Electro-Mechanical Modeling of Piezoelectric Fluid Ejectors for High Viscosity Liquids

date November 14, 2014
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Friday, November 14, 2014 4:00 p.m. ETC 4.150

Dr. Drew Loney
George W. Woodruff School of Mechanical Engineering
Georgia Institute of Technology

The controlled atomization of high viscosity liquids to produce individual droplets of uniform diameter remains an ongoing technological challenge. Traditional atomization techniques for the production of single droplets—inkjet printers—do not extend to high viscosity materials as fluid ejection ceases. Other atomization methods, such as horn-based ultrasonic atomization, have demonstrated the capability to atomize such materials but a detailed understanding of the mechanism that enables fluid ejection is lacking. The underlying physical mechanisms that govern atomization of high viscosity materials (> 10 mPa·s) by piezoelectric transducer-driven fluid ejectors remain poorly understood, requiring an in-depth understanding of the acoustics underlying the fluid ejection process. This presentation focuses on the principle acoustic phenomena that regulate atomization of high viscosity materials—fluid cavity/transducer interactions and waveform propagation within the fluid cavity—to ascertain an upper viscosity bound on the materials that can be atomized by piezoelectric transducer-driven fluid ejectors. A coupled electro-mechanical analytical modeling framework is developed by decomposing fluid ejector geometries into simplified acoustic elements with closed-form solutions joined together through boundary conditions. These simplified acoustic models maintain the dominant sources of viscous dissipation and dispersion within the modeling framework to provide an accurate estimate of the acoustic field amplitude which is the driving mechanism for fluid ejection. By comparing the acoustic pressure amplitude to that required to yield fluid ejection at the aperture, obtained by CFD modeling and scaling analysis, an upper limit on liquid viscosity for atomization can be determined. The electro-mechanical modeling framework is also applied to explore new concepts of piezoelectric transducer-driven fluid atomizers in an effort to achieve the controlled atomization of high viscosity materials.