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

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

Mia Shi/University of Waterloo

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

“The idea arose exactly where you think it did,” Zhao Pan of Waterloo told New Scientist. “I think most of us were a bit careless in our posts and looked down to find we had stained pants on. Nobody likes to pee everywhere so why not just make a urinal where the splash is highly unlikely?His graduate student Kavishan Thriyaraja is presenting the results of this research at last week’s American Physical Society (APS) meeting on fluid dynamics in Indianapolis.

This is not the first time scientists have tried to tackle this problem. Pan is a former graduate student of Tad Truscott, a mechanical engineer who runs the so-called “Splash lab” at Utah State University. In 2013, the Splash Lab (then at Brigham Young University) offered helpful advice on how men should avoid getting urine spray on their khakis while defecating on the toilet. “Sitting on the toilet is best because there is less distance the urine has to journey on the way to the bowl.” Previously written on Gizmodo. “If you choose the classic standing technique, the researchers recommend standing as close to the urinal as possible and trying to direct the flow diagonally down to the back of the urinal.”

For those who do not have an optimal anti-splash method, another Truscott graduate student, Randy Heard, offers Perfect Design For Splash-Free Urinal Insertion 2015 APS Fluid Dynamics Meeting. There are three basic types of input. An absorbent cloth is used to minimize splashes; another uses a honeycomb structure—a raised layer (held by small posts) with perforations—so that urine droplets pass through but no mist escapes; The third type contains a group of columns. However, absorbents cannot absorb liquid quickly enough and quickly become saturated, while structures consisting of beehives and matrix columns do not prevent the gradual formation of urine pools.

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

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

The ladies weren’t excluded from this scientific pissing contest either. Women also experience urine leakage, especially when they have to urinate into a cup for medical testing purposes. In 2018, Splash Lab conducted a series of experiments with a model of the anatomically correct female urethra. (They used a soft polymer to model the labia) Inspired by the results The (patented) design of “Orchid”, A funnel-shaped attachment For urine cups that reduces 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 stream of urine hits the porcelain surface; Get a small enough angle and there will be no splash. Instead, you get an even flow over the surface, which prevents droplets from flying off. (And yes, there is a critical threshold where the flow of urine goes smoothly from splash to flush, because phase transitions are everywhere—even in our public restrooms.) And it turns out that dogs have already determined the optimal angle when they lift their legs. to pee and when they pan et al. They designed this on a computer and set the optimal angle for a human to 30 degrees.

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 painted liquids sprayed in jets at different speeds into a variety of synthetic urinal designs (see top image) made of dense epoxy-coated foam—including a standard commercial mold and a urinal similar to one used by Marcel Duchamp in his famous (and controversial) art installation “La Fontaine” from 1917. They all produced varying degrees of spatter, which the researchers wiped off with paper towels. They weighed the wet towels and compared that to the amount of spray when the paper towels dried to estimate the amount of spray. The heavier the wet towels, the bigger the splash back.

The next step was to discover a design that would provide the optimal urine flow angle for men across a wide range of body sizes. Instead of the usual shallow box in the form of a rectangle, they settled on the curved structure of the nautilus shell. They repeated the simulated urine flow experiments with the prototypes, and voila! They did not notice a single drop that splashed. In comparison, other designs of urinals produced up to 50 times more water than a sprinkler. There was a circular design with a triangular opening that surpassed the Nauti-loo in trials, but the Pan et al. Turn it down as it doesn’t work at a wide range of heights.

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