On February 2, Associate Professor Tomohiro Inoue of the Graduate School of Engineering, the University of Tokyo, collaborated with Professor Yuichiro Iri and Professor Atsumi Miyake of Yokohama National University, and Professor Emmanuel Biermo of Aix-Marseille University to generate sparklers.・ Announced that it succeeded in high-speed photography with clear branches for the first time and revealed the main chemical reactions.In addition, the behavior of sparks was theoretically formulated.
Sparklers have been widely popular as one of the summer traditions since the Edo period.So far, it has been clarified that fireballs and sparks generate heat through a chemical reaction with ambient oxygen and are composed of potassium compounds, which are reaction products of black powder.On the other hand, it was difficult to take a clear picture of the sparks that went out and disappeared, and the sparks that color the sparklers were a mystery.
This time, the research group succeeded in shooting a clear time-series image of sparklers at 10 frames per second using the high-speed camera "Photron SA-Z".There are many bubbles on the surface of the fireball formed at the lower end of the twisted paper.These bubbles suddenly burst to create a flow driven by surface tension, and droplets with a diameter of 0.1 mm pop out at a speed of 1 m / s.This principle is the same as water droplets jumping from the bubbles of champagne poured into a glass, and the crackling sound of sparklers is also the sound of bursting bubbles.The afterimage of this popped out droplet looks like a spark.
As a result of this observation, it was found that the trajectory drawn by the droplets that jumped out of the fireball while dividing in a chain reaction up to eight times formed a pine needle spark.Normally, solids and liquids become stable after splitting once or twice, so they will not split any further unless external force is applied, whereas in sparklers, isolated droplets will be a child liquid for generations. Continue to make drops.In the paper, this new form of division is called successive fragmentation, and the series of self-similar phenomena created by it is called direct cascade.It became clear that the unique beauty of sparklers was created by the chain splitting of droplets, which is different from the previously known splitting phenomenon.
This research revealed one science that creates the beauty of sparklers, which has been popular since the Edo period.On the other hand, the mechanism by which sparks do not branch and become like willows has not yet been elucidated, and future research is expected.