Session: 03-02 Wave Propagation, Buckling, and Dynamic Response

Paper Number: 172111

172111 - Atomization of Supercooled Water Droplets Using High Frequency Structural Excitations via Piezoceramic Transducers 

The formation of ice on structures can adversely affect the performance of many systems. Ice accretions can lead to downed power lines, pipes bursting, and hazardous roads. Ice formation on airplane wings can result in a 40% lift reduction and up to 80% increase in drag for large accretions, which can lead to aerodynamic stall and has contributed to 9.5% of all fatal air accidents. It is also a major issue for wind turbine operation, as it can decrease the power generation by up to 80%. A leading factor for the ice formation is due to supercooled water droplets impacting the wings or the blades, freezing, and creating a buildup of ice. Such droplets can remain in liquid form at temperatures below 0°C, down to -40°C. Several techniques for de-icing on aircraft and/or wind turbines have been implemented such as anti-freeze chemicals, electrical-thermal resistive heating, pneumatic deicing boots, hot air bleed system, electro-mechanical, etc. Each of these systems have their own drawbacks, such as high-power requirements for electrical-thermal resistive heating, durability issues with anti-freeze chemicals, or ice bridging with the pneumatic deicing boots. Furthermore, these systems tackle de-icing after accumulation of ice, and thus they do not operate at the early stage of the process, immediately after the impact of the supercooled droplets on the surface.

This project aims to reduce ice formation through atomization of the water droplet before nucleation. Atomization creates smaller droplets that are easily broken, with a timescale smaller than nucleation, making it an effective short-term method to anti-ice before nucleation and de-ice after ice formation. The approach in this research combines water droplet atomization using high frequency piezoelectric transducer (PZT) vibration and combines with the passive method of surface roughness variation of a fabricated superhydrophobic surface.  The study spans three drop heights that are recorded with high-speed imaging using selected resonant frequencies to determine the optimal range. The active method of atomization involved adjusting frequency applied to the transducer material attached to an aluminum flat plate at a constant AC voltage supply, and variation of droplet velocity parameters. The best actuators are selected and determined through the process of frequency response and magnitudes of their amplitude of vibration.

Single and sweep frequencies are studied based on their effect on the droplet dynamics with three parameters: the spread factor, the volume ejected per millisecond, and the total energy of the atomized droplets. The combination of the three helps determines three vital objectives: the dynamics of the droplet, the change in dynamics due to vibrations, and the most effective atomization. It is observed that during atomization that the Wenzel state pining becomes more prevalent in the droplet opposed to a non-vibrating surface and it also promotes increased spreading, meaning thinner droplet lamella (droplet height on surface) and more surface area contact. Furthermore, the more it spreads, the higher the volume is ejected.  

Presenting Author: Michael Philen Virginia Tech

Presenting Author Biography: Michael Philen is a professor in the Kevin T. Crofton Department of Aerospace and Ocean Engineering
at Virginia Polytechnic Institute and State University.