Your sewers have T-junctions -- places were two pipes come together and form a "T" shape. So do your arteries. A new study has found that these junctions can trap tiny particles of matter, blocking normal healthy flow.
Here's a video of the supposedly busy intersection of two streams of fluid. Liquid is rushing around in multiple directions. So why is a stable line of particles forming, like a group of well-behaved fifth graders waiting to get into the classroom?
It seems that t-junctions just form traps, where particles get stuck. According to a study on the subject, "material dispersed in the continuous phase fluid interacts with a vortical flow that develops at the T junction. As a result suspended particles can enter the vortices and, for a wide range of common flow conditions, the particles do not leave the bifurcation."
Low-density particles, like air bubbles, are especially prone to getting trapped. This is bad news if you want to clear your pipes, and especially bad news if you want clear blood vessels. It's good news for those who want an easy way to separate low-density particles from a liquid. No grills or gratings, just design the right T-junction and the particles will separate themselves out. And, of course, it's fun to watch.