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

Zoom in / Can you determine the optimal angled urinal design to minimize splashing? It’s one second from the right.

Mia Shi/University of Waterloo

Scientists at the University of Waterloo have identified the optimal design for a splash-free urinal: a long, slender body of porcelain with curves reminiscent of a nautilus shell, dubbed “Nauti-loo”. This is good news for men who are tired of urine spilling on their pants and shoes – and for the poor souls who have to clean up every stain regularly. Bonus: It’s a very aesthetically pleasing design that gives the backbone of a public bathroom a touch of class.

“The idea originated exactly where you think it did,” Chow Pan of Waterloo told New Scientist. “I think most of us were a bit inattentive in our posts and looked down to find we were wearing spotted pants. No one likes to pee everywhere, so why not just make a urinal where splashing is highly unlikely?” offered graduate student Kaveeshan Thurairajah, The results of this research were presented 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 Tad Truscott, a mechanical engineer who founded the so-called “Splash Lab” at Utah State University. In 2013, the Splash Lab (then at Brigham Young University) provided some helpful advice on how men should avoid urine splashing their khaki pants while they hang out in the bathrooms. “Sitting on the toilet is the best approach, as there is less distance for the urine to cover on its journey to the bowl,” I previously wrote on Gizmodo. “If you choose the classic standing technique, scientists advise standing as close to the urinal as possible, and trying to direct the stream at an angle downward toward the back of the urinal.”

For those who lack optimal anti-splash technology, Randy Hurd, a Truscott graduate student, presented a perfect design for a splash-free urinal insert at the 2015 Fluid Dynamics meeting at APS. There are three basic types of entries. One uses an absorbent cloth to keep splashing to a minimum; another uses a honeycomb structure — a raised layer (held by small poles) with perforations — so that drops of urine pass through but no spray comes out; The third type contains a group of columns. However, absorbent fabrics cannot absorb liquid quickly enough and quickly become saturated, while structures consisting of hives and matrix columns do not prevent urine pools from gradually forming.

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

Hurd and Truscott’s interior design was inspired by a type of super-absorbent algae (Syntrichia caninervis) thrives in very dry climates and is therefore very good at collecting and storing as much water as possible. They found that the man-made substance called Fanta Black mimics algae’s absorbent properties. They copied the structure of this material for insertion into a urinal and found that it successfully stopped droplets of urine from escaping – effectively acting as a “urine black hole”.

Nor were the ladies excluded from this science pissing contest. Women also experience urine spillage, most notably when they need to urinate into a cup for medical testing purposes. In 2018, Splash Lab conducted a series of experiments involving a model of the anatomically correct female urethra. (They used a soft polymer to model the labia.) The findings inspired the (patented) design of the “Orchid,” a funnel-shaped attachment for urine cups that minimizes 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 academics working in this field.

According to Pan, the key to optimal design of a splash-free urinal is the angle at which the urine stream hits the porcelain surface; Get a small enough angle, and there won’t be any splashing. Instead, you get a smooth flow across the surface, which prevents drips from flying off. (And yes, there is a critical threshold at which the flow of urine shifts from splashing to flushing smoothly, because phase transitions are everywhere—even in our public restrooms.) And it turns out, dogs have already determined the optimal angle as they raise their legs to urinate, and when they pan et al. They designed this on a computer, and pegged the optimal angle for a human being at 30 degrees.

Marcel Duchamp
Zoom in / “La Fontaine” by Marcel Duchamp, photographed by Alfred Stieglitz in 291 art galleries after the 1917 Society of Independent Artists exhibition.

Pan and his team also conducted a series of experiments with dyed liquids sprayed in jets of varying speeds into a range of synthetic urinal designs (see top image) made of dense epoxy-coated foam – including a standard commercial shape and a urinal similar to the one used by Marcel Duchamp. in his famous (and controversial) 1917 art installation “La Fontaine”. They all produced varying degrees of stain, which the scientists wiped away with paper towels. They weighed the wet towels and compared that to how much the paper towels weighed when dried to determine the amount of spray. The heavier the wet towel, the larger the splattered stain.

The next step was to discover a design that would provide the optimal urine flow angle for men across a wide range of heights. Instead of the usual shallow box in the form of a rectangle, they landed on the curved structure of the nautilus shell. They repeated the simulated urine stream experiments with the prototypes, And there you are! They did not notice a single drop splattered. By comparison, other urinal designs produced up to 50 times more water than a sprinkler. There was one circular design with a triangle-shaped opening that performed better than Nauti-loo in trials, but Pan et al. Turn it down because it won’t work across a wide range of elevations.

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