For the first time, researcher Peter Eshuis of the University of Twente in The Netherlands shows this phenomenon in granular matter using a high speed camera. His research gains a better understanding of the behaviour of these materials that are often used and produced in industry.
Convection can be noticed in water when it nears the boiling point. Rolling movements then occur, to get rid of excess heat: heated fluid rises and cooler water falls, causing a roll. A similar and beautiful effect is seen in little balls shaken hard: starting with an eruption of rising fast balls that go down again, clusters are formed and a rotating movement starts. Just like in fluid, there are balls with lower energy clustering and with higher energy, moving fast. Analogous to the temperature of the boiling plate heating fluids, the shaking energy gives rise to phase transitions.
Before convection starts, at lower shaking intensities, the balls already show behaviour typical to fluids: in fluids this is called the Leidenfrost effect, when a droplet is ‘floating’ on a thin layer of gas. The same happens with vertically shaken balls: a packed cluster of balls ‘floats’ on a layer of fast moving balls. This layer is therefore called ‘granular gas’. Eshuis describes the transition from the Leidenfrost condition towards convection. This is not just a matter of rising the level of energy, he found out: there has to be an instability that causes the onset of convection. This instability causes some balls to cluster and others to free themselves.
Granular matter like grain, sugar, sand and pills, often give rise to unexpected effects during transport, processing or storage. This often causes stagnation in industrial processes or excessive energy consumption. Better understanding of the behaviour of the materials, like Eshuis presents in his thesis, helps to prevent these effect. He also proves that many phenomena like clustering of grains can be explained by treating and describing the materials like fluids.
Peter Eshuis (1980) studied Applied Physics at the University of Twente and did his PhD-research within the Physics of Fluids research group of prof. Detlef Lohse, part of the Institute of Mechanics, Processes and Control (IMPACT) of the University of Twente.
Wiebe van der Veen | alfa
Tangled magnetic fields power cosmic particle accelerators
14.12.2018 | DOE/SLAC National Accelerator Laboratory
In search of missing worlds, Hubble finds a fast evaporating exoplanet
14.12.2018 | NASA/Goddard Space Flight Center
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
14.12.2018 | Power and Electrical Engineering
14.12.2018 | Physics and Astronomy
14.12.2018 | Physics and Astronomy