Tokyo | Using Japan’s most powerful computer, researchers have explored how the physics of champagne bubbles may enable the design of more efficient power stations or propellers. Uncork a bottle of champagne, and as the pressure of the liquid is abruptly removed, bubbles immediately form and then rapidly begin the process of coarsening, in which larger bubbles grow at the expense of smaller ones, researchers said.
This fundamental nonequilibrium phenomenon is known as Ostwald ripening, and though it is most familiar for its role in bubbly beverages, it is also seen in a wide range of scientific systems including spin systems, foams and metallic alloys. Researchers from the University of Tokyo, Kyusyu University and RIKEN in Japan were able to simulate bubble nucleation from the molecular level by harnessing the K computer at RIKEN, the most powerful system in Japan.
At the heart of their work were molecular dynamics simulations. The basic concept behind these simulations is to put some virtual molecules in a box, assign them initial velocities and study how they continue moving – by using Newton’s law of motion to determine their position over time. A huge number of molecules, however, are necessary to simulate bubbles – on the order of 10,000 are required to express a bubble, said Hiroshi Watanabe, a research associate at the University of Tokyo’s Institute for Solid State Physics. So we needed at least this many to investigate hundreds of millions of molecules – a feat not possible on a single computer, said Watanabe.
The team wound up simulating a whopping 700 million particles, following their collective motions through a million time steps – a feat they accomplished by performing massively parallel simulations using 4,000 processors on the K computer. This was, to the best of their knowledge, the first simulation to investigate multi-bubble nuclei without relying on any artificial conditions. An enhanced understanding of the behaviour of bubbles is very important for the field of engineering because it may enable the design of more efficient power stations or propellers, researchers said. The study was published in The Journal of Chemical Physics.