Abstract
It is expected that pure and high performance materials could be manufactured in space under the micro-gravity environment.However, if bubbles are initially trapped in the molten material, they cannot escape from the material under the micro-gravity condition and could adversely affect the product quality.In the present study, an ultrasonic acoustic standing wave field is adopted to control the bubble motion under the micro-gravity environment.At first, a single ultrasonic transmitter was used to establish the acoustic standing wave field in a fluid with afree surface.It was experimentally confirmed under normal gravity that the bubble can be held stationary in the ultrasonic wave field.The experimental results were also confirmed by numerically solving the Rayleigh-Plesset equation and bubble motion equation in the translational direction.Next, the bubble control experiment was conducted by using dual ultrasonic vibrators.The ultrasonic acoustic standing wave field was moved by shifting the phase difference between the dual ultrasonic transmitters.It was experimentally confirmed that the bubble position can be controlled by moving the ultrasonic acoustic standing wave field.Finally, the bubble control technique by ultrasonic waves developed in ground experiments was verified for the reduced-gravity condition by conducting experiments aboard the KC-135 aircraft at NASA Johnson Space Center in the United States.It was experimentally confirmed that the present technique is applicable even under the reduced-gravity condition.It was also found that a larger bubble than that under normal gravity and a group of bubbles can be controlled under reduced-gravity by the present ultrasonic wave technique.
