What is the best design for a splashless urinal? Physics now has the answer

What is the best design for a splashless urinal? Physics now has the answer

Increase / Can you spot the urinal design with the optimal angle to reduce splashing? That’s 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 tall, slender porcelain structure with curves reminiscent of a nautilus shell, playfully named “Nauti-loo.” That’s good news for men tired of splashing urine on their pants and shoes—and for the poor souls who have to regularly clean up all the splashes. Bonus: It’s a pretty aesthetically pleasing design, giving this public restroom workhorse a touch of class.

“The idea was born just where you think it was born,” Zhao Pan of Waterloo he told New Scientist. “I think most of us were a little careless about our post and looked down and discovered we were wearing colorful 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 research during last week’s American Physical Society (APS) meeting on fluid dynamics in Indianapolis.

This is not the first time that scientists have tried to tackle this problem. Pan is a former graduate student of Tadd Truscott, a mechanical engineer who founded the so-calledSplash Lab” at Utah State University. In 2013, the Splash Lab (then at Brigham Young University) offered some handy tips on how men can avoid peeing their khaki pants while relieving themselves in restrooms. “Sitting on the toilet is the best technique because there is less distance that urine has to travel on its way to the container,” I wrote earlier in Gizmodo. “If you opt for the classic standing technique, scientists advise standing as close to the urinal as possible and trying to direct the stream at a downward angle towards the back of the urinal.”

For those lacking optimal anti-splash technique, another of Truscott’s graduate students, Randy Hurd, presented optimal design for a splash-free urinal insert on in 2015 APS Meeting on Fluid Dynamics. There are three basic types of inserts. An absorbent cloth is used to minimize splashes; another uses a honeycomb structure – a raised layer (held up by small posts) with holes – so that droplets of urine pass through but the splash does not escape; and the third type with a series of columns. However, absorbent fabrics cannot absorb liquid quickly enough and soon become saturated, while the honeycomb and pillar structures do not prevent pools of urine from gradually forming.

In 2013, Splash Lab showed that reducing urine splash can be achieved by targeting a vertical surface, moving closer to the urinal and reducing the angle of impact.

Hurd and Truscott’s insert design drew inspiration from a type of super-absorbent moss (Syntrichia caninervis) that thrives in very dry climates and is therefore very good at collecting and storing as much water as possible. And they discovered that an artificial material called “VantaBlack” mimic the absorbent properties of moss. They copied the material’s structure for their urinal liner and found it successfully blocked urine droplets from escaping – effectively acting as a “urinal black hole”.

The ladies aren’t left out of this scientific (ahh) pissing contest either. Women, too, suffer from urine spillage, especially when they need to pee in a cup for medical testing. In 2018, Splash Lab conducted a series of experiments involving a model of an anatomically correct female urethra. (They used a soft polymer to model the labia.) inspired results (patented) “Orchid” design, a funnel-shaped extension for urine cups that reduce spillage. The research could lead to devices that allow women to pee standing up, a boon for women in the military or for female academics working in the field.

According to Pan, the key to optimal splash-free urinal design is the angle at which the stream of urine hits the porcelain surface; get a small enough angle and there will be no kickback. Instead, you get a smooth flow over the surface, preventing droplets from flying out. (And yes, there is a critical threshold at which the stream of urine goes from splashing to smooth flow, because phase transitions are everywhere — even in our public toilets.) It turns out that dogs have already figured out the optimal angle when they lift their legs to pee, and when Pan et al. they modeled this on a computer, they determined the optimal angle for humans to be 30 degrees.

Marcel Duchamp "fountain," photographed by Alfred Stieglitz at Art Gallery 291 after the Society of Independent Artists exhibition in 1917.
Increase / “La Fontaine” by Marcel Duchamp, photographed by Alfred Stieglitz at Art Gallery 291 after the Society of Independent Artists exhibition in 1917.

Pan and his team also conducted a series of experiments with colored liquids sprayed in jets of varying speeds into a series of fake urinal designs (see photo above) made of thick foam covered in epoxy – including a standard commercial shape and a similar urinal to the one Marcel Duchamp used in his to the famous (and controversial) art installation from 1917.Fountain.” They all produced varying degrees of spray, which the scientists wiped up with paper towels. They weighed the wet towels and compared that to how much the paper towels weighed when they were dry to quantify the amount of spray. The heavier the wet towels, the greater the recoil .

The next step was to find a design that would offer the optimal angle of urine flow for men of a wide range of heights. Instead of the usual shallow rectangular box, they landed on the curved structure of a nautilus shell. They repeated the simulated urine stream experiments with prototypes, and here it is! They didn’t notice a single drop that splashed back. By comparison, other urinal designs produced as much as 50 times more backlash. There was one round design with a triangular opening that outperformed the Nauti-loo in experiments, but Pan et al. rejected because it wouldn’t work in a wide range of heights.

#design #splashless #urinal #Physics #answer

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