Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 11, 2020 - November 13, 2020
Nebulization technology is used in various industrial and medical fields. One of the methods of spraying liquid is the ultrasonic mesh method, in which the liquid is pushed out of the mesh with many fine holes by ultrasonic vibration. Not only the shape of each mesh hole (nozzle) but also the hole spacing (pitch) determines the spraying quality and efficiency. Last year we conducted a numerical simulation of the droplet formation process from a single mesh hole by postulating axisymmetric flow and revealed the underlying flow characteristics. The present study focuses on the interference of liquid jets as well as the subsequent droplet formation process from multiple mesh holes. Numerical simulations were done for two models with nine truncated cone nozzles of 4μm outlet diameter with two different hole pitches of 20μm and 15μm, respectively. The ultrasonic vibration is operated at 200kHz. A stable droplet formation process was observed after the 4th cycle. When the hole pitch is relatively large, liquid jets slightly repel from each other. At a small hole pitch, the backflow in the negative pressure half-cycle becomes significant. Air accumulates inside the tank, and the liquid cannot be efficiently pushed out from the nozzle in the subsequent positive pressure half cycle. The interference between the generated droplets, the details of the backflow, and the retention of bubbles in the nozzle and the tank were clarified.
