Study on Fluid Control by Ultrasonic Wave

Introduction

In the future, it will be expected in micro gravity environment, such as a space shuttle and a space station, that development of new material is performed.
When manufacturing new material under minute gravity environment, in order that the buoyancy resulting from the difference of temperature in fluid or the density difference between different materials may not work, a convection does not take place and separation by precipitation is not generated, either.It is thought using such the characteristic that a large-sized single crystal and a homogeneous alloy which are not obtained on the earth can be manufactured.
Under micro gravity environment, since very small remains acceleration exists regularly, in order to process material, it is needed to make an object hold and drive by a certain power.
Then, in this research, acoustic standing wave of an ultrasonic wave was used, the system which holds and drives droplet was studied, and the characteristic was investigated.

Experimental conception

According to the ultrasonic wave emitted from upper and lower horns connected to the ultrasonic transducer, if acoustic standing wave is made to form in the space between horns, the distribution of sound pressure will arise. If droplet is poured into that space, it is expected that the droplet can be held in the specific place of standing wave. And it is expected that droplet can be driven when moving standing wave by changing the phase of the signal inputted into one of ultrasonic transducers.
Moreover, it is expected by investigating vibration of the surface of held droplet that the surface tension and the viscous coefficient of droplet can be measured.

Experimental set up

The schematic figure of experiment setup is shown in the right. A sign wave signal from a computer inputs into the ultrasonic transducer of each upper and lower sides through amplifier. This drives an ultrasonic transducer and acoustic standing wave is made to form in the space of a test section through the horns connected to the transducer. Moreover, we observed the action of droplet using the digital video camera, and change of the diameter of droplet is measured using a high precision digital measuring system.

Experimental result

The picture of the holding water droplet in this experiment is shown in the right. Droplet with a diameter of about 2mm is stably held to the space between up-and-down horns.The diameter of the largest droplet held in present experiment was about 8mm.
Moreover, about the drive of droplet, only about 1/10 drive distance of the value expected was acquired.

And physical properties measurement of water droplet was performed. Consequently, a difference with a known value is 0.81% about surface tension, and 23.6% about the viscous coefficient. The very good result were obtained.

A future subject (micro gravity experiment)

Now, the plan of the micro gravity experiment using the airplane which the Canada National Aeronautics and Space Administration (CSA) owns is advancing. Present micro gravity experiment is the same as the experiment conducted with NASA before. And the experiment with NASA having mainly been a thing about control of underwater air bubbles. In contrast, present experiment performs control of droplet and physical properties measurement which was described in this page.