Development of an Ultrasonic Tomography
Purpose
In two-phase flow, void fraction is one of the important parameters. It is well known that the void fraction distribution changes with the bubble diameter in bubbly flow.
And the liquid turbulence and the bubbles motion are related each other. Many techniques have been developed for measuring void distributions.
However, it is so limited for measuring the void fraction distribution in opaque fluid such as liquid-metal two-phase flow.
Ultrasonic tomography is a powerful tool for measuring void distribution in opaque fluid. However, the temporal resolution for measuring a cross-sectional information is limited because of the speed of sound.
Purpose of this study is developing a fast ultrasonic tomography for measuring instantaneous void distribution at a sampling rate of 1,000.
Research content
 Fig. 1 Time-series of the void distribution |
In order to improve the time resolution, it is required to reduce the number of sensor. In this study, a wide-angle ultrasonic transducer has been employed for fan shaped ultrasonic beam.
A tomography system based on the reflection method was developed using the 8 sensors. Ultrasonic is emitted at the sensors in turn, and the signals are received at the all sensors.
Two-dimensional void distribution can be obtained based on the echo intensity.
The developed system has been tested for bubble column with inner diameter of 50 mm. Bubbles are injected through needles at bottom of the container.
Pulse emission interval was set at 0.125 ms resulting in the time-resolution of 1 ms. The measurements were continuously carried out with 500 frames per second.
Pseudo-3D void distributions are obtained using the consecutive reconstructed images as shown in Fig. 1. Fig. 2 shows that the time-series of void distribution in water/argon case synchronizing with the flow visualization.
It is shown that the three-dimensional void distributions are clearly observed. This technique has been applied for measuring liquid-metal two-phase flows.
Publications
H. Murakawa, T. Shimizu, S. Eckert
Development of a high-speed ultrasonic tomography system for measurements of rising bubbles in a horizontal cross-section, Measurement 182, 109654 (2021). https://doi.org/10.1016/j.measurement.2021.109654
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