Effect of driving frequency and power on droplet size atomized by a multimodal transducer

Weiquan Wang; Zhirui Chen; Hiroshi Hasegawa; Kohsuke Hirano; Chikahiro Imashiro; Takeshi Morita

doi:10.1016/j.ultsonch.2024.107166

Effect of driving frequency and power on droplet size atomized by a multimodal transducer

Ultrason Sonochem. 2024 Nov 19:112:107166. doi: 10.1016/j.ultsonch.2024.107166. Online ahead of print.

Authors

Weiquan Wang¹, Zhirui Chen², Hiroshi Hasegawa³, Kohsuke Hirano³, Chikahiro Imashiro², Takeshi Morita⁴

Affiliations

¹ Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa-no-ha 5-1-5, Kashiwa 277-8563, Japan.
² Graduate School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8654, Japan.
³ Development and Engineering Department, Industrial Cleaning Equipment Division, Kaijo Corporation, Sakae-cho 3-1-5, Hamura 205-8607, Japan.
⁴ Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa-no-ha 5-1-5, Kashiwa 277-8563, Japan; Graduate School of Engineering, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113-8654, Japan. Electronic address: morita@pe.t.u-tokyo.ac.jp.

PMID: 39603204
DOI: 10.1016/j.ultsonch.2024.107166

Abstract

Ultrasonic atomization is used in various applications such as medical devices, material synthesis, and humidity control. To meet the needs of different applications, the required droplet size ranges from a few microns to several hundred microns. In this study, we realized wideband multiple-frequency atomization with a multimodal transducer, which could control the size of atomized droplets by switching operating frequencies. A parabolic reflector served to focus the incident ultrasound waves, and a circular plate was employed to excite bending modes. By comparing the results of frequency response experiments with those of finite element simulation, nine different bending modes were acquired in the range of 500-2500 kHz. Then, 734, 949, 1530, and 2063 kHz were selected to examine atomization performance for producing 1-10 μm water droplets. The relationship between the droplet diameter and the operating frequency was clarified. The droplet diameter was found to follow a log-normal distribution. At these four frequencies, the mean droplet diameter was 7.71, 6.57, 4.87, and 4.43 μm, respectively, meaning that the diameter decreased with increasing frequency. The mean droplet diameter decreased with increasing input power at 734 kHz, whereas at 2063 kHz, no significant trend was shown. Furthermore, the atomization rate was found to increase at higher power and exhibited a frequency dependence. These results indicated that the multimodal transducer has promising potential for high-frequency ultrasonic atomization and the capacity to control the droplet size.

Keywords: Acoustic focusing mechanism; Droplet diameter distribution; Multimodal driving; Ultrasonic atomization.