Collaborative Research: Thermal Transport in Supercooled Droplet Freezing on Superhydrophobic and Ultrasonically Vibrating Surfaces for Enhanced De-Icing

This project will analyze what happens when supercooled water droplets hit cold surfaces. Supercooled droplets are unique because they stay liquid below the freezing point (0 C). Tiny laboratory droplets can stay liquid down to -40 C. This study will examine hidden freezing processes and the way droplets interact with surfaces. The research will explore ways to stop or delay ice buildup, which is important addressing aircraft and wind turbine icing. Ice buildup on these machines is a major problem that still causes fatal plane crashes and shuts down power production. Finally, the project will mentor high school and college students, giving them valuable, real-world experience using classroom analytical tools to solve engineering problems. This research will provide a new framework for the analysis and exploration of supercooled water droplet freezing. The freezing of supercooled water droplets occurs in two stages, The first stage is a fast transition to thermodynamic equilibrium. The second slower stage results in final solidification. Most previous studies concentrated on the slow second stage solidification process that occurs after the droplet impacts the surface, assumed a constant nucleation rate during the freezing process, or did not investigate interactions between ultrasonic waves, superhydrophobic surfaces, and droplet impact. To fill these gaps, this project will include theory and methodology development and new experimental techniques for understanding the nucleation and solidification of supercooled water droplets. The project will (a) employ ultra-fast X-ray and high-speed optical imaging to understand the physics of the freezing nucleation process when supercooled water droplets impact various solid surfaces; (b) investigate the nucleation interaction with travelling ultrasonic structural waves in the host structures; and (c) develop new multi-scale computational tools for simulating supercooled droplet freezing upon impingement. This collaborative project with coupled analytical and experimental studies will significantly improve the understanding of supercooled water droplet freezing. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.