A bad design can have serious consequences. In 2020, the Bloomberg agency revealed the misadventure of the US navy. Their new ships suffer from a defect that forces them to spend hundreds of thousands of dollars to unclog their toilets, which have the unfortunate tendency to clog too quickly.
This blocked pipe problem is not uncommon. In the human body, clots block arteries. In geophysics, wells are shut down because they become congested after fluid injection. To print walls or even entire buildings in cement or concrete, engineers hesitate about the diameters or flow rates to use so as not to clog the nozzles.
Other well-known examples of orifice-blocking particles exist in so-called “dry,” fluid-free environments, such as traffic jams, crowd evacuations, or the flow of grain in agricultural silos.
Even if these situations are banal, they remain largely misunderstood. It has even become a field of research, jamwhose activity has been growing rapidly for about fifteen years. In Physical Review Investigation On September 10, a team from the University of California, Santa Barbara added their two cents.
“random phenomenon”
There are three main ways to plug a hole in a flow whose diameter is reducing. This happens because the particles are larger than the hole (this is obvious, but, in non-homogeneous environments, it is not unusual to have particles of variable size). Or because the small particles add together, sticking together, forming larger ones that no longer pass.
Or, finally, they reach the funnel at the same time and block the flow, forming a shape identical to that of architectural vaults. The American team studied this last situation, the simplest. “This is still laborious, because the phenomenon is random and therefore requires carrying out up to fifty experiments to obtain a single relevant measurement point”underlines Alban Sauret, team director.
These researchers flowed distilled water containing polystyrene beads about half a millimeter in diameter through funnel-shaped channels at different angles. Viewed from a wide angle, they look like a syringe: liquid suddenly passes from a large reservoir into a small tube. At a small angle, on the other hand, the transition is smooth, as if there were only one tube. The configuration had already been studied for dry grains, with the conclusion that it is better to perform flows at small angles than at large ones.
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