Granular Bubbles

The flow of granular materials is a useful practice in industries such as pharmaceutical production and carbon capture. While granular particles are solid, the interaction of all the particles can act as a fluid and this behaviour can be exploited to improve efficiency in transporting and mixing these materials. “Fluidisation” requires an upward of flow of gas and vertical vibration enhances the effects of buoyancy in the fluids, which can lead to some quite interesting and even familiar behaviour.

Researchers at ETH Zürich and Columbia University have recently investigated binary granular fluids with a mix of light and heavy particles, and were able to observe classical fluid behaviour such as Rayleigh-Taylor instability. “Bubbles” of lighter particles were also observed to rise due to buoyancy and the fluid-like behaviour is very satisfying to watch. Other interesting features include separation of an initially mixed fluid and splitting of a heavy droplet in a sea of light particles.

The research caught my eye as the particle mixtures resemble some of our Molecular Dynamic simulation results of bubble flows, with fluids being composed of individual atoms. It would be very interesting to see if other bubble phenomena such as cavitation could also be reproduced with such binary granular flows.