What’s the best design for splash-free urinal? Physics now has the answer

The best design for a splash-free urinal is a tall, slender porcelain structure with curves reminiscent of a nautilus shell, according to scientists at the University of Waterloo. It's good news for men who don't want their urine on their pants and shoes, and it's bad news for the poor who have to clean up all the urine. This workhorse of the public restroom design is quite attractive and gives it a touch of class.

Waterloo's Zhao Pan told New Scientist that the idea came from there. Most of us have been a little careless at our post and looked down to see we were wearing speckled pants. Wouldn't it be great to create a urinal where pee isn't splattered? The results of this research were presented by his graduate student at theAPS meeting.

Scientists have addressed this issue before. A mechanical engineer named Tadd Truscott founded the " Splash Lab" at Utah State University. The Splash Lab at Brigham Young University offered a few tips on how to avoid peeing in a restroom while wearing khakis. "Sitting on the toilet is the best way to pee since there is less distance for the pee to cover on its journey to the bowl," I wrote at Gizmodo. The scientists advised standing as close to the urinal as possible, and trying to direct the stream at a downward angle towards the back of the urinal.

At the 2015APS fluid dynamics meeting, a graduate student from Truscott presented an optimal design for a splash-free urinal insert. Three types of inserts are available. One uses absorbent cloth to keep splashing, another uses a honeycomb structure with holes, and a third uses pillars. The honeycomb and arrayed pillar structures don't prevent urine pools from forming because absorbent fabrics can't absorb liquid quickly enough.

A type of super-absorbent moss that thrives in very dry climates is what inspired the insert design. The moss' absorbent properties were mimicked by the Vanta Black material. They found that the material they used for their urinal insert acted as a urinal black hole, blocking droplets of pee from escaping.

The ladies have been included in the contest. When women need to pee into a cup for medical testing, they also suffer from urine spillage. A model of a female urethra was used in a series of experiments. The labia was modeled using a soft plastic. The design of the "Orchid" was inspired by the results. The research could lead to devices that allow women to pee standing up, which would be great for women in the military or female academics.

Pan says that the key to a splash-free urinal design is the angle at which the pee stream strikes the porcelain surface. You get a smooth flow across the surface. There is a critical threshold at which the urine stream can switch from splashing to flowing smoothly. The optimal angle for humans was pegged at 30 degrees by Pan et al., after they modeled this on a computer.

Pan and his team also conducted a series of experiments with dyed fluids sprayed in jets of differing speeds into a range of faux-urinal designs made of dense, epoxy-covered foam. The scientists wiped up the splash back with paper towels. They weighed the wet towels to see how much they weighed when dry. The bigger the towel, the bigger the splashback.

The next step was to figure out a design that would allow men across a wide range of heights to urinate. They landed on the curved structure of the naUtilus shell instead of the usual shallow box. The simulations were repeated with the prototypes. They didn't see any droplets splashing. The urinal designs produced more splashback than the other ones. Pan and his team rejected the round design because it wouldn't work across a wide range of heights.