Articles techniques et présentations

The 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 the jet breakup are important indicators when designing a printhead, impacting both the apparatus size and the printing quality. Understanding how the geometry of the droplet generator, the ink properties, and the operating point impacts these indicators is then of prime importance. This article focuses on the modelling of the ink jet breakup process using COMSOL Multiphysics®. The model represents the geometry of the nozzle, and the ink-air mixture downstream with 2D-axisymmetry. The diphasic flow is laminar, and is modelled using the Laminar Flow interface, coupled with the level-set method. The ink jet generation and perturbation is controlled using a periodic positive pressure drop, from upstream to downstream the nozzle. The flow is transiently solved until a periodic solution is found. The novelty of this work is using a Navier-slip boundary condition at walls, allowing to stack all the uncertainties of the process. Once the slip parameter well 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.