Invited Speakers

Shu Takagi (The University of Tokyo)

Microbubble generation in T-Junction-type Microchannel

Title: High-speed measurement of bubble generation process in microchannel and bubble manipulation in ultrasound field
Author: Shu Takagi
Affiliation: Professor, The University of Tokyo
Email: takagi[at]mech.t.u-tokyo.ac.jp
URL: http://www.fel.t.u-tokyo.ac.jp/takagi/takagi_e.html
(a) Simple T-Shape (b) Orifice Type
In this talk, two topics related to the microbubble behaviors are presented with High-speed camera observation. One is microbubble generation using microchannel and the other is microbubble manipulation in ultrasound field.
MicroBubble Generation using microchannel
A technique to generate µm-order bubbles have been developed using a microchannel with a squeezed T-junction. The mechanism of bubble generation was investigated through the observation using the developed Ultrahigh-speed micron-resolution particle tracking velocimetry (UH-µPTV) method [1]. The experiments were conducted for several types of channels with the different cross-section sizes to examine the effect of the cross-section size of the channels. Two of the typical snapshots of generated microbubbles are shown in Fig.1. In the experiment shown in right figure (b), bubbles of mono-dispersed 6.1µm diameter were generated through the suitable design of channel shape for generating smaller bubbles. The experimental results show that the proposed technique enables the generation of 2 ~ 70 µm diameter bubbles at frequency of 1 ~ 102 kHz.

MicroBubble manipulation using ultrasound field
We have been also working on bubble manipulation using ultrasound field. It is known that small bubbles having the natural frequency larger than the imposed ultrasound frequency tend to move toward the antinode of the standing wave. Using this phenomenon, bubble manipulation technique has been developed. Here, we show some results of break-up of microbubbles-encapsulated vesicle using ultrasound. First, the vesicles containing microbubbles were prepared and then the ultrasound field is imposed toward the vesicles. The vesicle membrane is broken effectively by the translational motion of bubbles due to the primary Bjerknes force, as shown in the movie.
Biographical Sketch: Shu Takagi is a Professor of fluid mechanics at Department of Mechanical Engineering, The University of Tokyo. After he obtained his doctor degree of engineering at the University of Tokyo in 1995, he became a research associate at the engineering school of the University of Tokyo. After that, he became a research associate of the Tokyo Institute of Technology, assistant and associate professor of The University of Tokyo, team leader in RIKEN, and the current professor position in 2010. He has been working on many topics related to fluid mechanics, especially in the field of dispersed multiphase flows, bio-mechanical flows, medical ultrasound, computational mechanics, and micro-nano scale flows. He was awarded JSME Young Engineer’s Award (1997), Japanese Society of Multiphase Flows, Best Paper Awards (1998), JSME Medals for Outstanding Paper (2007) etc. He is a fellow of Japan Society of Fluid Mechanics.