2019 Volume 36 Issue 4 Pages 291-
Correlation between ultrasonic behavior and solidification process of aqueous solution is studied with the aim to develop an ultrasonic technique for detecting various state quantities in the field of thermal-hydraulics with phase change. First, a simple ultrasonic measurement system was constructed, and then the solidification experiments were conducted by varying temperature and initial concentration of sodium chloride solution from 0 wt.% to almost eutectic composition, 23 wt.%. From the experiment, it was found that sound velocity was changed by ice crystal growth and/or salt-ice eutectic reaction. Next, the variation of sound velocity at each initial concentration was discussed in relation to the solidification process, on a temperature-sound velocity coordinate plane. Summarizing these results, we presented a novel three-dimensional acoustic phase diagram, in which information of sound velocity was added to temperature and composition as intensive variables. Thus sound velocities in each region of a liquid region, a mush region, and a solid region were characterized on the acoustic phase diagram. Finally, it was clarified that, based on the acoustic phase diagram, our noninvasive sound velocity measurement is able to detect various state quantities such as temperature, composition, and ice packing factor.
