Droplet transport dynamics induced by ultrasonic vibration on horizontal metal surface

This paper reports using ultrasonic waves to manipulate the dynamic transport of liquid droplets on a horizontal aluminum plate. A comprehensive experimental analysis was conducted to characterize the morphology evolution, velocity change, force analysis, and energy consumption of droplets under different droplet volumes (5–25 μl) and vibration velocities (0.35–0.75 m/s). The modified Weber number was introduced to construct its relationship with the droplet spreading ratio and dimensionless velocity. A prediction model and optimization strategy for droplet kinetic energy and spreading energy were established based on response surface analysis and multi-response optimization function method. Results show that the acoustic radiation force induces pronounced droplet deformation and directional migration toward the vibration antinode, with maximum instantaneous velocity reaching 85 mm/s at 25 μl–0.75 m/s condition. The proportion of ultrasonic energy converted into spreading decreases from 35% to 15% as vibration velocity increases. Furthermore, the droplet spreading energy (0.1–1 μJ) is two orders of magnitude higher than the kinetic energy (0–0.013 μJ), indicating that droplet deformation demands significantly more energy than directional transport. Optimization results show that when the droplet volume is 5–15 μl and the vibration velocity is 0.6–0.75 m/s, the droplet can reduce the waste of spreading energy while maintaining driving ability. This work provides a theoretical basis and experimental support for developing a multifunctional droplet manipulation technique.