Thick Fluids like Honey Flow Faster Than Water in These Tubes

Physicists in Finland discovered a coating that makes thick fluids flow 10 times more quickly than water in tubes.
Fabienne Lang
Honey dropletsAalto University

Honey can flow faster than water. Ten times faster, in fact. 

There's a little caveat though, as the honey—or any other viscous fluid–needs to be in a specifically-coated tube or encasing to do so. 

Scientists from the University of Aalto, in Finland, made the interesting discovery that fluids that were a thousand times more viscous than water could flow that quickly when capillaries, or tubes, were specially coated. 

Their findings were published in the journal Science Advances on October 16th.


Speed and coating

The new discovery could prove extremely useful in a number of applications, from industrial processes such as oil refineries to the medical sphere eg. the human heart. 

Typically, in order to make a liquid pump through a pipe, pressure needs to be applied. This, however, can prove tricky at times as the pressure needs to be just right in order not to burst the pipe. 

Hence why researchers have been looking into other methods of moving liquids of all kinds through pipes. 

Thick Fluids like Honey Flow Faster Than Water in These Tubes
Honey in one of the coated tubes. Source: Aalto University

The team of researchers from Aalto University found that by coating the inside of pipes with specific compounds that repel liquids, they ended up moving through them much more rapidly. 

The answer lies in the air. "A superhydrophobic surface consists of tiny bumps that trap air within the coating so that a liquid droplet that rests on the surface sits as if on a cushion of air," explained Professor Robin Ras from Aalto University. 

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The superhydrophobic coating needs to be in a tube, otherwise, it won't work properly. Inside a tube, the coating works to create a small air gap between the inside wall of the tube and the outside of the droplet. 

"This larger air gap is what allowed for the viscous fluids to move through the tube faster than the less viscous ones when flowing due to gravity," explained Dr. Maja Vuckovac, first author of the paper. 

The team has created a fluid dynamics model that can be applied to predict how droplets from different fluids would move within tubes coated with different superhydrophobic coatings.

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