14. Other aspects of Transport Phenomena

This study aimed to develop a novel reactor in which a droplet on a flat plate is actively vibrated using a low-frequency vibration device. Visualization experiments using UV-excited fluorescent particles with sufficiently small Stokes number revealed that the time when two stable circulating flows were formed inside the droplet occupied more than 70% of the measurement time. In addition to the two circulation patterns observed in most cases, 3 ~ 4 circulation patterns and unstable circulation patterns with time variations were also observed. The appearance of these circulating flow patterns were found to be independent of the oscillation frequency. The iodine-sodium thiosulfate decolorization reaction was also used to observe the mixing behavior in a droplet. It was found that the larger the amplitude and the lower the frequency, the higher the mixing efficiency. This may be due to the contribution of the circulating flow to the mixing performance in the droplet and the change in the internal flow depending on the vibration conditions. Numerical results obtained from Moving Particle Semi-implicit (MPS) method indicated that the internal flow of the droplet is a random flow field in the horizontal cross section. These internal flows were confirmed to be formed in all conditions regardless of the vibration conditions. It was also found that the flow near the droplet surface had higher turbulent intensity more turbulent as the amplitude increased. On the other hand, the results of the vorticity analysis of the vertical cross section of the droplet confirmed the existence of two circulating flows in the droplet. Evaluation using information entropy and mixing degree revealed that fluid particles tend to jump out of the circulating flow when the amplitude is increased, and this deviation of particle from the circulating flow orbit is a factor that promotes mixing.