FOM PhD on inkjet printing: How do meniscus shape instabilities lead to air entrapment in piezo-acoustic inkjet printing? (experiments, numeric, theory)The Challenge: In piezo-acoustic ink-jet devices a voltage pulse applied to a piezo-electric element causes the ink-filled channel to deform, thereby creating a pressure wave in the ink, ultimately leading to the jetting of droplets out of the nozzle. A notorious problem in these systems is the entrainment of tiny air bubbles during operation. Once entrained, the bubbles grow by rectified diffusion, consequently disrupt the pressure waves and finally seriously disturb the droplet formation process. Though in the last years we have made considerable progress in detecting bubbles and monitoring their growth, the exact mechanism and the exact conditions of the entrainment process at the nozzle remain elusive. The same holds for the underlying meniscus instabilities. The objective of this project is to understand these instabilities and to be able to predict under what conditions bubble entrainment will take place. The working hypothesis is that either a Rayleigh-Taylor or a capillary instability of the meniscus is responsible for the entrainment. The probability of air entrapment is strongly related to the extreme displacement of the meniscus relative to the nozzle edge and, related to this, the filling with ink of the nozzle. On the experimental side, we will use high-speed imaging techniques in order to visualize the entrainment. On the numerical side we will use two models developed by Océ based on commercial CFD codes (Ansys, Fluent, Flow3D), an in-house boundary integral code, and an in-house level set code to describe the movement of the accelerated meniscus and its interaction with the nozzle wall and the surrounding air. The available control parameters are the driving pulse (shape and amplitude), the driving pressure, the driving frequency, the nozzle shape, size and wettability properties, and the material properties of the ink such as viscosity and surface tension. Our Offer: We offer a very challenging position in an inspiring multidisciplinary and international environment. As a PhD candidate you will be offered a fulltime (38 hours /week) positions for 4 years. You will be appointed in the service of Foundation for Fundamental Research on Matter (FOM). FOM assist new foreign employees with housing and visa applications and compensates moving expenses Our group has excellent international contacts and outstanding intellectual and technological infrastructure. Your profile: We seek highly talented, enthusiastic, and exceptionally motivated candidates with an M.Sc. degree in Physics or engineering. The candidate must have strong communication skills, including fluency in written and spoken English. The position will be open until a suitable candidate is identified. An interview and a scientific presentation will be part of the selection process.
Information and Applications
For more information and applications, please contact Prof. Dr. Detlef Lohse, Physics of Fluids, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands.