Brussels, 07 Jan 2004
Using a high speed video camera, a team of Belgian scientists has, for the first time, succeeded in observing how 'antibubbles' form and move.
Whereas the common bubble is a spherical film of liquid that surrounds a pocket of air, an antibubble is a spherical shell of air containing liquid, and surrounded by liquid. Antibubbles also move downwards, while normal bubbles rise to the surface.
'Antibubbles are mysterious phenomena, but we now understand them much better,' said Stéphane Dorbolo, who led the research. 'We have come up with a good model describing how they form and move, and have also learnt more about the type of liquids that you can create them in,' he added.
To create their antibubbles, Dr Dorbolo and colleagues slowly poured a small amount of a soap and water solution over the surface of a glass tray containing the same liquid. They were able to watch as a jet of liquid globules formed beneath the surface, then broke up to form a stream of antibubbles that lasted for up to two minutes. The antibubbles then collapsed. The team believes that both the formation and collapse of the antibubbles are due to fluid instabilities.
To their surprise, the researchers also succeeded in creating antibubbles in beer. 'We tried to create them in beer for fun, and didn't think it would be possible, but were amazed when we managed to create giant antibubbles which lasted for almost two minutes [...]. You can't create antibubbles in pure water, alcohol or oil. But beer is a special case because it is very similar to dishwashing liquid and contains what we call surfactants, which is what you need to be able to produce antibubbles.'
But why are antibubbles important? Understanding the phenomenon could lead to a better understanding of the physics of fluids, and is of particular importance for engineers.
When water is cooled at nuclear reactors and following other large scale exothermic chemical processes, the number of bubbles present in the water is monitored in order to assess to what extent cooling capacity has been degraded by their presence. Process control parameters and cooling water flow are modified to compensate for this, but if the bubbles detected are actually antibubbles, the degree of adjustment needed will have been overestimated. This could have adverse effects on the process control system, and in extreme cases, could lead to damage to the plant and its surroundings.