Upstream contamination by floating particles is a counterintuitive phenomenon in

fluid dynamics In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids— liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) an ...

. When pouring water from a higher container to a lower one, particles floating in the latter can climb upstream into the upper container. A definitive explanation is still lacking: experimental and computational evidence indicates that the contamination is chiefly driven by

surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to f ...

gradients, however the phenomenon is also affected by the dynamics of swirling flows that remain to be fully investigated.

Origins

Experimental setup for upstream contamination

The phenomenon was observed in 2008 by the Argentine Sebastian Bianchini during

mate Mate may refer to: Science * Mate, one of a pair of animals involved in: ** Mate choice, intersexual selection ** Mating * Multi-antimicrobial extrusion protein, or MATE, an efflux transporter family of proteins Person or title * Friendship ...

tea preparation, while studying physics at the

University of Havana The University of Havana or (UH, ''Universidad de La Habana'') is a university located in the Vedado district of Havana, the capital of the Republic of Cuba. Founded on January 5, 1728, the university is the oldest in Cuba, and one of the first ...

. It rapidly attracted the interest of professor Alejandro Lage-Castellanos, who performed, with Bianchini, a series of controlled experiments. Later on professor Ernesto Altshuler completed the trio in

Havana Havana (; Spanish: ''La Habana'' ) is the capital and largest city of Cuba. The heart of the La Habana Province, Havana is the country's main port and commercial center.

, which resulted in the Diploma thesis of Bianchini and a short original paper posted in the web arXiv and mentioned as a surprising fact in some online journals. Bianchini's Diploma thesis showed that the phenomenon could be reproduced in a controlled laboratory setting using mate leaves or chalk powder as contaminants, and that temperature gradients (hot in the top, cold in the bottom) were not necessary to generate the effect. The research also showed that surface tension was a key element to the explanation through the so-called

Marangoni effect The Marangoni effect (also called the Gibbs–Marangoni effect) is the mass transfer along an interface between two phases due to a gradient of the surface tension. In the case of temperature dependence, this phenomenon may be called thermo-capill ...

, which was suggested by two facts: (a) both mate and chalk lowered the surface tension of water, and (b) if an industrial surfactant was added on the upper reservoir, the upstream motion of particles would stop.

Confirmation

After a talk by Lage-Castellanos at the First Workshop on Complex Matter Physics in Havana (MarchCOMeeting'2012), professor Troy Shinbrot of

Rutgers University Rutgers University (; RU), officially Rutgers, The State University of New Jersey, is a Public university, public land-grant research university consisting of four campuses in New Jersey. Chartered in 1766, Rutgers was originally called Queen's ...

became interested in the subject. Together with student Theo Siu, Cuban results were confirmed and expanded with new experiments and numerical simulations at Rutgers, which resulted in a joint peer-reviewed paper. Later on, the phenomenon was confirmed independently by others. Whether dynamical behaviors of the falling water play a role remains as an open question. Videos of the effect are available on YouTube.

Implications

The phenomenon of upstream contamination could be relevant to industrial and biotechnological processes, and may be connected even to movements of the

protoplasm Protoplasm (; ) is the living part of a cell that is surrounded by a plasma membrane. It is a mixture of small molecules such as ions, monosaccharides, amino acid, and macromolecules such as proteins, polysaccharides, lipids, etc. In some defini ...

. It could imply that some of the

good practice GxP is a general abbreviation for the "good practice" quality guidelines and regulations. The "x" stands for the various fields, including the pharmaceutical and food industries, for example good agricultural practice, or GAP. A "c" or "C" is ...

s in industrial and biotechnological procedures need revision.

References

{{Reflist Fluid dynamics Physical paradoxes Physical phenomena

Origins

Confirmation

Implications

See also

References