.

The model represents the geometry of the nozzle, and the ink-air mixture downstream in 2D-axisymmetry. The diphasic flow is laminar, and is modelled using the Laminar Flow interface, coupled with the level-set method. The generation and perturbation of the ink jet are controlled using a periodic positive pressure drop, from upstream to downstream of the nozzle. The transient flow is solved until a periodic solution is found. The novelty of this work is the use of a Navier-slip boundary condition at walls, allowing to stack all process uncertainties. Once the slip parameter is fitted, this method enables an accurate prediction of the ink jet breakup in multiple configurations. The model can then be used to predict the shape of the droplets and the breakup length of new configurations, which may save weeks of experimental work.