Dynamics of Flow, Particles and Bubbles in a Piezo-acoustic Inkjet Channel

Inkjet printing is celebrated for its stability and reproducibility in ejecting droplets under standard conditions. Under normal operating conditions, billions of droplets can be jetted with the same speed and volume from a single nozzle. While its primary applications are in industrial-scale printing of graphics and documents, it has also found uses in the manufacturing of electronic components, electroluminescent displays, biomaterials, pharmaceutics, and the lubrication of ball bearings, among others. Yet, inkjet performance can be compromised by unpredictable factors, such as the entrainment of air bubbles in the ink channel. This phenomenon disrupts acoustic properties and, consequently, droplet size and velocity. As entrained bubbles expand, they hinder the droplet formation process. The presence of trapped dirt particles exacerbates the likelihood of air bubble entrainment.

To enhance inkjet system stability and reliability, understanding the mechanisms behind bubble entrainment is crucial. Additionally, it is also essential to comprehend the events leading to the bubble entrainment and what happens to a bubble that has already been entrained. The research in this thesis employs a combination of experimental methods and computational modeling to investigate the interplay among the fluid flow, particles, and bubbles within the inkjet channel. The time-averaged and unsteady flow inside the ink channel, and their dependence on the driving conditions, is explored by carrying out a comprehensive flow characterization. An exploration of the effect of driving conditions on jetting stability uncovers critical parameters governing the inkjet system. The study delves into counterintuitive particle trapping, shedding light on fundamental processes that impact system performance. By dissecting the dynamics of entrained bubbles and their influence on channel acoustics, we gain deeper insights into system behavior, paving the way for advancements in inkjet technology. The present work offers valuable insights into oscillatory microfluidic flow, dirt particle entrapment in microfluidic systems, and confined bubble dynamics. Its implications extend beyond inkjet printing, encompassing diverse research areas, including pulsatile channel flows, microfluidics, cavitation, lab-on-a-chip technology, and biomedical research.