Why is your stuff not separating: fluid flow inside centrifuges

The centrifuge, a common piece of equipment in most of our labs, has become also a useful tool in many kitchens in the last decade, specially in high-end restaurants. Centrifuges are used to separate samples based on the density of its components and there are a myriad of applications in which centrifuges can be used in a kitchen, e.g., extracting oil from a puree, or to thicken sauces by removing water.

On the one hand, it is desirable to separate the components as soon as possible, but on the other hand, a gentle separation is preferable to have well-separated layers. Clearly, the only motion wanted inside a centrifuge tube is a gentle separation of components. But observations inside a centrifuge tube while spinning are not trivial. Despite the difficulties, artist Maurice Mikkers installed a tiny camera inside a tuned-up centrifuge for his youtube's "The Centrifuge Camera Channel", where he films the separation of all kinds of stuff.

The footage from the centrifuge camera is surprising for any fluid dynamicists due to the amount of motion present in most videos, far from a gentle separation motion and persistent for minutes. In this presentation, I will show fluid flow measurements performed using Maurice's centrifuge to characterize such a flow. Combined with numerical simulations, we elucidated the role of the centrifugal and Coriolis forces in the system. Ultimately, we might be able to give a few tips how to prevent the outcome of such a flow within centrifuges, which can dramatically spoil your sauces and purees.