Results of recent experiments and numerical simulations are presented, which have been used to establish empirical rules for the dependence of drop speed on nozzle diameter and drive amplitude for Newtonian and non-Newtonian fluids printed with a range of different ink-jet print-head technologies.Experiments were carried out with Xaar, MicroFab and Spectra Dimatix print heads and with solutions of polystyrene in diethyl phthalate as model fluids. These results are compared with predictions from recent numerical codes developed by collaborators in the University of Leeds, and from simple models for drop-on-demand fluid jetting resulting from physical laws.
An experimental setup to study the dynamics of droplet jetting from a commercially available print-head is described. A MicroFab print-head with an 80 µm diameter transparent nozzle was set to print droplets at a speed of 5 m/s at a frequency of 7 kHz. A Particle Image Velocimetry (PIV) scheme consisting of an optical microscope coupled to an ultra-high speed camera is utilized to capture the motion of particles suspended in a model transparent ink. This experimental arrangement images the flow at the centre of a glass cylindrical nozzle and above the fluid meniscus at a speed of half a million frames per second. Velocity fields are obtained an approximately 200 µm thickness layer of fluid at the inside of the nozzle. Experimental results are compared with Lagrangian finite-element numerical simulations under identical fluid and jetting conditions with good agreement.advantages, challenges and current limitations of this are discussed.
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