What is the best design for a splash-free urinal? Physics now has the answer

What is the best design for a splash-free urinal? Physics now has the answer

Do you see the urinal design with the optimal splash-reducing angle?  It's that one second from the right.
Enlarge / Do you see the urinal design with the optimal splash-reducing angle? It’s that one second from the right.

Mia Shi/University of Waterloo

Scientists at the University of Waterloo have determined the optimal design for a splash-free urinal: a long, slender porcelain structure with curves reminiscent of a nautilus shell, playfully dubbed the “Nauti-loo”. That’s good news for men tired of having urine splattered on their pants and shoes – and for the poor souls who regularly have to clean up all the splatter. Bonus: It’s quite an aesthetically pleasing design, giving this workhorse of the public restroom a touch of class.

“The idea originated exactly where you think it originated,” says Waterloo’s Zhao Pan told New Scientist. “I think most of us have been a little inattentive to our post and looked down to see we were wearing speckled pants. Nobody likes to pee everywhere, so why not just make a urinal where splashing is extremely unlikely?” His graduate student, Kaveeshan Thurairajah, presented the results of this study at last week’s American Physical Society (APS). meeting on fluid dynamics in Indianapolis.

It’s not the first time scientists have tried to tackle this problem. Pan is a former graduate student of Tadd Truscott, a mechanical engineer who is known as the “Splash labat Utah State University. In 2013, the Splash Lab (then at Brigham Young University) offered some helpful tips on how men could avoid getting their khaki pants stained with urine splashes while defecating in restrooms. sitting is the best technique, as there is less distance for the puddle to travel on its journey to the bowl,” I previously wrote on Gizmodo. “If you opt for the classic standing technique, the scientists recommended standing as close to the urinal as possible and trying to direct the flow at a downward angle to the back of the urinal.”

For those who don’t have optimal anti-splash technique, another of Truscott’s graduate students, Randy Hurd, presented an optimal design for a splash-free urinal insert the 2015 APS fluid dynamics meeting. There are three basic types of inserts. Absorbent cloth is used to minimize splashing; another uses a honeycomb structure – a raised layer (held up by small pillars) with holes – so that urine drops pass through but no splashes come out; and a third type with a series of pillars. However, absorbents cannot absorb liquid fast enough and become saturated quickly, while the honeycomb structure and the layered pillar structures do not prevent the gradual formation of urine pools.

In 2013, the Splash Lab showed that less urine splashing can be achieved by aiming at a vertical surface, moving closer to the urinal, and reducing the impact angle.

Hurd and Truscott’s insert design was inspired by a type of super-absorbent moss (Syntrichia canine fish) which thrives in very dry climates and thus is very good at collecting and storing as much water as possible. And they found that the man-made material “VantaBlackmimicked the absorbent properties of the moss. They copied that material’s structure for their urinal insert and found that it successfully blocked pee droplets from escaping – effectively acting as a “urinal black hole.”

Nor have the ladies been left out of this scientific (ahem) piss contest. Women also suffer from urine leakage, especially when they have to urinate in a cup for medical testing purposes. In 2018, the Splash Lab conducted a series of experiments using a model of an anatomically correct female urethra. (They used a soft polymer to model the labia.) The result inspired the (patented) design of the “Orchid”, a funnel-shaped attachment for urine cups that reduce spillage. The research could lead to devices that allow women to urinate standing up, which would be a boon for women in the military or female academics working in the field.

According to Pan, the key to optimal splash-free urinal design is the angle at which the urination jet hits the porcelain surface; get a small enough angle, and there won’t be a spatter. Instead, you get a smooth stream across the surface, preventing droplets from flying out. (And yes, there’s a critical threshold at which the urine stream switches from splashing to smooth flowing, because phase transitions are everywhere — even in our public restrooms.) As it turns out, dogs have already determined the optimal angle when they bend their legs to urinate, and when Pan et al. modeled on a computer, they determined the optimal angle for humans at 30 degrees.

Marcel Duchamps "Fountain," photographed by Alfred Stieglitz at art gallery 291 after the 1917 Society of Independent Artists exhibition.
Enlarge / “La Fontaine” by Marcel Duchamp, photographed by Alfred Stieglitz at art gallery 291 after the 1917 Society of Independent Artists exhibition.

Pan and his team also conducted a series of experiments with painted liquids sprayed in jets at different velocities into a series of mock urinal designs (see top photo) made of dense, epoxy-covered foam, including the standard commercial form and a similar urinal . after the one used by Marcel Duchamp in his famous (and controversial) 1917 art installation”FountainThey all produced varying degrees of splash water, which the scientists wiped up with paper towels. They weighed the wet towels and compared that to how much the paper towels weighed when dry to quantify the amount of splashing. The more the wet towels weighed, the bigger the back wall.

The next step was to come up with a design that would provide that optimal urinary flow angle for men across a wide range of body sizes. Instead of the usual shallow box in the shape of a rectangle, they ended up on the curved structure of the nautilus shell. They repeated the simulated urine flow experiments with the prototypes, and there you go! They did not see a single drop splash back. In comparison, the other urinal designs produced as much as 50 times more splash water. There was one round design with a triangular opening that outperformed the Nauti-loo in the experiments, but Pan et al. rejected it because it wouldn’t work at a wide range of heights.

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