Simulation of Onset of the Capillary Surface Wave in the Ultrasonic Atomizer.

The novel drug delivery system refers to the formulations and technologies for transporting a pharmaceutical compound in the body as it is needed to safely achieve its desired therapeutic effects. In this study, the onset vibrational amplitude of capillary surface waves for ultrasonic atomization spray is explained based on Faraday instability. Using ultrasonic frequency, the vibrational amplitude approached a critical point, and the liquid surface broke up into tiny drops. The micro-droplets were are steadily and continuously formed after the liquid feeding rate was optimized. The simulation study reported a minimum vibrational amplitude or onset value of 0.38 µm at 500 kHz frequency. The required minimum energy to atomize the drops was simulated by COMSOL Multiphysics simulation software. The simulation result agreed well with the numerical results of a subharmonic vibrational model that ocurred at 250 kHz frequency on the liquid surface. This newly designed single frequency ultrasonic atomizer showed its true physical characteristic of resonance on the fluid surface plane. Hence, this research will contribute to the future development of a single-frequency ultrasonic nebulizer and mechatronics for the generation of uniform atomized droplets.

Novel device to measure critical point "Onset" of capillary wave and interpretation of Faraday instability wave by numerical analysis.

A capillary wave was created on a surface by vibrating from the bottom of a container. When the amplitude of the container vibration approached the critical point, called the onset state, the surface broke up and bursted into very small drops on the air. The numerical analysis was used to determine the amplitude of the onset. The onset point was found to be 0.349µm at f=500kHz. The critical amplitude h(cr) was determined by using a multi-Fourier horn nozzle (MFHN) device. The onset point was measured to be 0.37µm using a laser Doppler vibrometer (LDV) with the MFHN at f=486kHz. These drops indicate that particle size distributions of 10.8µm and 7.0µm were produced by the MFHN at f=289kHz and f=486kHz, respectively. These results agreed with those obtained using Kelvin's equation, which predicted D=0.34λ.