Salar Azizi has been working on his PhD in Dresden since 2013. At the moment the young Iranian researcher is on parental leave – but even in his spare time he notices fluid dynamical processes all around him.

The heavy hoot turns many heads around. Only the ducks and swans, swimming at the shore of the river Elbe, don’t seem to be impressed by the noise the ship makes, while expelling a huge cloud of steam. Shortly afterwards it crosses the bridge Blue Wonder, which was built more than 100 years ago and is named after its pale blue coat of paint. On the other side of the river beautiful, antique mansions arise from the mountainous surface. The picturesque scenery seems to have a relaxing effect on the many people, who enjoy the sunny afternoon close to the water – except for one spectator.

“Everything is fluid dynamics,” Salar Azizi claims enthusiastically, while watching the ship passing by. This realization struck the PhD student from Iran, when he noticed, that these boats aren’t powered by a combustion motor, but by a steam engine and paddle wheels. “It’s basically a hydrodynamic process.” The young scientist knows what he is talking about. After all he studies similar incidents at the HZDR’s laboratories – however, not in horizontal streams, but in vertical ones: bubble columns. These apparatuses look almost like giant lava lamps. Instead of the slow-moving molten material it is filled, though, with gas and a liquid, in research scenarios often water.

1.000 images in a second

While cruising on the Elbe, many steamboats cross the bridge Blue Wonder. Source: Sächsische Dampfschiffahrt (DML BY)

Nevertheless, the sight of the fast-travelling bubbles, coalescing and breaking apart on their way to the top, seems to have the same calming effect – but again not on Salar Azizi. The situation resembles the moment at the shore of the Elbe. Whereas all the other people around him are merely impressed by the beauty, the chemical engineer observes not only the fascinating picture, but also the science behind it. “I try to develop models, which predict the size of the bubbles,” Salar Azizi describes his research. “Based on this knowledge we can optimize the design and, therefore, the efficiency of these reactors, which are widely used in the chemical industry.”

Since these flows are quite chaotic, Salar Azizi uses ultrafast X-ray tomography – a method, which was developed at the HZDR. By deploying a movable X-ray source, the stream can be radiographed at cross-sections of the opaque reactor. “1.000 images in just one second are an easy task for this technique,” Salar Azizi explains. “It, thus, becomes possible to follow single bubbles and their movement pattern through the columns.” Such possibilities were one of the reasons which drew the Iranian researcher to Germany. Compared to his subject of study Azizi’s situation in the Saxon capital is almost the opposite, though. “Life in Dresden is much more stable than in my home town Urmia. This in turn makes me more relaxed as well.”

The scientist noticed this especially, when his son was born in Germany, while he was away on a research stay in India: “He came earlier than expected. But I was not really worried, because I knew my family was in good hands at the university hospital in Dresden. And when I returned my son already waited for me and everything was great.” Now Salar Azizi is looking forward to see him growing up in Germany – the scenery at Blue Wonder will probably soon have one more fascinated spectator.