The first ever camera footage from inside a centrifuge has revealed a new mystery in the physics of fluids.
A centrifuge is a standard piece of laboratory equipment that spins fluid samples at high speed to separate out their components. For instance, centrifuging a blood sample will separate the red blood cells from the white ones. This is because spinning produces the centrifugal force, the same force that pushes clothes towards the edges of a spinning washing machine drum. This acts on the components of the fluid to a differing degree depending on their densities, and so pulls those different components apart from one another.
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鈥淲hen I was working in a lab, I used the centrifuge many times a day,鈥� says , an artist based in the Netherlands. Because the centrifuge is an enclosed piece of equipment, Mikkers couldn鈥檛 view the separation process as it unfolded in real time. But he began to wonder what that process actually looks like. 鈥淚 wrote the idea down in my notebook and left it there for years until I started to do visual arts. Then I started building a camera into the centrifuge.鈥�
The work wasn鈥檛 easy: accelerations inside centrifuges are very strong 鈥� as much as 2500 times the strength of Earth鈥檚 gravity 鈥� which can make cameras and electronics fall apart. 鈥淚 did blow up a lot of cameras at first,鈥� says Mikkers.
He contacted , who researchers the physics of fluids at the University of Twente, also in the Netherlands, to work on the project. When Mikkers, Marin and their colleagues looked at the first footage from inside the camera-equipped centrifuge, Marin says that they didn鈥檛 understand anything they saw.
Textbooks typically state that fluid components separate slowly and smoothly during centrifuging, Marin says, but that isn鈥檛 what the camera recorded.
For instance, when spinning shower gel 鈥� a liquid full of suspended reflective particles 鈥� the researchers saw swirling patterns, 鈥渧ery violent little tornadoes鈥�, instead of a smooth liquid, says at the Delft University of Technology in the Netherlands who worked on the project. When they swapped shower gel for dirty water like that processed in waste-water treatment plants, they still observed the swirling effect 鈥� it wasn鈥檛 just a shower gel quirk.
鈥淲e don鈥檛 understand even the simple fluids, very basic ones like water with some particles inside,鈥� says Botto.
Simulating aspects of the centrifuging process on a computer helped eliminate some hypotheses about what caused the vortices 鈥� for instance, that they could be explained by changes in the fluid鈥檚 temperature. But the researchers are still investigating their origin. Currently, based on targeted laboratory experiments and computer simulations, they think that a slight shaking of the centrifuge may be the culprit.
Marin presented the research at the in Washington DC on 19 November.
While Mikkers鈥檚 in-centrifuge camera uncovered an overlooked effect in the physics of fluids, the finding could also have implications in the food processing and pharmaceutical industries where centrifuges are used to purify products. Vortices mix the fluid components that would otherwise be separated within a centrifuge, so understanding what causes them to form might be important for finding ways to eliminate them and make centrifuges work more efficiently, says Marin.
